java theroy ! easy to learn

7/31/2019 Java Theroy ! Easy to Learn

1/53

Q. Why is Java often termed as a platform?A n s : P l a t f o r m i s t h e e n v i r o n m e n t i n w h i c h p r o g r a m s

e x e c u t e . I n s t e a d o f i n t e r a c t i n g w i t h t h e

O p e r a t i n g S y s t e m d i r e c t l y , J a v a p r o g r a m s r u n s o n a

v i r t u a l m a c h i n e p r o v i d e d b y J a v a , t h e r e f o r e J a v a i s

o f t e n r e f e r r e d t o a s a p l a t f o r m a l s o .Q. What is a bytecode?A n s : B y t e c o d e i s a s e t o f p s e u d o m e c h a n i c

l a n g u a g e i n s t r u c t i o n s t h a t a r e u n d e r s t o o d b y t h e

J V M ( J a v a V i r t u a l M a c h i n e ) a n d a r e i n d e p e n d e n t

o f t h e u n d e r l y i n g h a r d w a r e .

Q. What do you understand by JVM?

A n s : J V M o r J a v a V i r t u a l M a c h i n e i s a n a b s t r a c tm a c h i n e d e s i g n e d t o b e i m p l e m e n t e d o n t o p o f

e x i s t i n g p r o c e s s o r s . I t h i d e s t h e u n d e r l y i n g O S f r o m

J a v a a p p l i c a t i o n . P r o g r a m s w r i t t e n i n J a v a a r ec o m p i l e d i n t o J a v a b y t e - c o d e , w h i c h i s t h e n

i n t e r p r e t e d b y a s p e c i a l j a v a I n t e r p r e t e r f o r as p e c i f i c p l a t f o r m . A c t u a l l y t h i s J a v a i n t e r p r e t e r i s

k n o w n a s J a v a V i r t u a l M a c h i n e ( J V M ) .

Q. What is JDK (Java Development Kit)?A n s : T h e J a v a d e v e l o p m e n t k i t c o m e s w i t h a

c o l l e c t i o n o f t o o l s t h a t a r e u s e d f o r d e v e l o p i n g

a n d r u n n i n g j a v a p r o g r a m s .Q. What are Java APIs?

A n s : T h e J a v a A P I s ( A p p l i c a t i o n P r o g r a m I n t e r f a c e )

c o n s i s t o f l i b r a r i e s o f p r e - c o m p i l e d c o d et h a t p r o g r a m m e r s c a n u s e i n t h e i r a p p l i c a t i o n .

Q. Write the five characteristics of Java/BlueJ?

Top Companies Hiring. If Your CV Is Ready, Register Now With Shine.com!

www.Shine.Com/Teaching_Jobs

Companies Hiring Freshers Now. Sign up for Free to Apply.

MonsterIndia.com

10,000+ Job Openings across India Upload Resume.Apply to TATA Now!TimesJobs.com/TATA-Hiring

I C S E B l u e JT h e o r y h t t p : / / w w w . a m

i t a b h s i r k i c l a s s e s . o

r g . i n / m a t e r i a l s / i c s

e / j t h e o r y . h t m 1


2/53

o f2 4 8

/ 2 0

/ 2 0

1 1

1 1 :2 7P M

A n s : 1 . W r i t e O n c e R u n A n y w h e r e 2 . L i g h t w e i g h t

c o d e 3 . S e c u r i t y 4 . B u i l t i n G r a p h i c s 5 . O b j e c t

O r i e n t e d L a n g u a g e 6 . S u p p o r t M u l t i m e d i a 7 . P l a t f o r m

I n d e p e n d e n t . 8 . O p e n P r o d u c t .

Q. What do you know about BlueJ?A n s : B l u e J i s a J a v a d e v e l o p m e n t e n v i r o n m e n t . I t i s

a n I D E ( I n t e g r a t e d D e v e l o p m e n t E n v i r o n m e n t ) ,

w h i c h i n c l u d e s a n e d i t o r a d e b u g g e r a n d av i e w e r .

Q. How you create, compile and execute a program in Java or BlueJ? Explain youranswer?

A n s : C r e a t e : C l i c k o n n e w c l a s s b u t t o n f r o m B l u e J

e d i t o r , t h e n t y p e t h e c l a s s n a m e a p r o g r a m i c o nw i l l b e c r e a t e d . d o u b l e c l i c k o n i t , a p r o g r a m e d i t o r

w i l l b e o p e n , e r a s e t h e c o d e a n d t y p e y o u r p r o g r a m

c o d i n g . C o m p i l e : c l i c k t h e c o m p i l e b u t t o n o n t h el e f t o f t h e w i n d o w o r r i g h t c l i c k o n t h e c l a s s i c o n

a n d s e l e c t c o m p i l e f r o m t h e m e n u o p t i o n s . E x e c u t e :

R i g h t c l i c k o n t h e c l a s s i c o n a n d s e l e c t n e w c l a s sn a m e o p t i o n . A d i a l o g u e b o x a p p e a r s t y p e t h e n a m e

o f t h e o b j e c t . A o b j e c t i c o n w i l l b e c r e a t e d a t t h e

b o t t o m . R i g h t c l i c k o n t h e o b j e c t i c o n a n d s e l e c tt h e m e t h o d w e w a n t t o e x e c u t e .

Q. The two types of Java programs/applications are? [2007]A n s : T h e t w o t y p e s o f J a v a A p p l i c a t i o n s a r e

' I n t e r n e t A p p l e t s ' a n d ' S t a n d a l o n e a p p l i c a t i o n ' .

Q. State the distinguishing features of Java and C++?

A n s : ( i ) J a v a d o e s n o t s u p p o r t o p e r a t o r

o v e r l o a d i n g . ( i i ) J a v a d o e s n o t u s e p o i n t e r s . ( i i i )T h e r e a r e n o h e a d e r f i l e s i n J a v a . ( i v ) J a v a d o e s

n o t h a v e t e m p l a t e c l a s s e s a s i n C + + .Q. State the differences between Syntax errors and Logical errors.

A n s : T h e c o m p i l e r c a n o n l y t r a n s l a t e a p r o g r a m i f

t h e p r o g r a m i s s y n t a c t i c a l l y c o r r e c t ; o t h e r w i s e

t h e c o m p i l a t i o n f a i l s a n d y o u w i l l n o t b e a b l e t o


3/53

r u n y o u r p r o g r a m . S y n t a x r e f e r s t o t h e s t r u c t u r e o f y o u r p r o g r a m a n d t h e r u l e s a b o u t t h a t s t r u c t u r e . T h e

s e c o n d t y p e o f e r r o r i s a r u n - t i m e e r r o r , s o - c a l l e d

b e c a u s e t h e e r r o r d o e s n o t a p p e a r u n t i l y o u r u n

t h e p r o g r a m . I n J a v a , r u n - t i m e e r r o r s o c c u r w h e n

t h e i n t e r p r e t e r i s r u n n i n g t h e b y t e c o d e a n ds o m e t h i n g g o e s w r o n g .Q. "Object is an instance of a class", explain

A n s : O b j e c t o f a c l a s s c o n t a i n s d a t a a n d f u n c t i o n s

p r o v i d e d i n a c l a s s . i t p o s s e s s e s a l l t h e f e a t u r e s

o f a c l a s s . H e n c e o b j e c t i s t e r m e d a s i n s t a n c e o f a

c l a s s .

Q. Name four basic features of JAVA.A n s : B a s i c f e a t u r e s o f J a v a a s f o l l o w s : i ) I t i s a n

o b j e c t o r i e n t e d l a n g u a g e . i i ) J a v a p r o g r a m i s b o t h

c o m p i l e d a n d i n t e r p r e t e d . i i i ) J a v a p r o g r a m c a n b ea p p l i c a t i o n o r a p p l e t . i v ) j a v a i s c a s e s e n s i t i v e

l a n g u a g e , i . e . i t d i s t i n g u i s h e d u p p e r a n d l o w e r c a s el e t t e r s .

Q. Differentiate between Compiler and Interpreter.

A n s : C o m p i l e r c o n v e r t s o u r c e c o d e t o m a c h i n el a n g u a g e w h o l e a t a t i m e . I n t e r p r e t e r c o n v e r t s

p r o g r a m f r o m h i g h l e v e l l a n g u a g e t o m a c h i n e l e v e l

l a n g u a g e l i n e b y l i n e o r s t a t e m e n t b y s t a t e m e n t .Q. Java uses compiler as well as interpreter, explain.

A n s : J a v a c o m p i l e r c o n v e r t s J a v a s o u r c e c o d e t o

b y t e c o d e . T h i s b y t e c o d e i s f u r t h e r c o n v e r t e di n t o m a c h i n e c o d e t o m a k e i t a p p l i c a b l e f o r t h e

s p e c i f i c p l a t f o r m b y u s i n g i n t e r p r e t e r .

Q. Differentiate between Source code andByte code.A n s : S o u r c e c o d e i s t h e p r o g r a m d e v e l o p e d i n J a v a

L a n g u a g e , w h i c h i s i n p u t t o a c o m p u t e r t h r o u g ht h e k e y b o a r d . C o m p i l e r c o n v e r t s s o u r c e c o d e t o b y t e

c o d e f o r i n t e r p r e t a t i o n .

Q. Differentiate between Testing and Debugging.

A n s : T e s t i n g i s t h e p r o c e s s o f c h e c k i n g p r o g r a m

l o g i c m a n u a l l y t o e n s u r e w h e t h e r i t c o n t a i n s a n ye r r o r o r n o t . D e b u g g i n g i s t h e p r o c e s s o f r e m o v i n g

e r r o r s f r o m a p r o g r a m .E l e m e n t a r y C o n c e p t s o f O b j e c t & C l a s s

[ICSE Syllabus on this Topic]Modeling entities and their behavior by objects.

A class as a specification of objects and as an objectfactory, computation


4/53

as message passing/function call between objects (many example should bedone to

I C S E B l u e J

T h e o r y h t t p : / / w w w . a m


r g . i n / m a t e r i a l s / i c se / j t h e o r y . h t m 2o f

2 4 8

/ 2 0

/ 2 0

1 1

1 1 :2 7

P M

illustrate this). Object encapsulate state (attribute) and have behaviors(functions). Class as a user definedtype.

Q. What is an Object? [2006]A n s : A n O b j e c t i s a n i d e n t i f i a b l e e n t i t y w i t h s o m e

c h a r a c t e r i s t i c s a n d b e h a v i o r . E . g . t a k e a c l a s s

' C a r ' . A c a r c l a s s h a s c h a r a c t e r i s t i c s l i k e c o l o u r ,g e a r s , p o w e r , l e n g t h e t c . n o w w e c r e a t e t h e o b j e c t

o f t h a t c l a s s ' C a r ' n a m e l y ' I n d i c a ' .

Q. What is OOP? What are the features/concepts in OOP's? [2007]ORName any twoOOP'S principles. [2005]

A n s : T h e O b j e c t O r i e n t e d P r o g r a m m i n g P a r a d i g m i s

t h e l a t e s t i n t h e s o f t w a r e d e v e l o p m e n t a n d t h em o s t a d o p t e d o n e i n t h e p r o g r a m m i n g d e v e l o p m e n t .

T h e P a r a d i g m m e a n s o r g a n i s i n g p r i n c i p l e o f a

p r o g r a m . I t i s a n a p p r o a c h t o p r o g r a m m i n g . T h ec o n c e p t s o f O O P ' s a r e : ( 1 ) D a t a A b s t r a c t i o n ( 2 )

D a t a E n c a p s u l a t i o n ( 3 ) M o d u l a r i t y ( 4 ) I n h e r i t a n c e ( 5 )P o l y m o r p h i s m .

