lecture3 tha java language

7/29/2019 Lecture3 Tha Java Language

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The JAVA Language


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11/20/08 Control Statements 2

Comments

Single-line // ... Suitable for brief remarks on the function or structure of a

statement or expression.

Multi-line /* ... */ Good for any comment that will cover more than one line

It requires both opening and closing tags.

Javadoc /** ... */ This is a multi-line comment that the JDKs Javadoc utility can

read and turn into HTML documentation.

Javadoc has tags you can use to extend its functionality.


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11/20/08 Control Statements 3

Code Block

A code block is everything between the curlybraces, and includes the expression thatintroduces the curly brace part:

class MyBlock {

...

...

}


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12/02/09 The Java Langauge: Data Types 4

Data Type Data Type

a scheme for using bits to represent values.

Values are not just numbers, but any kind ofdata that a computer can process.

All values in a computer are representedusing one data type or another.


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Objects

Java has manydata types built into it, and you cancreate as many more as you want.

All data in Java falls into one of two categories:primitive data and objects.

There are only eight primitive data types. Any datatype you invent will be a type of object.


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Objects

A primitive data value uses a small, fixed number of bytes. An object is a big block of data. An object may use many

bytes of memory.

An object usually consists of many internal pieces.

The data type of an object is called its class.

Many classes are already defined in the Java DevelopmentKit.

A programmer can create new classes to meet the particularneeds of a program


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Data Type

1.

byte2. short

3. int

4. long

5.

float6. double

7. char

8. boolean

8primitive(fundamental) Data Types Used inJava:


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Integers

includes byte, short, int, and long

for whole-valued signed numbers

Floating-point numbers

includes float and double

represent numbers with fractional precision

Data Type


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Characters

char

represents symbols in a character set, like letters

and numbers.

Boolean

boolean a special type for representing true/false values

Data Type


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Name Width Range

long 64 9,223,372,036,854,775,808 to

9,223,372,036,854,775,807

int 32 2,147,483,648 to 2,147,483,647

short 16 32,768 to 32,767

byte 8 128 to 127

Integers


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Integers

You can type the number just as you wouldon a typewriter. This is called a literal.

The word "literal" means that a value is

explicitly part of the program.

Example:

125

- literally represents the value one hundred twenty five.


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Floating Point

Name Width in Bits Range

double 64 1.7e308 to1.7e+308

float 32 3.4e038 to3.4e+038


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Explicit Floating Point Literals

single-precision float literal

put a lower case 'f' or upper case 'F' at the end:

123.0f -123.5F -198234.234f 0.00000381F

double-precision double literal.

put a lower case 'd' or upper case 'D' at the end, like this:

123.0d -123.5D -198234.234d 0.00000381D

Remember: Without any letter at the end, a floatingpoint literal will automatically be of type double.


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Floating Point

scientific notation the following are all double-precision literals:

1.23E+02 -1.235E+02 3.81E-06

"E" means "times 10 to the power of"

The integer that follows it says what power of tento multiply the rest of the number by.

Another way of regarding the integer that followsthe "E" is that it says in which direction and forhow many places to shift the decimal point.


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Precision of Float

0.333333333333333333

float data type, has 32 bits only

float has 23 bits of precision. (the rest of the bits areused to indicate the sign and size of the number.)

equivalent to only about 7 decimal places.

the number of places of precision for float is thesame no matter what the size of the number


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Precision of Double

data type double uses 64 bits, and has amuch greater range

It also has a much greater precision: about

15 significant decimal digits.

if you write a literal like 2.345 in a Java

program, it will automatically be regarded asa double, even though a float might be goodenough.


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Characters

char in Java is not the same as char in C Java uses Unicode

char is a 16-bit type. The

range of a char is 0 to 65,536 there are no negative chars.

standard set of characters known as ASCII

still ranges from 0 to 127 as always, and theextended 8-bit character set, ISO-Latin-1,ranges from 0 to 255.
http://localhost/var/www/apps/conversion/tmp/scratch_5/Lecture2%20Tha%20Java%20Language.ppthttp://localhost/var/www/apps/conversion/tmp/scratch_5/Lecture2%20Tha%20Java%20Language.ppt


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Character Literals

a character literal is surrounded with anapostrophe on both sides:

'm' 'y' 'A'

control characters are represented withseveral characters inside the apostrophes

'\n' '\t' \n - 16 bit newline character

\t - represents the tabulation character


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Question

Is this considered a char literal?"W"


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Strings

surrounded by double quotes

Hello!

