1. Why is Java known as a platform-neutral language?

Ans.

Java is known as platform-neutral language because Java's bytecodes are designed to be read, interpreted, and executed in exactly the same manner on any computer hardware or operating system that supports a Java run-time.

2. How is Java more secure than other languages?

Ans.

One of the potential terrors of the Internet is the possibility of security breaches- viruses that infect your computer, or hackers who take advantage of a software glitch to invade your personal cyberspace and make off with confidential information.

Applets, which are Java programs, are automatically downloaded when a Web page is displayed. Java applets, by default, execute within the Java executing environment and are limited to the environment. This means, an applet cannot access the local file system or other programs of the system where it executes. This reduces the chance that simply viewing someone's page might harm your system or data. No system is absolutely reliable and none will ever be; but Java represents the state-of-the-art in reducing the chances of a disaster. 3. What is multithreading? How does it improve the performance of Java?

Ans.

In a multithreading environment, a thread is the smallest unit of dispatchable code. This means that a single program can perform two or more tasks simultaneously. For instance a text editor can format text at the same time that it is printing.

The benefit of Java's multithreading is that the main loop/polling mechanism is eliminated. One thread can pause without stopping other parts of the program. For example, the idle time created when a thread reads data from a network or waits for user input can be utilized elsewhere. When a thread blocks in a Java program, only the single thread that is

blocked pauses. All other threads continue to run.

2. What is a bytecode ?

Ans:

Bytecode is a compiled format of a Java program. Once a Java program is converted into bytecode it can be transferred across the network and executed by a Java Virtual Machine (JVM).

3. What is an appletviewer?

Ans:

An appletviewer allows you to run an applet without the overhead of running a Web browser.

4. Define Garbage Collection.

Ans:

Garbage Collection is a process that automatically frees the memory of objects that are no longer in use. There is no specification of a technique for garbage collection. The implementation has been left to vendors1.

What is object-oriented programming?

How is it different from the procedure-oriented programming?

Ans.

Object- oriented programming is a method of implementation in which programs are organized as co-operative collection of objects, each of which represents an instance of some class and whose classes all members of a hierarchy of classes united in inheritance relationships.

With procedural programming you are able to combine returning sequences of statements into one single place. A procedure call is used to invoke the procedure. After the sequence is processed, flow of control proceeds right after the position where the call was made

8. Why is the main() method in Java declared static?

Ans.

The keyword static helps to specify that the main() method can be called without instantiating an object of a class. This is necessary because the main() method is called by the Java interpreter before any objects are created.

public static void main (String args[])

{//code}

After specifying the keyword static, you specify the void keyword. This keyword indicates to the compiler that, the main() method does not return a value.

9. What is an applet?

Ans.

Applets are small Java programs developed for Internet applications. An applet located on a distant computer (Server) can be downloaded via Internet and executed on a local computer (Client) using a Java-capable browser.

10. Explain with a simple example how to create, compile and run a program in Java.

Ans.

Java program involves two steps:

1. Compiling source code into bytecode using javac compiler

2. Executing the bytecode program using java interpreter

For example, consider the following program

class ProgramDemo

{

public static void main (String args[])

{

System.out.println("Here is your string");

}

}

First, save the program as ProgramDemo.java. Then, to compile this program type the following command at command prompt:

C:\Dir1> javac ProgramDemo.java.

Once the program compiles successfully run this program by typing the following command at command prompt:

C:\Dir1> java ProgramDemo 5. What is type casting? Why is it required in programming?

Ans.

The process of converting one data type to another is called casting.

Type variable1 = (type) variable2;

Examples:

int m = 50;

byte n = (byte)m;

long distance = (long)m;

Type casting is required in programming when you want to assign the value of one variable to another variable of different data type.

10. Write a program to convert the given temperature in Fahrenheit to Celsius using the following conversion formula

F-32

C = 1.8 and display the values in a tabular form.

Ans.

public class Celsius

{

double celsius;

double fahrenheit;

public Celsius()

{

fahrenheit=98.4;

}

public void convert()

{

celsius=(fahrenheit-32)/1.8;

System.out.println("Temperature in celsius: "+celsius);

}

public static void main(String a[])

{

Celsius object=new Celsius();

object.convert();

}

}

1. Compare in terms of their functions, the following pairs of statements:

(a) while and do........while.

(b) while and for.

(c) break and continue.

Ans.

(a) The difference between the do-while statement and the while statement is that in the while statement, the loop body is executed only when the condition stated in the statement is true. In the do-while loop, the loop body is executed at least once, regardless of the condition evaluating to true or false. The while loop is also called the top tested loop whereas the do-while loop is also called the bottom tested loop.

(b) In the for loop, three sections, initialization, test condition and increment/decrement are placed in the same line whereas in the while loop, all three sections are placed in three different places in a program. In the for

loop, more than one variable can be initialized, tested and incremented at a time.