Q. Explain all the Concepts of OOP's?

A n s : A b s t r a c t i o n : I t r e f e r s t o t h e a c t o f

r e p r e s e n t i n g e s s e n t i a l f e a t u r e s w i t h o u t i n c l u d i n g

t h e b a c k g r o u n d d e t a i l s o r e x p l a n a t i o n .E n c a p s u l a t i o n : I t i s t h e w a y o f c o m b i n i n g b o t h d a t a

a n d t h e f u n c t i o n t h a t o p e r a t e s o n t h e d a t a u n d e r as i n g l e u n i t . M o d u l a r i t y : I t i s t h e p r o p e r t y o f a

s y s t e m t h a t h a s b e e n d e c o m p o s e d i n t o a s e t o f

c o h e s i v e a n d l o o s e l y c o u p l e m o d u l e s . I n h e r i t a n c e :

I t i s t h e c a p a b i l i t y o f o n e c l a s s o f t h i n g t o


5/53

i n h e r i t p r o p e r t i e s f r o m a n o t h e r c l a s s . P o l y m o r p h i s m :I t i s t h e a b i l i t y f o r a m e s s a g e o r d a t a t o b e

p r o c e s s e d i n m o r e t h e n o n e f o r m .

Q. What are the advantages of OOP's?

A n s : ( 1 ) E l i m i n a t i o n o f r e d u n d a n t c o d i n g s y s t e m

a n d u s a g e o f e x i s t i n g c l a s s e s t h r o u g h i n h e r i t a n c e .( 2 ) P r o g r a m c a n b e d e v e l o p e d b y s h a r i n g e x i s t i n gm o d u l e s . ( 3 ) P o s s i b i l i t i e s o f m u l t i p l e i n s t a n c e o f

a n o b j e c t s w i t h o u t a n y i n t e r f e r e n c e . ( 4 ) S e c u r i t y o f

d a t a v a l u e s f r o m o t h e r s e g m e n t o f t h e p r o g r a m

t h r o u g h d a t a h i d i n g .

Q. What is Class? How Object is related to the Class?

A n s : A C l a s s r e p r e s e n t a s e t o f O b j e c t s t h a t s h a r ec o m m o n c h a r a c t e r i s t i c s a n d b e h a v i o r . O b j e c t s

a r e i n s t a n c e o f a c l a s s . T h e O b j e c t r e p r e s e n t s t h e

a b s t r a c t i o n r e p r e s e n t a t i o n b y t h e c l a s s i n t h e r e a ls e n s e .

Q. What is the need of a class in Java?A n s : C l a s s e s i n J a v a a r e n e e d e d t o r e p r e s e n t r e a l -

w o r l d e n t i t i e s , w h i c h h a v e d a t a t y p e p r o p e r t i e s .

C l a s s e s p r o v i d e c o n v e n i e n t m e t h o d s f o r p a c k i n gt o g e t h e r a g r o u p o f l o g i c a l r e l a t e d d a t a i t e m s a n d

f u n c t i o n s t h a t w o r k o n t h e m . I n j a v a t h e d a t a i t e m s

a r e c a l l e d f i e l d s & t h e f u n c t i o n s a r e c a l l e dm e t h o d s .

Q. What are Methods? How are these related to an Objects?

A n s : A M e t h o d i s a n o p e r a t i o n a s s o c i a t e d t o a nO b j e c t . T h e b e h a v i o r o f a n O b j e c t i s r e p r e s e n t e d

t h r o u g h a s s o c i a t e d f u n c t i o n , w h i c h a r e c a l l e d

M e t h o d s .Q. Point out the differences between Procedural Programming and Object Oriented

Programming.A n s : P r o c e d u r a l p r o g r a m m i n g a i m s m o r e a t

p r o c e d u r e s . T h e e m p h a s i s i s a d o i n g t h i n g s r a t h e r

t h e n t h e d a t a b e i n g u s e d . I n p r o c e d u r a l P r o g r a m m i n g

p a r a d i n g d a t a a r e s h a r e d a m o n g a l l t h e

f u n c t i o n s p a r t i c i p a t i n g t h e r e b y r i s k i n g d a t a s a f e t ya n d s e c u r i t y . O b j e c t O r i e n t e d P r o g r a m m i n g i s b a s e d

o n p r i n c i p l e s o f d a t a h i d i n g , a b s t r a c t i o n ,i n h e r i t a n c e a n d p o l y m o r p h i s m . I t i m p l e m e n t s

p r o g r a m s u s i n g c l a s s e s a n d o b j e c t s , I n O O P ' s d a t a

a n d p r o c e d u r e b o t h g i v e n e q u a l i m p o r t a n c e . D a t a


6/53

a n d f u n c t i o n s a r e e n c a p s u l a t e d t o e n s u r e d a t as a f e t y a n d s e c u r i t y .

Q. What is an abstraction?

A n s : A n a b s t r a c t i o n i s a n a m e d c o l l e c t i o n o f

a t t r i b u t e s a n d b e h a v i o r s r e q u i r e d t o r e p r e s e n t a n

e n t i t y o r c o n c e p t f o r s o m e p a r t i c u l a r p r o b l e md o m a i n .Q. What is

and how it is useful in Java. [2008]

A n s : I t i s p r o c e s s b y w h i c h o b j e c t s o f o n e c l a s s

a c q u i r e t h e p r o p e r t i e s o f o b j e c t s o f a n o t h e r

c l a s s . I n h e r i t a n c e s u p p o r t s t h e c o n c e p t s o f h i e r a r c h i c a l r e p r e s e n t a t i o n . I n O O P t h e c o n c e p t s o f

i n h e r i t a n c e p r o v i d e s t h e i d e a o f r e u s a b i l i t y .

Q. What role does polymorphism play as java feature?A n s : I t m e a n t h e a b i l i t y t o t a k e m o r e t h a n o n e

f o r m . F o r e x a m p l e , a n o p e r a t i o n , m a n y t y p e s o f d a t a u s e d i n t h e o p e r a t i o n .

Q. What is Data hiding?



r g . i n / m a t e r i a l s / i c se / j t h e o r y . h t m 3

o f

2 4 8/ 2 0

/ 2 0

1 11 1 :

2 7P M

A n s : D a t a H i d i n g m e a n s r e s t r i c t i n g t h e a c c e s s i b i l i t y

o f d a t a a s s o c i a t e d w i t h a n o b j e c t i n s u c h a w a y

t h a t i t c a n b e u s e d o n l y t h r o u g h t h e m e m b e r

m e t h o d s o f t h e o b j e c t .Q. What are nested classes?

A n s : I t i s p o s s i b l e t o d e f i n e a c l a s s w i t h i n a n o t h e rc l a s s , s u c h c l a s s e s a r e k n o w n a s n e s t e d c l a s s e s .

A n e s t e d c l a s s h a s a c c e s s t o t h e m e m b e r s

i n c l u d i n g p r i v a t e m e m b e r s o f t h e c l a s s i n w h i c h i t


7/53

i s n e s t e d . H o w e v e r t h e e n c l o s i n g c l a s s n o t h a v ea c c e s s t o t h e m e m b e r s o f t h e n e s t e d c l a s s .

Q. Differentiate between

and

class. [2008]A n s : B A S E C L A S S - A c l a s s f r o m w h i c h a n o t h e r

c l a s s i n h e r i t s ( A l s o c a l l e d S U P E R C L A S S ) D E R I V E D

C L A S S - A c l a s s i n h e r i t i n g p r o p e r t i e s f r o m a n o t h e r

c l a s s . ( A l s o c a l l e d S U B C L A S S )

C l a s s a s t h e B a s i s o f a l l C o m p u t a t i o n

[ICSE Syllabus on this Topic]Objects encapsulates state and behavior -numerous example, member variables, attributes or features.Variable define

states, Member functions/operation/methods/messages defines behaviors.

Class asabstractions for set of objects, class as an object factory, concept of type,primitive data types, compositedata types. Var iable declaration for both types,

diffe rence between the two types. Objects as instance of a class. Modeling bycomposition.

Q. What are keywords? can keywords be used as a identifiers?

A n s : K e y w o r d s a r e t h e w o r d s t h a t c o n v e y a s p e c i a lm e a n i n g t o t h e l a n g u a g e c o m p i l e r . N o , k e y w o r d s

c a n n e v e r b e u s e d a s i d e n t i f i e r s .

Q. What is an identifier? What is the identifier formatting rule of Java? OR What arethe rules for naming a variable?

A n s : I d e n t i f i e r s a r e n a m e s g i v e n t o d i f f e r e n t p a r t s

o f a p r o g r a m e . g . v a r i a b l e s , f u n c t i o n s , c l a s s e s e t c .T h e i d e n t i f i e r s i n J a v a . ( i ) C a n c o n t a i n s a l p h a b e t s ,

d i g i t s , d o l l a r s i g n a n d u n d e r s c o r e . ( i i ) M u s t n o t

s t a r t w i t h a d i g i t . ( i i i ) C a n n o t b e a J a v ak e y w o r d s . ( i v ) C a n h a v e a n y l e n g t h a n d a r e c a s e -

s e n s i t i v e .Q. Why keyword is different from identifiers?

A n s : K e y w o r d s a r e p r e d e f i n e s e t s o f w o r d s t h a t

h a v e a s p e c i a l m e a n i n g f o r t h e J a v a c o m p i l e r .

I d e n t i f i e r s o n t h e o t h e r h a n d a r e c r e a t e d b y J a v a

p r o g r a m m e r s i n o r d e r t o g i v e n a m e s t o v a r i a b l e s ,f u n c t i o n , c l a s s e s e t c .

Q. State the difference between Token and Identifier.[2008]A n s : T h e s m a l l e s t i n d i v i d u a l u n i t o f a p r o g r a m i s

k n o w n a s T o k e n . T h e f o l l o w i n g T o k e n s a r e a v a i l a b l e

i n J a v a : K e y w o r d s , I d e n t i f i e r s , L i t e r a l s ,

P u n c t u a t i o n s , O p e r a t o r s . I d e n t i f i e r s a r e n a m e s g i v e n


8/53

t o d i f f e r e n t p a r t s o f a p r o g r a m e . g . v a r i a b l e s ,f u n c t i o n s , c l a s s e s e t c . T h e i d e n t i f i e r s i n J a v a .

Q. What are literals? How many types of integer literals are avail able in

Java?

A n s : A l i t e r a l i s s e q u e n c e o f c h a r a c t e r s u s e d i n a

p r o g r a m t o r e p r e s e n t a c o n s t a n t v a l u e . F o r e x a m p l e' A ' i s a l i t e r a l t h a t r e p r e s e n t s t h e v a l u e A o f t y p ec h a r , a n d 1 7 L i s a l i t e r a l t h a t r e p r e s e n t s t h e

n u m b e r 1 7 a s v a l u e o f t y p e l o n g . D i f f e r e n t t y p e s o f

l i t e r a l s a v a i l a b l e i n J a v a , t h e y a r e : I n t e g e r l i t e r a l ,

F l o a t l i t e r a l , B o o l e a n l i t e r a l , C h a r a c t e r l i t e r a l ,

S t r i n g l i t e r a l a n d n u l l l i t e r a l .

Q. What is an integer constant? Write integer forming rule of Java.A n s : I n t e g e r c o n s t a n t s a r e w h o l e n u m b e r s w i t h o u t

a n y d e c i m a l p a r t . T h e r u l e f o r f o r m i n g a n

i n t e g e r c o n s t a n t s i s : A n i n t e g e r c o n s t a n t m u s t h a v ea t l e a s t o n e d i g i t a n d c a n n o t c o n t a i n a d e c i m a l

p o i n t . I t m a y c o n t a i n s + o r - s i g n . A n u m b e r w i t h n os i g n i s i n t e r p r e t e d t o b e p o s i t i v e .