Characters - Strings


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Booleans

a simple type for logical values

TRUE or FALSE; 0 OR 1

returned by relational operators

required by conditional expressions


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Variables and

Assignment Statements


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Variables

a name for a location in main memory whichuses a particular data type to hold a value

basic unit of storage in a Java program

defined by the combination of an identifier, a

type, and an optional initializer


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Variables

payAmount

type: long

Declaring a variable

where a program says that it needs a variable

type identifier[ = value][, identifier[= value] ...] ;


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Names for Variables

Names

Use only the characters 'a' through 'z', 'A' through 'Z', '0'through '9', character '_', and character '$'.

A name can not contain the space character.

Do not start with a digit.

A name can be any length.

Upper and lower case count as different characters.

So SUM and Sum are different names.

A name can not be a reserved word.

A name must not already be in use


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Variables

Which of the following variable declarationsare correct?

1. long good-by ;

2. short shrift = 0;3. double bubble = 0, toil= 9, trouble = 8

4. byte the bullet ;

5. int double;

6. char thisMustBeTooLong ;

7. int 8ball;


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example

class Example1 {

public static void main ( String args [ ] ) {

// declaration of a variable

long payAmount = 123;

System.out.println("The variable contains: "

+ payAmount );}

}

Variables


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Variables

long payAmount = 123; a declaration of a variable

declaration statements is placed between the twobraces of the main method

it requests a 64 bit section of memory namedpayAmount which uses the primitive data typelong

when the program starts running, the variable willinitially have the value 123 stored in it.


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Variables

payAmount type is "long

NOTE:

a variable cannot be used in a program unless it

has been declared a variable can be declared only once


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Variables

Several ways to declare variables:

dataType variableName;

dataType variableName = initialValue ;

dataType variableNameOne, variableNameTwo ;

dataType variableNameOne = initialValueOne,variableNameTwo = initialValueTwo ;


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Examples

int a, b, c; // declares three ints, a, b, and c.

int d = 3,e, f = 5;

// declares three more ints, initializing d and f.

byte z = 22; // initializes z.

double pi = 3.14159; // declares an approximation of pi

char x = 'x'; // the variable x has the value 'x'


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Variables

class Example2 {public static void main ( String args [ ] ) {long hoursWorked = 40;double payRate = 10.0, taxRate = 0.10;

System.out.println("Hours Worked: " +hoursWorked );

System.out.println("pay Amount : " +(hoursWorked * payRate) );

System.out.println("tax Amount : " +(hoursWorked * payRate * taxRate) );

}}


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Variables

* means multiply (hoursWorked * payRate)

multiply the number stored in hoursWorked by thenumber stored in payRate.

+ means to add charactersto the end of thecharacter string So

"Hours Worked: " + hoursWorked the program will print out:

Hours Worked: 40


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Variables

Output:

Hours Worked: 40

pay Amount : 400.0

tax Amount : 40.0


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Assignment Statement

assignment statement changes the valuethat is held in a variable.

syntax:

variableName = expression ;

equal sign = is the assignment operator.

variableNameis the name of a variable that has been

declared previously in the program

expressionis a collection of characters that calls for avalue


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class Example3 {public static void main ( String args [ ]) {

//a declaration without an initial value

long payAmount ;

//an assignment statement

payAmount = 123;

System.out.println("The variable contains: " +payAmount );

}

}


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semantics of a programming language says whatthe program does as it executes

an assignment statement asks for the computer toperform two steps, in order:

1. Evaluate the expression (that is: calculate a value.)

2. Store the value in the variable.

example sum = 32 + 8 ;