Q. What do you mean by Escape sequence and name few escape sequences in Java?

A n s : J a v a h a v e c e r t a i n n o n g r a p h i c c h a r a c t e r s( n o n g r a p h i c c h a r a c t e r s a r e t h o s e c h a r a c t e r s t h a t

c a n n o t b e t y p e d d i r e c t l y f r o m k e y b o a r d e . g .

b a c k s p a c e , t a b , c a r r i a g e r e t u r n e t c . ) . T h o s en o n g r a p h i c c h a r a c t e r c a n b e r e p r e s e n t e d b y e s c a p e

s e q u e n c e . A n e s c a p e s e q u e n c e i s r e p r e s e n t e d b y

b a c k s l a s h f o l l o w e d b y o n e o r m o r e c h a r a c t e r . T h ef e w e s c a p e s e q u e n c e c h a r a c t e r s a r e : \ n f o r n e w

l i n e , \ t f o r H o r i z o n t a l T a b , \ v f o r V e r t i c a l T a b , \ b

f o r B a c k s p a c e , \ " f o r D o u b l e Q u o t e s e t c .Q. How many integer constants are allowed in Java? How are they written?





o f2 4 8

/ 2 0/ 2 0

1 1

1 1 :


9/53

2 7P M

A n s : J a v a a l l o w s t h r e e t y p e s o f i n t e g e r c o n s t a n t s :

O c t a l ( b a s e 8 ) , D e c i m a l ( b a s e 1 0 ) , a n d

H e x a d e c i m a l ( b a s e 1 6 ) . A n O c t a l i n t e g e r m u s t b e

s t a r t e d w i t h a z e r o ' 0 ' , a H e x a d e c i m a l i n t e g e rs t a r t s w i t h a ' 0 X ' , a l l o t h e r s a r e t r e a t e d a s d e c i m a li n t e g e r c o n s t a n t .

Q. What is meant by a floating constant in Java? How many ways can a floating

constant be represented into?

A n s : F l o a t i n g c o n s t a n t s a r e r e a l n u m b e r s . A

f l o a t i n g c o n s t a n t c a n e i t h e r b e a f r a c t i o n a l o r i n

e x p o n e n t f o r m .Q. Differentiate between Integer and Floating type constants.

A n s : I n t e g e r c o n s t a n t s a r e t h e w h o l e n u m b e r s

( w i t h o u t d e c i m a l p o i n t s ) . e . g . 1 2 3 1 . F l o a t i n gp o i n t c o n s t a n t s a r e f r a c t i o n a l n u m b e r s ( n u m b e r w i t h

d e c i m a l p o i n t s ) . e . g . 1 4 . 2 3 5 6Q. Write the following real constants into fractional form: 0.113E04, 0.417E-04, 0.4E-05,

0.123E02

A n s : 0 . 1 1 3 E 0 4 b e c o m e s 1 1 3 0 , 0 . 4 1 7 E - 0 4 b e c o m e s. 0 0 0 0 4 1 7 , 0 . 4 E - 0 5 b e c o m e s . 0 0 0 0 0 4 ,

0 . 1 2 3 E 0 2 b e c o m e s 1 2 . 3

Q. What is a type or 'Data Type'? How this term is related to programming?A n s : A t y p e o r d a t a t y p e r e p r e s e n t s a s e t o f

p o s s i b l e v a l u e s . W h e n w e s p e c i f y t h a t a v a r i a b l e

h a s c e r t a i n t y p e , w e a r e s a y i n g w h a t v a l u e s t h ee x p r e s s i o n c a n h a v e . F o r e x a m p l e t o s a y t h a t a

v a r i a b l e i s o f t y p e i n t s a y s t h a t i n t e g e r v a l u e s i n a

c e r t a i n r a n g e c a n b e s t o r e d i n t h a t v a r i a b l e .Q. What is primitive data type? Name its different types.

A n s : P r i m i t i v e d a t a t y p e s a r e t h o s e t h a t a r e n o tc o m p o s e d o f o t h e r d a t a t y p e s . N u m e r i c

I n t e g r a l , F r a c t i o n a l , c h a r a c t e r a n d b o o l e a n a r e

d i f f e r e n t p r i m i t i v e d a t a t y p e s .

Q. State the two kind on data types? [2006]

A n s : T h e t w o t y p e s o f d a t a t y p e s a r e : P r i m i t i v e a n dn o n - p r i m i t i v e / c o m p o s i t e / u s e r d e f i n e d a t a t y p e s .

T h e p r i m i t i v e d a t a t y p e s a r e : b y t e , s h o r t , i n t , l o n g ,f l o a t , d o u b l e , c h a r a n d B o o l e a n . T h e n o n -

p r i m i t i v e / r e f e r e n c e d a t a t y p e s a r e : c l a s s , a r r a y a n d

i n t e r f a c e .


10/53

Q. Write down the names of three primitive and three non-primitive/reference datatypes in Java/BlueJ.

A n s : T h e p r i m i t i v e d a t a t y p e s a r e : b y t e , s h o r t , i n t ,

l o n g , f l o a t , d o u b l e , c h a r a n d B o o l e a n . T h e n o n -

p r i m i t i v e / r e f e r e n c e d a t a t y p e s a r e : c l a s s , a r r a y a n d

i n t e r f a c e .Q. How many bytes occupied by the following data types: byte, short, int, long, float,double, char, boolean.

A n s : c h a r - 2 b y t e , b y t e - 1 b y t e , s h o r t - 2 b y t e s , i n t - 4

b y t e s , l o n g - 8 b y t e s , f l o a t - 4 b y t e s , d o u b l e - 8

b y t e s , b o o l e a n - J a v a r e s e r v e 8 b i t s b u t o n l y u s e 1

b i t .

Q. What is the range of the following data types: byte, short, int, long, float, double,char, boolean.

A n s : b y t e - > - 1 2 8 t o 1 2 7 s h o r t - > - 3 2 7 6 8 t o 3 2 7 6 7 i n t -

> - 231

to 231

-1l o n g - > - 2

63to 2

63

-1f l o a t - > - 3 . 4 x 1 038

t o 3 . 4 x 1 0

38d o u b l e - > - 1 . 7 x 1 0

308

t o 1 . 7 x 1 0308

c h a r - > 0 t o 6 5 5 3 6 b o o l e a n - > t r u e o r f a l s eQ. What is the largest and smallest value for floating point primitive data types float?

A n s : T h e s m a l l e s t v a l u e i s - 3 . 4 E + 3 8 a n d l a r g e s t

v a l u e s i s 3 . 4 E + 3 8 o f f l o a t i n g p o i n t d a t a t y p e .

Q. What is Token? What are the tokens available in Java? [2008]

A n s : T h e s m a l l e s t i n d i v i d u a l u n i t o f a p r o g r a m i sk n o w n a s T o k e n . T h e f o l l o w i n g T o k e n s a r e a v a i l a b l e

i n J a v a : - K e y w o r d s , I d e n t i f i e r s , L i t e r a l s ,P u n c t u a t i o n s , O p e r a t o r s .

Q. What do you mean by variables? [2006]


11/53

A n s : A v a r i a b l e i s a n a m e d m e m o r y l o c a t i o n , w h i c hh o l d s a d a t a v a l u e o f a p a r t i c u l a r d a t a t y p e s .

E . g . d o u b l e p ;

Q. What do you mean by variables? What do you mean by dynamic initialization of a

variable?

A n s : A v a r i a b l e i s a n a m e d m e m o r y l o c a t i o n , w h i c hh o l d s a d a t a v a l u e o f a p a r t i c u l a r d a t a t y p e s .W h e n a m e t h o d o r f u n c t i o n s i s c a l l e d a n d t h e r e t u r n

v a l u e i s i n i t i a l i s e t o a v a r i a b l e i s c a l l e d d y n a m i c

i n i t i a l i s a t i o n . e x a m p l e d o u b l e p = M a t h . p o w ( 2 , 3 ) ;

Q. What is the function of an operator?

I C S E B l u e J

T h e o r y h t t p : / / w w w . a mi t a b h s i r k i c l a s s e s . o


e / j t h e o r y . h t m 5o f

2 4 8/ 2 0

/ 2 0

1 11 1 :

2 7

P MA n s : O p e r a t o r s a r e s p e c i a l s y m b o l s t h a t r e p r e s e n t

o p e r a t i o n s t h a t c a n b e c a r r i e d o u t o n

v a r i a b l e s , c o n s t a n t s o r e x p r e s s i o n s .Q. What do you mean by operator and write the name of all operators given in your

textbook.

A n s : T h e o p e r a t i o n s a r e r e p r e s e n t e d b y o p e r a t o r sa n d t h e o b j e c t o f t h e o p e r a t i o n s a r e r e f e r r e d t o

a s o p e r a n d s . T h e t y p e s o f O p e r a t o r s a v a i l a b l e i nJ a v a a r e : 1 . A r i t h m e t i c 2 . I n c r e m e n t / D e c r e m e n t 3 .

R e l a t i o n a l 4 . L o g i c a l 5 . S h i f t 6 . B i t w i s e 7 .

A s s i g n m e n t 8 . C o n d i t i o n a l 9 . [ ] o p e r a t o r 1 0 . n e w

o p e r a t o r 1 1 . ( t y p e ) c a s t O p e r a t o r 1 2 . ( ) o p e r a t o r .

1 3 . d o t o p e r a t o r .Q. What are arithmetic operators?

A n s : A r i t h m e t i c a l o p e r a t o r s a r e u s e d f o r v a r i o u sm a t h e m a t i c a l c a l c u l a t i o n s . T h e r e s u l t o f a n

a r i t h m e t i c a l e x p r e s s i o n i s a n u m e r i c a l v a l u e s .

A r i t h m e t i c a l o p e r a t o r s a r e o f f o l l o w i n g t y p e s :

U n a r y a n d B i n a r y o p e r a t o r s .


12/53

Q. Write major difference between the unary and binary operators?A n s : T h e o p e r a t o r s t h a t a c t s o n o n e o p e r a n d a r e

r e f e r r e d t o a s U n a r y O p e r a t o r . T h e r e a r e t w o

U n a r y o p e r a t o r s U n a r y + o p e r a t o r a n d U n a r y -

o p e r a t o r . T h e o p e r a t o r s t h a t a c t s u p o n t w o

o p e r a n d s a r e r e f e r r e d t o a s B i n a r y O p e r a t o r . T h eB i n a r y O p e r a t o r s a r e A d d i t i o n ( + ) , S u b t r a c t i o n ( - ) ,M u l t i p l i c a t i o n ( * ) , D i v i s i o n ( / ) a n d M o d u l u s ( % ) .

Q. What is increment operator? What are postfix and prefix increment operators?

A n s : T h e ' + + ' o p e r a t o r i s c a l l e d i n c r e m e n t

o p e r a t o r . T h e i n c r e m e n t o p e r a t o r s a d d 1 t o i t s

o p e r a n d . T h e s e a r e t w o t y p e s ( i ) P r e f i x a n d ( i i )

P o s t f i x T h e p r e f i x v e r s i o n c o m e s b e f o r e t h eo p e r a n d f o r e . g . + + a , w h e r e a s p o s t f i x c o m e s a f t e r

t h e o p e r a n d e . g . a + +

Q. Find the value of x after evaluating x += x++ + --x + 4 where x=3 before theevaluation. Explain your answer.

A n s : R e s u l t i s 1 3 , b e c a u s e x + + i s 3 , - - x i s 2 + 4t h e a n s w e r i s 9 a d d t h i s w i t h x t h a t i s 3 i t

b e c o m e s 1 2 a n d d u e t o p r e i n c r e m e n t o f x + + t h e

r e s u l t b e c o m e s 1 3 .Q. What do you mean by Relational Operators.

A n s : R e l a t i o n a l o p e r a t o r s a r e u s e d t o d e t e r m i n e

t h e r e l a t i o n s h i p b e t w e e n d i f f e r e n t o p e r a n d s . T h e s ea r e u s e d i n w o r k o f c o m p r e s s i o n a l s o . T h e r e l a t i o n a l

e x p r e s s i o n ( c o n d i t i o n ) r e t u r n s 0 i f t h e r e l a t i o n i s

f a l s e a n d r e t u r n 1 i f t h e r e l a t i o n i s t r u e . < ( l e s st h e n ) , > ( g r e a t e r t h e n ) , < = ( l e s s t h e n e q u a l s t o ) ,

> = ( g r e a t e r t h e n e q u a l s t o ) , = = ( e q u a l s t o ) , ! = ( n o t

e q u a l s t o ) .Q. What is Logical operators?

A n s : T h e l o g i c a l o p e r a t o r s c o m b i n e t h e r e s u l t o f o rm o r e t h e n t w o e x p r e s s i o n s . T h e m o d e o f

c o n n e c t i n g r e l a t i o n s h i p i n t h e s e e x p r e s s i o n s r e f e r s

a s l o g i c a l a n d t h e e x p r e s s i o n s a r e c a l l e d l o g i c a l

e x p r e s s i o n . T h e l o g i c a l e x p r e s s i o n r e t u r n s 1 i f t h e

r e s u l t i s t r u e o t h e r w i s e 0 r e t u r n s . T h e l o g i c a lo p e r a t o r s p r o v i d e d b y J a v a a r e & & L o g i c a l A N D , | |

L o g i c a l O R , ! L o g i c a l N O T .Q. What do you man by Assignment Statement or Assignment Operator?

A n s : A s s i g n m e n t o p e r a t o r i s r e p r e s e n t b y s y m b o l

' = ' . I t t a k e s t h e v a l u e o n t h e r i g h t a n d s t o r e s i t i n


13/53

t h e v a r i a b l e o n t h e l e f t s i d e . f o r e x a m p l e x = y +3 0

Q. What do you mean by Shift operators? OR Differentiate between Shift LEFT and

Shift RIGHT operators.

A n s : A S h i f t o p e r a t o r s p e r f o r m s b i t m a n i p u l a t i o n o n

d a t a b y s h i f t i n g t h e b i t s o f i t s f i r s t o p e r a n d r i g h tt o l e f t . T h e s h i f t o p e r a t o r s a v a i l a b l e i n J a v a a r e : ( 1 )> > s h i f t b i t s o f r i g h t b y d i s t a n c e . ( s i g n e d

s h i f t i n g ) ( 2 ) < < s h i f t b i t s o f l e f t b y d i s t a n c e .

( s i g n e d s h i f t i n g ) ( 3 ) > > > s h i f t b i t s o f r i g h t b y

d i s t a n c e ( u n s i g n e d s h i f t i n g )

Q. Differentiate between Shift LEFT and Shift RIGHT operators.

A n s : S h i f t L E F T ( < < ) o p e r a t r s h i f t s t h e b i t p a t t e r no f t h e o p e r a n d t o w a r d s l e f t b y d e f i n e d n u m b e r o f

b i t s . S h i f t R I G H T ( > > ) o p e r a t o r s h i f t s t h e b i t p a t t e r n

o f t h e o p e r a n d t o w a r d s r i g h t b y d e f i n e d n u m b e r o f b i t s . e . g . 1 3 > > 2 i s 3 b i n a r y v a l u e o f 1 3 i s 1 1 0 1 > > 2 i s

0 0 1 1 i s e q u i v a l e n t t o 3 . S i m i l a r l y L E F T s h i f t ( < < )o p e r a t o r i s a l s o w o r k .

Q. What do you mean by Bitwise operators?

A n s : T h e B i t w i s e o p e r a t i o n s a r e p e r f o r m e d b yB i t w i s e o p e r a t o r . T h e B i t w i s e o p e r a t i o n s c a l c u l a t e

e a c h b i t o f t h e i r r e s u l t b y c o m p a r i n g t h e

c o r r e s p o n d i n g b i t s o f t h e t w o o p e r a n d s . ( a ) T h e A N Do p e r a t o r & ( b ) T h e O R o p e r a t o r | ( c ) T h e X O R

o p e r a t o r ^ ( d ) T h e c o m p l i m e n t o p e r a t o r ~




o f2 4 8

/ 2 0

/ 2 0

1 1

1 1 :2 7

P MQ. Illustrate '?' operator with an example? [2009]

A n s : I t i s a c o n d i t i o n a l o p e r a t o r , t h a t s t o r e s a

v a l u e d e p e n d i n g u p o n a c o n d i t i o n . T h i s o p e r a t o r i s

a l s o k n o w n a s t e r n a r y o p e r a t o r . T h e s y n t a x f o r t h i s


14/53

o p e r a t o r i s e x p r e s s i o n 1 ? e x p r e s s i o n 2 : e x p r e s s i o n 3 .a n d t h e e x a m p l e i s b o n u s = s a l e s > 1 5 0 0 0 ? 2 5 0 : 5 0 ;

Q. What is the purpose of new operator?

[2006]

A n s : W e c a n u s e n e w o p e r a t o r t o c r e a t e a n e w

o b j e c t s o r n e w a r r a y . E x . m y C l a s s o b j = n e wm y C l a s s ( ) ; i n t a r r [ ] = n e w i n t [ 5 ] ;Q. What do you mean by precedence? Illustrate with the help of example.

A n s : P r e c e d e n c e i s t h e o r d e r i n w h i c h a p r o g r a m

e v a l u a t e s t h e o p e r a t i o n s i n a f o r m u l a o r

e x p r e s s i o n . A l l o p e r a t o r s h a v e p r e c e d e n c e v a l u e . A n

o p e r a t o r w i t h h i g h e r p r e c e d e n c e v a l u e i s e v a l u a t e d

f i r s t t h e n t h e o p e r a t o r h a v i n g l o w e r p r e c e d e n c ev a l u e . c o n s i d e r t h e f o l l o w i n g e x a m p l e x = 5 + 4

* 6 ; T h e v a l u e o f t h i s e x p r e s s i o n i s 2 9 n o t 5 4 o r 3 4 .

M u l t i p l i c a t i o n h a s b e e n p e r f o r m e d f i r s t i n t h i se x p r e s s i o n .

Q. What is operands?A n s : A n o p e r a t o r a c t s o n d i f f e r e n t d a t a

i t e m s / e n t i t i e s c a l l e d o p e r a n d s .

Q. What do you mean by constant? How you declare a variable as constant variables.A n s : T h e m e m o r y v a r i a b l e s / l o c a t i o n s w h o s e v a l u e s

c a n n o t b e c h a n g e d w i t h i n t h e p r o g r a m i s

c a l l e d c o n s t a n t s . T h e k e y w o r d f i n a l m a k e s a v a r i a b l ea s c o n s t a n t s .

Q. Which class is used for using different mathematical function in Java program?

[2007]A n s : T h e c l a s s u s e d f o r d i f f e r e n t m a t h e m a t i c a l

f u n c t i o n s i n J a v a i s j a v a . l a n g . M a t h

Q. Write down the equivalent expression for the mathematical expression (a) (cos x/tan-1

x)+x (b) |ex

- x|

A n s : ( M a t h . c o s ( x ) / M a t h . a t a n ( x ) ) + x a n d

M a t h . a b s ( M a t h . e x p ( x ) - x )

Q. What is the difference between these two function Math.ceil() and Math.rint(), explainwith example.

A n s : M a t h . c e i l ( ) t h i s f u n c t i o n r e t u r n s t h e s m a l l e s tw h o l e n u m b e r g r e a t e r t h e n o r e q u a l t o t h e

g i v e n n u m b e r . e . g . M a t h . c e i l ( 1 2 . 8 5 ) g i v e s o u t p u t 1 3

a n d M a t h . c e i l ( 1 2 . 3 5 ) a l s o g i v e s o u t p u t 1 3 . W h e r e a s

t h e M a t h . r i n t ( ) r e t u r n s t h e r o u n d u p n e a r e s t i n t e g e r


15/53

v a l u e . e . g . M a t h . r i n t ( 1 2 . 8 5 ) g i v e s o u t p u t 1 3b u t M a t h . r i n t ( 1 2 . 3 5 ) g i v e s o u t p u t 1 2 .

Q. What do you mean by type conversion? What is the difference between implicit and

explicit type conversion explainwith example.

A n s : T h e p r o c e s s o f c o n v e r t i n g o n e p r e d e f i n e d t y p e

i n t o a n o t h e r i s c a l l e d T y p e C o n v e r s i o n . A i m p l i c i tt y p e c o n v e r s i o n i s a c o n v e r s i o n p e r f o r m e d b y t h ec o m p i l e r . T h e J a v a c o m p i l e r c o n v e r t s a l l o p e r a n d s

u p t o t h e t y p e o f t h e l a r g e s t o p e r a n d . T h i s i s a l s o

k n o w n a s t y p e p r o m o t i o n . e . g . ' c ' - 3 2 i s c o n v e r t e d t o

i n t t y p e . W h e r e a s a n e x p l i c i t t y p e c o n v e r s i o n i s

u s e r d e f i n e d t h a t f o r c e s a n e x p r e s s i o n t o b e o f

s p e c i f i c t y p e , t h i s a l s o k n o w n a s t y p e c a s t i n g . e . g .( f l o a t ) ( x + y / 2 )

Q. What is coercion? How it is implemented?

A n s : I m p l i c i t t y p e c o n v e r s i o n o f a n e x p r e s s i o n i st e r m e d a s c o e r c i o n . A i m p l i c i t t y p e c o n v e r s i o n i s

a c o n v e r s i o n p e r f o r m e d b y t h e c o m p i l e r . T h e J a v ac o m p i l e r c o n v e r t s a l l o p e r a n d s u p t o t h e t y p e o f

t h e l a r g e s t o p e r a n d . T h i s i s d e f a u l t t y p e c o n v e r s i o n .

Q. What do you mean by type casting? What is the type cast operator? [2007]A n s : T h e e x p l i c i t c o n v e r s i o n o f a n o p e r a n d t o a

s p e c i f i c t y p e i s c a l l e d t y p e c a s t i n g . T h e o p e r a t o r

t h a t c o n v e r t s i t s o p e r a n d t o a s p e c i f i e d t y p e i sc a l l e d t h e t y p e c a s t o p e r a t o r . T h e t y p e c a s t o p e r a t o r

i s ( ) i n J a v a a n d i s u s e d a s ( t y p e - t o - b e - c o n v e r t e d -

i n )Q. Explain the methods print() and println()?

A n s : A c o m p u t e r p r o g r a m i s w r i t t e n t o m a n i p u l a t e a

g i v e n s e t o f d a t a a n d t o d i s p l a y o r p r i n t t h er e s u l t s . J a v a s u p p o r t s t w o o u t p u t m e t h o d s t h a t c a n

b e u s e d t o s e n d t h e r e s u l t s t o t h e s c r e e n . p r i n t ( )m e t h o d p r i n t l n ( ) m e t h o d . T h e p r i n t ( ) m e t h o d s e n d s

i n f o r m a t i o n i n t o a b u f f e r . T h i s b u f f e r i s n o t

f l u s h e d u n t i l a n e w l i n e ( o r e n d - o f - l i n e ) c h a r a c t e r

i s s e n t . A s a r e s u l t p r i n t ( ) m e t h o d p r i n t s o u t p u t o n

o n e l i n e . T h e p r i n t l n ( ) m e t h o d b y c o n t r a s t t a k e s t h ei n f o r m a t i o n p r o v i d e d a n d d i s p l a y s i t o n a l i n e

f o l l o w e d b y a l i n e f e e d .Q. What is an Expression? Explain its different types.