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Expressions and

Arithmetic Operators


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arithmetic operator a symbol that asks fordoing some arithmetic

operators of higherprecedence are donefirst


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Operator Meaning Precedence

- unary minus highest

+ unary plus highest

* multiplication middle

/ division middle

% remainder middle

+ addition low

- subtraction low


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Operators

Operator Result

++ Increment

+= Addition assignment-= Subtraction assignment

*= Multiplication assignment

/= Division assignment

%= Modulus assignment

- - Decrement


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Modulus Operator

modulus operator, %, returns the remainderof a division operation

can be applied to floating-point types as well

as integer types.

example:

let x = 42; double y = 42.3;x % 10 = 2

y % 10 = 2.3


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the ? Operator

a special ternary(three-way) operatorthatcan replace certain types ofif elsestatements

general form:expression1 ?expression2: expression3

expression1 can be any expression that evaluatesto a boolean value

ifexpression1 is true, then expression2isevaluated; otherwise, expression3is evaluated


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the ? Operator

example

ratio = denom == 0 ? 0 : num / denom;

ifdenom equals zero, then 0 is assigned to ratio

ifdenom is not equal zero, then num/denom will

be executed


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Relational Operator

Operator Result

== Equal to

!= Not equal to

> Greater than

< Less than

>= Greater than or equal to


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Boolean Logical Operator

Operator Result

& Logical AND| Logical OR

^ Logical XOR (exclusive OR)|| Short-circuit OR&& Short-circuit AND! Logical unary NOT&= AND assignment|= OR assignment

^= XOR assignment== Equal to!= Not equal to?: Ternary if-then-else


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Bitwise Operator

Operator Result~ Bitwise unary NOT& Bitwise AND| Bitwise OR^ Bitwise exclusive OR

>> Shift right>>> Shift right zero fill>= Shift right assignment>>>= Shift right zero fill assignment


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Bitwise Logical Operator

A B A | B A & B A ^ B ~A

0 0 0 0 0 1

1 0 1 0 1 0

0 1 1 0 1 1

1 1 1 1 0 0


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Shift Operators

Operator Use Operation

>> op1 >> op2 shift bits of op1 right bydistance op2

> op1 >>> op2 shift bits of op1 right bydistance op2(unsigned)


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shift operator performs bit manipulation ondata by shifting the bits of its first operandright or left.

the shift occurs in the direction indicated bythe operator itself

Shift Operators


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example1

13 >> 1;

the following statement shifts the bits of theinteger 13 to the right by one position

13 is 1101(in binary)

0110 or 6 in decimal

Shift Operators


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example2

int i = 8; 1000

i >>=2; 0010

answer: i =2

Shift Operators


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Operator PrecedenceHighest

( ) [ ] .++ -- ~ !* / %+ ->> >>> >= <


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Expressions

expression

a combination of literals, operators,variable names, and parentheses used to calculatea value.

literal characters that directly mean a value, like: 3.456 operator a symbol like plus + or times * that asks for an

arithmetic operation

operand a value that is acted upon by an operator

variable a section of memory containing a value. parentheses ()


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Expressions

subexpression a part of an expressionthat is by itself a correct expression

example 13 5

13& 5 operand

operator

5 subexpression

(32 - y) / ( x + 5 )

(32 y) & (x + 5) operand

/operator

/(x+5) subexpression


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Expressions

an expression can be written without usingany spaces

example (hoursWorked*payRate)-deduction

(hoursWorked * payRate) - deduction

The following is NOT correct: ( hours Worked * pay Rate) -deduction


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Expressions

1. -153

2. (12 - 33. x + p

4. *z 99

5. -sum / -value

6. 2 - value

7. ((m - n) + (w*x+z) / (p % q )

8. (a-b) * (c-d)9. A - b/c + D

10. -sum + partial

11. ( (x+y) / z ) / ( a - b )

12. 2( a - b )

Check if the following expression isCORRECT orNOT


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Exercise

Find the value of the following expressions

1. 16 - 12 / 4 =

2. 2 + 6 / 2 =

3. 8 + 4*2 =

4. 8+4 * 2 =

5. 12/2 3 =

6. 6/8 + 2 = 6/8 is done using integer division, resulting in 0;

then that 0 is added to 2.


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SELF TEST

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