I C S E B l u e J




16/53


o f

2 4 8

/ 2 0

/ 2 01 11 1 :

2 7

P M

A n s : A n E x p r e s s i o n i s a n y s t a t e m e n t w h i c h i s

c o m p o s e d o f o n e o r m o r e o p e r a n d s a n d r e t u r n a

v a l e . I t m a y b e c o m b i n a t i o n o f o p e r a t o r s , v a r i a b l e sa n d c o n s t a n t s . T h e r e a r e t h r e e d i f f e r e n t t y p e s o f

e x p r e s s i o n s . ( 1 ) C o n s t a n t E x p r e s s i o n s : 8 * 1 2 / 2 ( 2 )

I n t e g r a l E x p r e s s i o n s : f o r m e d b y c o n n e c t i n g i n t e g e rc o n s t a n t s x = ( a + b ) / 2 ( 3 ) L o g i c a l E x p r e s s i o n s : a >

b o r a ! = bQ. Mention two different styles of expressing a

comment

in a program. [2005]A n s : T h e t w o w a y s o f i n s e r t i n g a c o m m e n t s i n a

p r o g r a m a r e : ( i ) u s i n g / / s i n g l e l i n e c o m m e n t s ( i i )

u s i n g / * * / m u l t i p l e l i n e c o m m e n t sQ. Differentiate between

operator

andexpression

. [2005]

A n s : T h e o p e r a t i o n s a r e r e p r e s e n t e d b y o p e r a t o r sa n d t h e o b j e c t o f t h e o p e r a t i o n s a r e r e f e r r e d t o

a s o p e r a n d s . T h e e x p r e s s i o n i s a n y v a l i dc o m b i n a t i o n o f o p e r a t o r s , c o n s t a n t a n d v a r i a b l e s .

Q. What is a

compound Statement

? Give an Example. [2005]

A n s : I t i s a b l o c k o f c o d e c o n t a i n i n g m o r e t h e no n e e x e c u t a b l e s t a t e m e n t . I n J a v a t h e { } i s c a l l e d

b l o c k a n d t h e s t a t e m e n t s w r i t t e n u n d e r { } i s c a l l e dc o m p o u n d s t a t e m e n t s o r b l o c k s t a t e m e n t . T h e { }

o p e n i n g a n d c l o s i n g b r a c e s i n d i c a t e s t h e s t a r t a n d

e n d o f a c o m p o u n d s t a t e m e n t . f o r ( i n t


17/53

i = 1 ; i < = 5 ; i + + ) {S y s t e m . o u t . p r i n t l n ( " H e l l o " ) ; S y s t e m . o u t . p r in t l n ( " H o w " ) ; S y s t e m . o u t . p r i n t l n ( " a r e y o u ? " ) ; }

U s e o f C o n s t r u c t o r

[ICSE Syllabus on this Topic]Default constructor, Constructor with arguments,

default initializing. Overloading constructor.

Q. What is constructor?A n s : A c o n s t r u c t o r i s a M e m b e r f u n c t i o n t h a ta u t o m a t i c a l l y c a l l e d , w h e n t h e o b j e c t i s c r e a t e d o f

t h a t c l a s s . I t h a s t h e s a m e n a m e a s t h a t o f t h e

c l a s s n a m e a n d i t s p r i m a r y j o b i s t o i n i t i a l i s e t h e

o b j e c t t o a l e g a l v a l u e f o r t h e c l a s s .

Q. Why do we need a constructor as a class member? [2007]

A n s : C o n s t r u c t o r i s u s e d c r e a t e a n i n s t a n c e o f o f ac l a s s , T h i s c a n b e a l s o c a l l e d c r e a t i n g a n o b j e c t .

Q. Why does a constructor should be define as public?

A n s : A c o n s t r u c t o r s h o u l d b e d e f i n e i n p u b l i cs e c t i o n o f a c l a s s , s o t h a t i t s o b j e c t s c a n b e

c r e a t e d i n a n y f u n c t i o n .Q. Explain default constructor? [2006]

A n s : T h e c o n s t r u c t o r t h a t a c c e p t s n o p a r a m e t e r i s

c a l l e d t h e d e f a u l t c o n s t r u c t o r . I f w e d o n o te x p l i c i t l y d e f i n e a c o n s t r u c t o r f o r a c l a s s . , t h e n

j a v a c r e a t e s a d e f a u l t c o n s t r u c t o r f o r t h e c l a s s .

T h e d e f a u l t c o n s t r u c t o r i s o f t e n s u f f i c i e n t f o rs i m p l e c l a s s b u t n o t f o r s o p h i s t i c a t e d

c l a s s e s . E x a m p l e : c l a s s a n t {i n t i ; p u b l i c s t a t i c v o i d

m a i n ( ) a n t n c = n e w a n t ( ) ; }t h e l i n e n e w a n t ( ) c r e a t e sa n o b j e c t a n d c a l l s t h e d e f a u l t c o n s t r u c t o r ,

w i t h o u t i t w e h a v e n o m e t h o d t o c a l l t o b u i l d o u r

o b j e c t s . o n c e y o u c r e a t e a c o n s t r u c t o r w i t ha r g u m e n t t h e d e f a u l t c o n s t r u c t o r b e c o m e s h i d d e n .

Q. Explain the Parameterised constructor?I C S E B l u e J




e / j t h e o r y . h t m 8o f

2 4 8/ 2 0

/ 2 0

1 1

1 1 :


18/53

2 7P M

A n s : I f w e w a n t t o i n i t i a l i s e o b j e c t s w i t h o u r

d e s i r e d v a l u e , w e c a n u s e p a r a m e t e r s w i t h

c o n s t r u c t o r a n d i n i t i a l i s e t h e d a t a m e m b e r s b a s e d

o n t h e a r g u m e n t s p a s s e d t o i t . C o n s t r u c t o r t h a tc a n t a k e a r g u m e n t s a r e c a l l e d P a r a m e t e r i s e dc o n s t r u c t o r . E x a m p l e : p u b l i c c l a s s r e s u l t {i n t p e r ; i n t

t o t ; p u b l i c r e s u l t ( i n t

p e r c e n t a g e ) {p e r = p e r c e n t a g e ; t o t = 0 ; }}

Q. Give an syntax/example of constructor overloading. Define a class, which accept roll

number and marks of a student.Write constructor for the class, which accepts

parameter to initialise the data member. Also take care of the case wherethe studenthas not appeared for the test where just the roll number is passed as argument.

A n s : c l a s s s t u d e n t {i n t r o l l ; f l o a t m a r k s ; s t u d e n t ( i n t r ,

f l o a t m ) / / c o n s t r u c t o r w i t h t w oa r g u m e n t . {r o l l = r ; m a r k s = m ; }s t u d e n t ( i n t r ) / /

c o n s t r u c t o r w i t h o n ea r g u m e n t {r o l l = r ; m a r k s = 0 ; }s t u d e n t ( ) / / d e f a u l t

c o n s t r u c t o r {r o l l = 0 ; m a r k s = 0 ; }}

Q. Mention some characteristics of constructors.A n s : T h e s p e c i a l c h a r a c t e r i s t i c s o f c o n s t r u c t o r s

a r e : ( i ) C o n s t r u c t o r s s h o u l d b e d e c l a r e d i n t h e

p u b l i c s e c t i o n o f t h e c l a s s . ( i i ) T h e y a r e i n v o k e da u t o m a t i c a l l y w h e n a n o b j e c t o f t h e c l a s s i s

c r e a t e d . ( i i i ) T h e y d o n o t h a v e a n y r e t u r n t y p e a n d

c a n n o t r e t u r n a n y v a l u e s . ( i v ) L i k e a n y o t h e rf u n c t i o n , t h e y c a n a c c e p t a r g u m e n t s . ( v ) A c l a s s

c a n h a v e m o r e t h a n o n e c o n s t r u c t o r . ( v i ) D e f a u l t

c o n s t r u c t o r d o n o t a c c e p t p a r a m e t e r s . ( v i i ) I f n oc o n s t r u c t o r i s p r e s e n t i n t h e c l a s s t h e c o m p i l e r

p r o v i d e s a d e f a u l t c o n s t r u c t o r .Q. State the difference between

Constructor

and

Method

. [2005]A n s : T h e f u n c t i o n h a s a r e t u r n t y p e l i k e i n t . b u t

t h e c o n s t r u c t o r h a s n o r e t u r n t y p e . T h e f u n c t i o nm u s t b e c a l l e d i n p r o g r a m s w h e r e a s c o n s t r u c t o r

a u t o m a t i c a l l y c a l l e d w h e n t h e o b j e c t o f t h a t c l a s s

i s c r e a t e d .


19/53

Q. Enter any two variables through constructor parameters and write a program toswap and print the values. [2005]

c l a s s s w a p {i n t a , b ; s w a p ( i n t x , i n t y ) {a = x ; b = y ; }p u b l i c

v o i d m a i n ( S t r i n g a r g s [ ] ) {i n t

t = a ; a = b ; b = t ; S y s t e m . o u t . o u t . p r i n t l n ( " t h e v a l u e o f a

a n d b a f t e r s w a p i n g : " + a + " " + b ) ;I C S E B l u e JT h e o r y h t t p : / / w w w . a m




o f

2 4 8/ 2 0

/ 2 0

1 11 1 :

2 7P M

}}

Q. What are the types of Constructors used in a class?A n s : T h e d i f f e r e n t t y p e s o f c o n s t r u c t o r s a r e a s

f o l l o w s : i . D e f a u l t C o n s t r u c t o r s . i i . P a r a m e t e r i z e d

C o n s t r u c t o r . i i i . C o p y C o n s t r u c t o r s .Q. Define Copy constructors.

A n s : A c o p y c o n s t r u c t o r s i n i t i a l i z e s t h e i n s t a n t

v a r i a b l e s o f a n o b j e c t b y c o p y i n g t h e i n i t i a l v a l u eo f t h e i n s t a n t v a r i a b l e s f r o m a n o t h e r o b j e c t s .

e . g . c l a s s x y z {i n t a . b ; x y z ( i n t x , i n t z ) {a = x ; b = y ; }x y z ( x y z

p ) {a = p . x ; b = p . y ; }}U s e r D e f i n e F u n c t i o n s

[ICSE Syllabus on this Topic]Function as a way to defineoperations/methods/messages. Pure functions return values and do not

changestate, impure functions may return values but also change state,

return type argument to function, functionprototype and function signature,

overloading. Variable of a class type as reference to an objects,invocation

of function on objects through the reference, the concept of this. Argumentpassing in functions,pass by value, what happened when a reference is

passed side effect.Q. What is Function? Why do we use functions while programs handling?

A n s : A n a m e d u n i t o f a g r o u p o f p r o g r a m s

s t a t e m e n t s . T h i s u n i t c a n b e i n v o k e d f r o m o t h e r

p a r t s o f t h e p r o g r a m .


20/53

Q. Define Function prototype?A n s : T h e f u n c t i o n p r o t o t y p e i s t h e f i r s t l i n e o f t h e

f u n c t i o n d e f i n i t i o n t h a t t e l l s t h e p r o g r a m a b o u t t h e

t y p e o f t h e v a l u e r e t u r n e d b y t h e f u n c t i o n a n d t h e

n u m b e r a n d t y p e s o f a r g u m e n t s .

Q. What is the use of void before function name? [2007]A n s : v o i d d a t a t y p e s p e c i f i e s a n e m p t y s e t o f v a l u e s a n d i t i s u s e d a s t h e r e t u r n t y p e f o r

f u n c t i o n s t h a t d o n o t r e t u r n a v a l u e . T h u s a

f u n c t i o n t h a t d o e s n o t r e t u r n a v a l u e i s d e c l a r e d

a s f o l l o w s . v o i d < f u n c t i o n s n a m e > ( p a r a m e t e r l i s t )

Q. Explain Functions/Methods Definitions with syntax?

A n s : A f u n c t i o n m u s t b e d e f i n e d b e f o r e i t i s u s e da n y w h e r e i n t h e p r o g r a m . [ a c c e s s

s p e c i f i e r ] [ m o d i f i e r ] r e t u r n - t y p e f u n c t i o n - n a m e

( p a r a m e t e r l i s t ) {b o d y o f t h e f u n c t i o n }[ a c c e s ss p e c i f i e r ] c a n b e e i t h e r P u b l i c , P r o t e c t e d o r

P r i v a t e . [ m o d i f i e r ] c a n b e o n e o f f i n a l ,n a t i v e , s y n c h r o n i z e , t r a n s i e n t , v o l a t i l e . r e t u r n - t y p e

s p e c i f i e s t h e t y p e o f v a l u e t h a t t h e r e t u r n

s t a t e m e n t o f t h e f u n c t i o n r e t u r n s . I t m a y b e a n yv a l i d J a v a d a t a t y p e . p a r a m e t e r l i s t i s c o m m a

s e p a r a t e d l i s t o f v a r i a b l e s o f a f u n c t i o n .




0

o f2 4 8

/ 2 0/ 2 0

1 1

1 1 :

2 7

P MQ. Why main() function so special?

A n s : T h e m a i n ( ) f u n c t i o n i s i n v o k e d i n t h e s y s t e mb y d e f a u l t . h e n c e a s s o o n a s t h e c o m m a n d f o r

e x e c u t i o n o f t h e p r o g r a m i s u s e d , c o n t r o l d i r e c t l y

r e a c h e s t h e m a i n ( ) f u n c t i o n .

Q. Explain the function prototype and the signature?


21/53

A n s : T h e f u n c t i o n p r o t o t y p e i s t h e f i r s t l i n e o f t h ef u n c t i o n d e f i n i t i o n s , t h a t t e l l s t h e p r o g r a m a b o u t

t h e t y p e o f t h e v a l u e r e t u r n e d b y t h e f u n c t i o n a n d

t h e n u m b e r a n d t y p e o f t h e a r g u m e n t s . F u n c t i o n

s i g n a t u r e b a s i c a l l y r e f e r s t o t h e n u m b e r a n d t y p e s

o f t h e a r g u m e n t s , i t i s t h e p a r t o f t h e p r o t o t y p e .Q. Explain the function of a return statement? [2006]A n s : T h e r e t u r n s t a t e m e n t i s u s e f u l i n t w o w a y s .

F i r s t a n i m m e d i a t e l y e x i t f r o m t h e f u n c t i o n i s

c a u s e d a s s o o n a s a r e t u r n s t a t e m e n t i s

e n c o u n t e r e d a n d t h e c o n t r o l b a c k t o t h e m a i n

c a l l e r . S e c o n d u s e o f r e t u r n s t a t e m e n t i s t h a t i t i s

u s e d a v a l u e t o t h e c a l l i n g c o d e .Q. Write advantages of using functions in programs

A n s : ( i ) f u n c t i o n s l e s s e n t h e c o m p l e x i t y o f

p r o g r a m s ( i i ) f u n c t i o n s h i d e t h e i m p l e m e n t a t i o nd e t a i l s ( i i i ) f u n c t i o n s e n h a n c e r e u s a b i l i t y o f c o d e

Q. Difference between Actual argument and Formal argument? [2007,2008]A n s : T h e p a r a m e t e r t h a t a p p e a r s i n f u n c t i o n c a l l

s t a t e m e n t a r e c a l l e d a c t u a l a r g u m e n t a n d T h e

p a r a m e t e r t h a t a p p e a r s i n f u n c t i o n d e f i n i t i o n a r ec a l l e d f o r m a l p a r a m e t e r .

Q. What are static members?

A n s : T h e m e m b e r s t h a t a r e d e c l a r e d s t a t i c i s c a l l e ds t a t i c m e m b e r s . T h e s e m e m b e r s a r e a s s o c i a t e d

w i t h t h e c l a s s i t s e l f r a t h e r t h e n i n d i v i d u a l o b j e c t s ,

t h e s t a t i c m e m b e r s a n d s t a t i c m e t h o d s a r e o f t e nr e f e r r e d t o a s c l a s s v a r i a b l e s a n d m e t h o d s .

Q. What is the use of static in main() methods? [2007]

A n s : ( i ) T h e y c a n o n l y c a l l o t h e r s t a t i c m e t h o d s .( i i ) T h e y c a n o n l y a c c e s s s t a t i c d a t a . ( i i i ) T h e y

c a n n o t r e f e r t o t h i s o r s u p e r i n a n y w a y .Q. What is

call by value

? [2005]

A n s : ( i ) I n c a l l b y v a l u e , t h e c a l l e d f u n c t i o n s

c r e a t e s i t s o w n w o r k c o p y f o r t h e p a s s e dp a r a m e t e r s a n d c o p i e s t h e p a s s e d v a l u e s i n i t . A n y

c h a n g e s t h a t t a k e p l a c e r e m a i n i n t h e w o r k c o p ya n d t h e o r i g i n a l d a t a r e m a i n s i n t a c t .

Q. Explain the term "passed by reference"? [2007]

A n s : I n p a s s e d b y r e f e r e n c e , t h e c a l l e d f u n c t i o n

r e c e i v e s t h e r e f e r e n c e t o t h e p a s s e d p a r a m e t e r s


22/53

a n d t h r o u g h t h i s r e f e r e n c e , i t a c c e s s t h e o r i g i n a ld a t a . A n y c h a n g e s t h a t t a k e p l a c e a r e r e f l e c t e d i n

t h e o r i g i n a l d a t a .

Q. Differentiate between call by value and call by reference?

A n s : I n c a l l b y v a l u e , t h e c a l l e d f u n c t i o n s c r e a t e s

i t s o w n w o r k c o p y f o r t h e p a s s e d p a r a m e t e r s a n dc o p i e s t h e p a s s e d v a l u e s i n i t . A n y c h a n g e s t h a tt a k e p l a c e r e m a i n i n t h e w o r k c o p y a n d t h e

o r i g i n a l d a t a r e m a i n s i n t a c t . I n c a l l b y r e f e r e n c e ,

t h e c a l l e d f u n c t i o n r e c e i v e s t h e r e f e r e n c e t o t h e

p a s s e d p a r a m e t e r s a n d t h r o u g h t h i s r e f e r e n c e , i t

a c c e s s t h e o r i g i n a l d a t a . A n y c h a n g e s t h a t t a k e

p l a c e a r e r e f l e c t e d i n t h e o r i g i n a l d a t a .Q. Define an impure functions? [2006]

A n s : I m p u r e F u n c t i o n c h a n g e t h e s t a t e o f t h e

o b j e c t a r g u m e n t s t h e y h a v e r e c e i v e d a n d t h e nr e t u r n . T h e f o l l o w i n g f u n c t i o n s i s t h e e x a m p l e o f a n

i m p u r e f u n c t i o n : p u b l i c s t a t i c v o i d i n c r e m e n t ( T i m eo b j , d o u b l e s e c s ) {t i m e . s e c o n d s + = s e c s ; r e t u r n ( T i m e ) ; }

Q. What is the difference between pure and impure functions? [2009]

A n s : P u r e F u n c t i o n : T h e s e f u n c t i o n s t a k e s o b j e c t sa s a n a r g u m e n t s b u t d o e s n o t m o d i f y t h e s t a t e o f

t h e o b j e c t s . T h e r e s u l t o f t h e p u r e f u n c t i o n i s t h e

r e t u r n v a l u e . I m p u r e F u n c t i o n : T h e s e f u n c t i o n sc h a n g e t h e s t a t e o f t h e o b j e c t a r g u m e n t s t h e y h a v e

r e c e i v e d .

Q. How are following passed in Java? [2005](i) primitive types (ii) reference typesA n s : ( i ) B y v a l u e , ( i i ) B y r e f e r e n c e .

I C S E B l u e J



1

o f

2 4 8

/ 2 0/ 2 0

1 11 1 :

2 7

P M

Q. What does function overloading mean? What is its significance?


23/53

A n s : A F u n c t i o n n a m e h a v i n g s e v e r a l d e f i n i t i o n s i nt h e s a m e s c o p e t h a t a r e d i f f e r e n t i a b l e b y t h e

n u m b e r o r t y p e o f t h e i r a r g u m e n t s , i s s a i d t o b e a n

o v e r l o a d e d f u n c t i o n . F u n c t i o n o v e r l o a d i n g n o t o n l y

i m p l e m e n t s p o l y m o r p h i s m b u t a l s o r e d u c e t h e n u m b e r

o f c o m p a r i s o n s i n a p r o g r a m a n d t h e r e b y m a k e st h e p r o g r a m s r u n f a s t e r .Q. Illustrate the concept of function overloading with the help of an example. [2006]

A n s : - A f u n c t i o n n a m e h a v i n g s e v e r a l d e f i n i t i o n s

t h a t a r e d i f f e r e n t i a b l e b y t h e n u m b e r s o r t y p e s o f

t h e i r a r g u m e n t s i s k n o w n a s f u n c t i o n o v e r l o a d i n g .

F o r e x a m p l e f o l l o w i n g c o d e o v e r l o a d s a f u n c t i o n

a r e a t o c o m p u t e r a r e a s o f c i r c l e r e c t a n g l e a n dt r i a n g l e . f l o a t a r e a ( f l o a t r a d i u s ) / / c i r c l e {r e t u r n

( 3 . 1 4 * r a d i u s * r a d i u s ) ; }f l o a t a r e a ( f l o a t l e n g t h ,

f l o a t b r e a d t h ) / / r e c t a n g l e {r e t u r n( l e n g t h * b r e a d t h ) ; }f l o a t a r e a ( f l o a t s i d e 1 , f l o a t

s i d e 2 , f l o a t s i d e 3 ) / / a r e a o f t r i a n g l e {f l o a t s =( s i d e 1 + s i d e 2 + s i d e 3 ) / 2 ; f l o a t a r = M a t h . s q r t ( s

* ( s - s i d e 1 ) * ( s - s i d e 2 ) * ( s - s i d e 3 ) ) ; r e t u r n ( a r ) ; }

Q. What is this keyword? What is its significance? [2009]A n s : T h e t h i s k e y w o r d i s u s e d t o r e f e r t o c u r r e n t l y

c a l l i n g o b j e c t s . T h e m e m b e r f u n c t i o n s o f e v e r y

o b j e c t s h a v e a c c e s s t o a s o r t o f m a g i c k e y w o r dn a m e t h i s , w h i c h p o i n t s t o t h e o b j e c t i t s e l f . T h u s

a n y m e m b e r f u n c t i o n c a n f i n d o u t t h e a d d r e s s o f

t h e o b j e c t o f w h i c h i t i s a m e m b e r . T h e t h i sk e y w o r d r e p r e s e n t s a n o b j e c t t h a t i n v o k e s a m e m b e r

f u n c t i o n . i t s t o r e s t h e a d d r e s s o f t h e o b j e c t t h a t

i n v o k i n g a m e m b e r f u n c t i o n a n d i t i s a n i m p l i c i ta r g u m e n t t o t h e m e m b e r f u n c t i o n b e i n g i n v o k e d .

T h e t h i s k e y w o r d i s u s e f u l i n r e t u r n i n g t h e o b j e c t o f w h i c h t h e f u n c t i o n i s a m e m b e r .

Q. What do you mean by recursive function?

A n s : W h e n a m e t h o d i s c a l l e d i n s i d e i t s o w n

d e f i n i t i o n t h e p r o c e s s i s k n o w n a s f u n c t i o n s

r e c u r s i o n a n d t h i s f u n c t i o n c a l l e d r e c u r s i v ef u n c t i o n .

Q. What is the difference between Methods and Functions?A n s : T h e m a j o r d i f f e r e n c e b e t w e e n m e t h o d s a n d

f u n c t i o n s i s t h a t m e t h o d s c a l l e d b y t h e

r e f e r e n c e v a r i a b l e s c a l l e d o b j e c t s w h e r e a s t h e

f u n c t i o n s d o n o t h a v i n g a n y r e f e r e n c e v a r i a b l e s .


24/53

C l a s s a s a U s e r D e f i n e d T y p e s[ICSE Syllabus on this Topic]Class as a composite type, distinction between

primitive type and composite of class type.

Q. What is data type?

A n s : D a t a t y p e s a r e m e a n s t o i d e n t i f y t h e t y p e o f

d a t a a n d a s s o c i a t e d o p e r a t i o n s o f h a n d l i n g i t .Q. What is composite (user define) data type? Explain with an example? [2007] [2009]A n s : A c o m p o s i t e d a t a t y p e i s t h a t d a t a t y p e t h a t

a r e b a s e d o n f u n d a m e n t a l o r p r i m i t i v e d a t a t y p e s . A

' c l a s s ' i s a n e x a m p l e o f c o m p o s i t e d a t a t y p e s . c l a s s

D a t e {i n t d d , m m , y y ; p u b l i c

D a t e ( ) {d d = 1 ; m m = 1 ; y y = 2 0 0 5 ; }}

Q. What is user define datatype?A n s : A u s e r d e f i n e d d a t a t y p e i s a d a t a t y p e t h a t i s

n o t a p a r t o f t h e l a n g u a g e a n d i s c r e a t e d b y

a p r o g r a m m e r .I C S E B l u e J



e / j t h e o r y . h t m 12

o f

2 4 8/ 2 0

/ 2 0

1 11 1 :

2 7

P MQ. Can you refer to a class as a user defined (composite) datatype? [2009]

A n s : Y e s , w e c a n r e f e r t o a c l a s s n o t h a v i n g am a i n ( ) m e t h o d a s u s e r - d e f i n e d d a t a t y p e .

Q. What is the difference between primitive datatypes and composite datatypes?

A n s : ( i ) p r i m i t i v e d a t a t y p e s a r e b u i l t - i n d a t a t y p e s .

J a v a p r o v i d e s t h e s e d a t a t y p e s . U s e r - d e f i n e d

d a t a t y p e s a r e c r e a t e d b y u s e r s . ( i i ) T h e s i z e o f p r i m i t i v e d a t a t y p e s a r e f i x e d . T h e s i z e o f u s e r -

d e f i n e d d a t a t y p e s a r e v a r i a b l e . ( i i i ) P r i m i t i v ed a t a t y p e s a r e a v a i l a b l e i n a l l p a r t s o f J a v a

p r o g r a m s . T h e a v a i l a b i l i t y o f u s e r - d e f i n e d d a t a t y p e s

d e p e n d s u p o n t h e i r s c o p e .

Q. Compare a class as a user defined datatype and class as an application?


25/53

A n s : I n J a v a , a l l f u n c t i o n a l i t y i s e n c l o s e d i nc l a s s e s . B u t i n o r d e r f o r a c l a s s t o b e u s e r -

d e f i n e d d a t a t y p e , i t s h o u l d b e a c t d i f f e r e n t f r o m

t h a t o f a n a p p l i c a t i o n . i . e . i t s h o u l d n o t i n c l u d e

m a i n ( ) m e t h o d i n i t . A l t h o u g h w e c a n c r e a t e

i n s t a n c e o f c l a s s e s c o n t a i n i n g m a i n m e t h o d , t h e ys h o u l d n o t b e r e f e r r e d t o a s u s e d - d e f i n e d d a t a t y p e .S u c h c l a s s e s ( c o n t a i n i n g m a i n ( ) m e t h o d ) a r e m o r e

a n a l o g u e s t o a p p l i c a t i o n t h a n a d a t a t y p e .

Q. Where can the following members of a class be accessed? private, protected, public

and default access. [2008]

A n s : A c c e s s s p e c i f i e r c a n b e o f f o l l o w i n g t y p e s : ( a )

P U B L I C : P u b l i c m e m b e r s o f a c l a s s a r e g l o b a l l ya c c e s s i b l e . ( b ) P R I V A T E : P r i v a t e m e m b e r s o f a c l a s s

b e a c c e s s e d b y t h e m e m b e r f u n c t i o n s o f t h e c l a s s

o n l y . ( c ) P R O T E C T E D : P r o t e c t e d m e m b e r s o f a c l a s sa r e a c c e s s i b l e i n t h e p a c k a g e w h e r e t h e c l a s s i s

d e f i n e d a n d i n a l l t h e s u b - c l a s s e s o f t h e c l a s s . ( d )D e f a u l t ( f r i e n d l y ) a c c e s s : m e m b e r s w i t h d e f a u l t

( f r i e n d l y ) a c c e s s c a n b e u s e d w i t h i n t h e

p a c k a g e w h e r e t h e c l a s s i s d e f i n e d .Q. How are private member different from public member of a class.

A n s : P r i v a t e m e m b e r s o f a c l a s s a r e a c c e s s i b l e i n

t h e m e m b e r f u n c t i o n o f t h e c l a s s o n l y , w h e r e a sp u b l i c m e m b e r s a r e a c c e s s i b l e g l o b a l l y .

Q. How are protected members different from public and private members of a class.

A n s : P r o t e c t e d m e m b e r s o f a c l a s s a r e a c c e s s i b l ei n a l l t h e c l a s s e s i n t h e s a m e p a c k a g e a n d

s u b c l a s s i n t h e o t h e r p a c k a g e s . p r i v a t e m e m b e r s o f

a c l a s s a c c e s s i b l e i n t h e m e m b e r f u n c t i o n s i n t h ec l a s s o n l y . W h e r e a s p u b l i c m e m b e r s a r e a c c e s s i b l e

g l o b a l l y .Q. Mention any

attributes required for class declaration. [2008]

A n s : T h e t w o a t t r i b u t e s f o r c l a s s d e c l a r a t i o n a r e :

1 . A c c e s s S p e c i f i e r 2 . M o d i f i e r 3 . C l a s s N a m eD e c i s i o n M a k i n g

[ICSE Syllabus on this Topic]Application of if-then, if-then-else, switch(default, break).

Q. What is a statement?

A n s : S t a t e m e n t s a r e t h e i n s t r u c t i o n s g i v e n t t h e

c o m p u t e r t o p e r f o r m a n y k i n d o f a c t i o n , a s


26/53

d a t a m o v e m e n t s , m a k i n g d e c i s i o n o r r e p e a t i n ga c t i o n . S t a t e m e n t s f o r m t h e s m a l l e s t e x e c u t a b l e

u n i t a n d t e r m i n a t e d w i t h s e m i - c o l o n .

Q. What are the three constructs that govern statement flow?

A n s : T h e t h r e e c o n s t r u c t s t h a t g o v e r n s s t a t e m e n t

f l o w a r e : S e q u e n c e , S e l e c t i o n a n d I t e r a t i o nc o n s t r u c t s .Q. What is a selection/conditional statement? Which selection statements does Java

provides?

A n s : A s e l e c t i o n s t a t e m e n t i s t h e o n e t h a t i s u s e d

t o d e c i d e w h i c h s t a t e m e n t s h o u l d b e e x e c u t e n e x t .

T h i s d e c i s i o n i s b a s e d u p o n a t e s t c o n d i t i o n . T h e

s e l e c t i o n s t a t e m e n t s p r o v i d e d b y J a v a a r e : i f - e l s ea n d s w i t c h . T h e c o n d i t i o n a l o p e r a t o r ? : c a n a l s o b e

u s e d t o t a k e s i m p l e d e c i s i o n .

Q. What is an 'if' statement? Explain with an example.A n s : t h e ' i f ' s t a t e m e n t h e l p s i n s e l e c t i n g o n e

a l t e r n a t i v e o u t o f t h e t w o . T h e e x e c u t i o n o f ' i f 's t a t e m e n t s t a r t s w i t h t h e e v a l u a t i o n o f c o n d i t i o n .

T h e ' i f ' s t a t e m e n t t h e r e f o r e h e l p s t h e p r o g r a m m e r

t o t e s t f o r t h e c o n d i t i o n . G e n e r a l f o r m o f ' i f 's t a t e m e n t .

NIIT Offers Java Courses. Fast Track Career Programs. Enroll Now!NIIT.com/Java-Training

Online Tests, Exam Resources &More Classes 9-10 Subjects Maths&ScienceTopperlearning.com/IC

Download NeuroSolutions and apply neural networks to your applicationwww.neurosolutions.com





3o f

2 4 8/ 2 0

/ 2 0

1 1

1 1 :


27/53

2 7P M

i f ( e x p r e s s i o n )

s t a t e m e n t i f ( m a r k s > = 8 0 ) S y s t e m . o u t . p r i n t l n ( " G r a d e A " ) ;

Q. What is the significance of a test-condition in a if statement?

A n s : I t i s t h e t e s t c o n d i t i o n o f a n i f s t a t e m e n tt h a t d e c i d e s w h e t h e r t h e c o d e a s s o c i a t e d w i t h t h ei f p a r t o r t h e o n e a s s o c i a t e d w i t h t h e e l s e p a r t

s h o u l d b e e x e c u t e d . T h e f o r m e r i s e x e c u t e d i f t h e

t e s t c o n d i t i o n e v a l u a t e s t o t r u e a n d t h e l a t t e r

w o r k s i f t h e c o n d i t i o n e v a l u a t e s t o f a l s e .

Q. Write one advantage and one disadvantage of using ?: in place of an if.

A n s : A d v a n t a g e : I t l e a d s t o a m o r e c o m p a c tp r o g r a m . D i s a d v a n t a g e : N e s t e d ? : b e c o m e s d i f f i c u l t

t o u n d e r s t a n d o r m a n a g e .

Q. What do you understand by nested 'if' statements?ORQ. Explain with an examplethe if-else-if construct. [2007]

A n s : A n e s t e d ' i f ' i s a n s t a t e m e n t t h a t h a s a n o t h e r' i f ' i n i t s b o d y o r i n i t ' s a p p e a r a n c e . I t t a k e s

t h e f o l l o w i n g g e n e r a l

f o r m . i f ( c h > = ' A ' ) {i f ( c h < = ' Z ' ) + + u p c a s e ; e l s e + + o t h e r ; }Q. What is the problem of dangling-else? When does it arise? What is the default

dangling-else matching and how it beoverridden?

A n s : T h e n e s t e d i f - e l s e s t a t e m e n t i n t r o d u c e s as o u r c e o f p o t e n t i a l a m b i g u i t y r e f e r r e d t o a s

d a n g l i n g - e l s e p r o b l e m . T h i s p r o b l e m a r i s e s w h e n i n a

n e s t e d i f s t a t e m e n t , n u m b e r o f i f ' s i s m o r e t h e nt h e n u m b e r o f e l s e c l a u s e . T h e q u e s t i o n t h e n a r i s e s ,

w i t h w h i c h i f d o e s t h e a d d i t i o n a l e l s e c l a u s e

p r o p e r t y m a t c h . F o rE x a m p l e i f ( c h > = ' A ' ) i f ( c h < = ' Z ' ) + + u p c a s e ; e l s e + + o t h e r ; T

h e i n d e n t a t i o n i n t h e a b o v e c o d e f r a g m e n ti n d i c a t e s t h a t p r o g r a m m e r w a n t s t h e e l s e t o b e

w i t h t h e o u t e r i f . H o w e v e r J a v a m a t c h e s a n e l s e

w i t h t h e p r e c e d i n g u n m a t c h e d i f . O n e m e t h o d f o r

o v e r - r i d i n g t h e d e f a u l t d a n g l i n g - e l s e m a t c h i n g i s t o

p l a c e t h e l a s t o c c u r r i n g u n m a t c h e d i f i n ac o m p o u n d s t a t e m e n t , a s i t i s

s h o w n b e l o w . i f ( c h > = ' A ' ) {i f ( c h < = ' Z ' ) + + u p c a s e ; }e l s e + + o th e r ;

Q. Compare and contrast IF with ?:

A n s : ( i ) C o m p a r e t o I F s e q u e n c e , ? : o f f e r m o r e

c o n c i s e , c l e a n a n d c o m p a c t c o d e , b u t i t i s l e s s


28/53

o b v i o u s a s c o m p a r e d t o I F . ( i i ) A n o t h e r d i f f e r e n c e i st h a t t h e c o n d i t i o n a l o p e r a t o r ? : p r o d u c e s a n

e x p r e s s i o n , a n d h e n c e a s i n g l e v a l u e c a n b e

a s s i g n e d , f o r l a r g e r e x p r e s s i o n I f i s m o r e f l e x i b l e .

( i i i ) W h e n ? : o p e r a t o r i s u s e d i n i t s n e s t e d f o r m , i t

b e c o m e s c o m p l e x a n d d i f f i c u l t t o u n d e r s t a n d .Q. What is a switch statement? How is a switch statement executed?A n s : S w i t c h s t a t e m e n t s u c c e s s i v e l y t e s t s t h e v a l u e

o f a n e x p r e s s i o n a g a i n s t a s e t o f i n t e g e r s o r

c h a r a c t e r c o n s t a n t s . W h e n a m a t c h i s f o u n d , t h e

s t a t e m e n t s a s s o c i a t e d w i t h t h e c o n s t a n t s a r e

e x e c u t e d . T h e s y n t a x s w i t c h ( e x p r e s s i o n ) {c a s e

c o n s t a n t s : s t a t e m e n t s ; b r e a k ; c a s e c o n s t a n t s :s t a t e m e n t s ; b r e a k ; }T h e e x p r e s s i o n i s e v a l u a t e d a n d

i t s v a l u e s a r e m a t c h e d a g a i n s t t h e v a l u e o f t h e

c o n s t a n t s s p e c i f i e d i n t h e c a s e s t a t e m e n t s . W h e n am a t c h i s f o u n d , t h e s t a t e m e n t s s e q u e n c e a s s o c i a t e d

w i t h t h a t c a s e i s e x e c u t e d u n t i l t h e b r e a k s t a t e m e n to r t h e e n d o f s w i t c h s t a t e m e n t i s r e a c h e d .

Q. What is the significance of break statement in a switch statement?




4

o f2 4 8

/ 2 0

/ 2 01 1

1 1 :2 7

P M

A n s : I n s w i t c h s t a t e m e n t w h e n a m a t c h i s f o u n d t h e

s t a t e m e n t s e q u e n c e o f t h a t c a s e i s e x e c u t e d u n t i l

a ' b r e a k ' s t a t e m e n t i s f o u n d o r t h e e n d o f s w i t c h i sr e a c h e d , w h e n a ' b r e a k ' s t a t e m e n t i s f o u n d

p r o g r a m e x e c u t i o n j u m p s t o t h e l i n e o f c o d ef o l l o w i n g t h e s w i t c h s t a t e m e n t .

Q. What is a control variable in a switch case?


29/53

A n s : A c o n t r o l v a r i a b l e i n s w i t c h c a s e i s o n e w h i c hg u i d e s t h e c o n t r o l t o j u m p o n a s p e c i f i e d c a s e .

e . g . s w i t c h ( x ) , h e r e ' x ' i s t h e c o n t r o l v a r i a b l e .

Q. What is a "fall through"?

A n s : T h e t e r m " f a l l t h r o u g h " r e f e r s t o t h e w a y t h e

s w i t c h s t a t e m e n t e x e c u t e s i t s v a r i o u s c a s es e c t i o n s . E v e r y s t a t e m e n t t h a t f o l l o w s t h e s e l e c t e dc a s e s e c t i o n w i l l b e e x e c u t e d u n l e s s a b r e a k

s t a t e m e n t i s e n c o u n t e r e d .

Q. What is the effect of absence of break in a switch statement?

A n s : A b s e n c e o f b r e a k s t a t e m e n t i n a s w i t c h

s t a t e m e n t l e a d s t o s i t u a t i o n c a l l e d " f a l l t h r o u g h "

w h e r e o n c e a m a t c h i n g c a s e i s f o u n d t h es u b s e q u e n c e c a s e b l o c k s a r e e x e c u t e d

u n c o n d i t i o n a l l y

Q. Write one limitation and one advantage of switch statement?A n s : A d v a n t a g e : M o r e e f f i c i e n t i n c a s e a v a l u e i s

t o b e t e s t e d a g a i n s t a s e t o f c o n s t a n t s .D i s a d v a n t a g e : s w i t c h c a n t e s t o n l y f o r q u a l i t y , s o

f o r t h e r e s t o f c o m p a r i s o n s o n e n e e d s t o u s e i f -

e l s e .Q. Discuss when does an if statement prove more advantageous then switch statement.

A n s : I n t h e f o l l o w i n g c a s e i f s t a t e m e n t p r o v e s t o

b e m o r e a d v a n t a g e o v e r s w i t c h s t a t e m e n t : ( i ) W h e na r a n g e o f v a l u e s n e e d t o b e t e s t e d f o r . ( i i ) W h e n

r e l a t i o n b e t w e e n m u l t i p l e v a r i a b l e s n e e d s t o b e

t e s t e d . ( i i i ) W h e n m u l t i p l e c o n d i t i o n s n e e d t o b et e s t e d . ( i v ) W h e n e x p r e s s i o n s h a v i n g a d a t a t y p e

o t h e r t h e n i n t e g e r o r c h a r a c t e r n e e d t o b e t e s t e d .

Q. When does switch statement prove more advantageous over an if statement?A n s : T h e s w i t c h s t a t e m e n t i s m o r e a d v a n t a g e o u s

t h e n t h e i f s t a t e m e n t w h e n t h e t e s t e x p r e s s i o nw h o s e d a t a t y p e i s e i t h e r o f b y t e , s h o r t , c h a r a c t e r ,

i n t e g e r o r l o n g i s t o b e t e s t e d a g a i n s t a s e t o f

c o n s t a n t s . T h e r e a s o n b e i n g t h a t t h e s w i t c h

s t a t e m e n t e v a l u a t e s t h e e x p r e s s i o n o n c e w h e r e a s

t h e e q u i v a l e n t i f s t a t e m e n t e v a l u a t e s t h e e x p r e s s i o nr e p e a t e d l y .

Q. Explain, with the help of an example, the purpose ofdefault

in a switch statement. [2005]

A n s : T h e d e f a u l t s e c t i o n i s a n o p t i o n a l p a r t o f t h e

s w i t c h s t a t e m e n t a n d t h e s t a t e m e n t w r i t t e n


30/53

u n d e r d e f a u l t c l a u s e a r e e x e c u t e d w h e n n om a t c h i n g c a s e i s f o u n d . s w i t c h ( n ) {c a s e 1 :

S y s t e m . o u t . p r i n t l n ( " S u n d a y " ) ; b r e a k ; c a s e 2 :

S y s t e m . o u t . p r i n t l n ( " M o n d a y " ) ; b r e a k ; c a s e 3 :

S y s t e m . o u t . p r i n t l n ( " T u e s d a y " ) ; b r e a k ; c a s e 4 :

S y s t e m . o u t . p r i n t l n ( " W e d n e s d a y " ) ; b r e a k ; c a s e 5 :S y s t e m . o u t . p r i n t l n ( " T h u r s d a y " ) ; b r e a k ; c a s e 6 :S y s t e m . o u t . p r i n t l n ( " F r i d a y " ) ; b r e a k ; c a s e 7 :

S y s t e m . o u t . p r i n t l n ( " S a t u r d a y " ) ; b r e a k ; d e f a u l t :

S y s t e m . o u t . p r i n t l n ( " I n v a l i d I n p u t " ) ; }

Q. Differentiate between if and switch statements. [2006]

A n s : B o t h a r e u s e d a s a s e l e c t i o n s t a t e m e n t s ,

t h e r e a r e s o m e d i f f e r e n c e i n t h e i r o p e r a t i o n s . ( i )s w i t c h c a n o n l y t e s t f o r e q u a l i t y , w h e r e a s i f c a n

e v a l u a t e a r e l a t i o n a l o r l o g i c a l e x p r e s s i o n . ( i i ) i t

s t a t e m e n t c a n h a n d l e r a n g e s , w h e r e a s s w i t c h c a s el e v e l m u s t b e a s i n g l e v a l u e . ( i i i ) i f s t a t e m e n t c a n

h a n d l e f l o a t i n g p o i n t t e s t a l s o , w h e r e a s t h e s w i t c hc a s e l a b e l s m u s t b e a n i n t e g e r o r c h a r a c t e r .

C o n c e p t s o f C o n d i t i o n s a n d L o o p s

[ICSE Syllabus on this Topic]Utilization of loops. Fixed number of Iteration.The for Loop, unknown number of Iteration - while, do-whileloop, continue,

break. Nested Loops.

Q. What are iteration statements? Name the iteration statements provided by Java?A n s : I t e r a t i o n s t a t e m e n t s a r e s t a t e m e n t s t h a t

a l l o w s a s e t o f i n s t r u c t i o n s t o b e e x e c u t e d

r e p e a t e d l y t i l l s o m e c o n d i t i o n i s s a t i s f i e d . T h ei t e r a t i o n s t a t e m e n t s p r o v i d e d b y J a v a a r e : f o r

l o o p , w h i l e l o o p , d o - w h i l e l o o p .


i t a b h s i r k i c l a s s e s . or g . i n / m a t e r i a l s / i c s


5

o f

2 4 8/ 2 0

/ 2 01 1

1 1 :

2 7

P M


31/53

Q. What is the difference between entry controlled and exit controlled loop? orWhat isthe difference between while and do-while loop?

A n s : w h i l e l o o p i s k n o w n a s e n t r y c o n t r o l l e d l o o p

a n d d o - w h i l e l o o p i s k n o w n a s e x i t - c o n t r o l l e d l o o p .

T h e d i f f e r e n c e s b e t w e e n t h e s e t w o l o o p s a r e : ( 1 ) I n

w h i l e l o o p t h e t e s t e x p r e s s i o n i s e v a l u a t e d a tt h e b e g i n n i n g w h e r e a s i n d o - w h i l e l o o p t e s te x p r e s s i o n i s e v a l u a t e d a t t h e b o t t o m , a f t e r t h e

b o d y o f t h e l o o p . ( 2 ) I n w h i l e l o o p i f t h e t e s t

e x p r e s s i o n i s f a l s e l o o p d o e s n o t c o n t i n u e d b u t i n

d o - w h i l e w h a t e v e r t h e t e s t e x p r e s s i o n t h e l o o p

e x e c u t e a t l e a s t o n c e .

Q. Explain the difference betweenbreak

and

continuewith an example. [2005] [2008]

A n s : B o t h s t a t e m e n t s a r e u s e d a s a j u m p e ds t a t e m e n t . B u t t h e r e i s a d i f f e r e n c e b e t w e e n B r e a k

a n d C o n t i n u e s t a t e m e n t . T h e b r e a k s t a t e m e n t

t e r m i n a t e t h e l o o p , b u t t h e c o n t i n u e s t a t e m e n t s k i pt h e r e s t o f t h e l o o p s t a t e m e n t a n d c o n t i n u e d t h e

n e x t i t e r a t i o n o f t h e l o o p . e . g . o f B r e a k S t a t e m e n t i n t

i = 0 ; w h i l e ( i < = 1 0 ) {i + + ; i f ( i = = 5 ) b r e a k ; S y s t e m . o u t . p r i n t l n (i ) ; }e . g . o f C o n t i n u e S t a t e m e n t i n t

i = 0 ; w h i l e ( i < = 1 0 ) {i + + ; i f ( i = = 5 ) c o n t i n u e ; S y s t e m . o u t . p r i n

t l n ( i ) ; }Q. Compare

java theroy ! easy to learn

Documents