(c) The continue statement stops the current iteration of a loop and immediately starts the next iteration of the same loop. When the current iteration of a loop stops, the statements after the continue statement in the loop are not executed. The break statement immediately terminates the loop, bypassing the conditional expression and any remaining code in the body of the loop. When a break statement is encountered inside the loop, the loop is terminated and program control resumes the next statement following the loop. 2. Why are arrays easier to use compared to a bunch of related variables?

Ans.

An array is a sequence of logically related data items. It is a kind of row made of boxes, with each box holding a value.

Arrays have following advantages over bunch of related variables:

1 Arrays of any type can be created. They can have one or more dimensions.2 Any specific element can be indexed in an array by its index.

All like type variables in an array can be referred by a common name

2. Distinguish between Multiprocessing and Multithreading.

Ans.

Multiprocessing: Refers to a computer system's ability to support more than one process (program) at the same time. Multiprocessing operating systems enable several programs to run concurrently Multiprocessing systems are much more complicated than single-process systems because the operating system must allocate resources to competing processes in a reasonable manner.

Multithreading : The ability of an operating system to execute different parts of a program, called threads, simultaneously. The programmer must carefully design the program in such a way that all the threads can run at the same time without interfering with each other.

4. What is Synchronization? Why do we use it?

Ans.

Multithreading introduces a synchronous behavior in programs. There is a need to enforce synchronicity when it is necessary. For example, if two threads are to communicate and share a data structure, there is a need to avoid conflict between them. That is, a thread must be prevented from writing data while the other thread is reading the data.

To overcome this problem, Java implements a model of interprocess communication called monitor. The monitor is a control mechanism that can hold only one thread at a time. Once a thread enters a monitor, all other threads have to wait until that exits from the monitor

1. Why is Java known as platform neutral language and how is Java more secured than other languages?

Ans. Java is the first programming language that is not tied to any other particular hardware or operating system. Programs developed in Java can be executed anywhere on any system. We can call Java as a revolutionary technology because it has brought in a fundamental shift in how we develop and use programs. Nothing like this has happened to the software industry before. Thus, Java known as “platform neutral language”.Applets, the Java programs which automatically downloaded when a web page is displayed, are subject to a number of limitations that are designed to reduce the chance that simply viewing someone’s page might result in harm to user’s system or data. No such system is absolutely reliable non will ever be; but Java represents the state-of-the-art in reducing the chances of a disaster. So, Java is more secured than other languages.5.List the eight basic data types used in Java. Give

examples.

The eight basic data types used in java are:

byte: It is the smallest integer type. This is a signed 8-bit type and has a range from -128 to 127. For example, the following declaration declares two variables B and C of type byte.

byte b,c;

b =2;

c = -114;

short: It is a signed 16-bit type and has a range from -32,768 to 32,767. For example, the following declaration declares variable K of type short.

short k;

k = 2;

int: It is a signed 32-bit type and has a range from -2,147,483,648 to 2,147,483,647.

For example,

int x = 10;

int j = 98;

long: This is signed 64-bit type and has a range from -263 to 263 -1.

For example,

long ds = 1000;

long se;

se =ds * 24 * 60 * 60;

double: It uses 64 bits to store a value.

For example,

double P, R;

P = 10.8;

R =3.14215;

float: It uses 32 bits to store a value.

For example,

float x;

x = -1111; int : It uses 32 bits to store a value.

For example,

Int score;

Score=90;

char: this data type is used to store characters. It is 16-bit type and has a range from 0 to 65,536.

For example,

char c1,c2;

c1 =84;

c2 ='g';

boolean: it can have only one of two possible values, true or false.

For example,

boolean flag;

flag= false;

11. What is an array?

Ans.

An array is a sequence of logically related data items. It is a kind of row made of boxes, with each box holding a value. The number associated with each box is the index of the item. Each box can be accessed by, first box, second box, third box, and so on, till the nth box. The first box, or the lowest bound of an array is always zero, which means, the first item in an array is always at position zero of that array. Position in an array is called index. So the third item in an array would be at index 2 (0, 1, 2).

1. Compare in terms of their functions, the following pairs of statements:

(a) while and do........while.

(b) while and for.

(c) break and continue.

Ans.

(a) The difference between the do-while statement and the while statement is that in the while statement, the loop

body is executed only when the condition stated in the statement is true. In the do-while loop, the loop body is

executed at least once, regardless of the condition evaluating to true or false. The while loop is also called the top

tested loop whereas the do-while loop is also called the bottom tested loop.

(b) In the for loop, three sections, initialization, test condition and increment/decrement are placed in the same line

whereas in the while loop, all three sections are placed in three different places in a program. In the for loop,

more than one variable can be initialized, tested and incremented at a time.

(c) The continue statement stops the current iteration of a loop and immediately starts the next iteration of the same

loop. When the current iteration of a loop stops, the statements after the continue statement in the loop are not

executed. The break statement immediately terminates the loop, bypassing the conditional expression and any

remaining code in the body of the loop. When a break statement is encountered inside the loop, the loop is

terminated and program control resumes the next statement following the loop.

3. What are objects? How are they created from a class?

Ans.

An object in java is a block of memory that contains a space to store all the instance variables. As with real-world

objects, software objects have state and behavior. In programming terms the state of an object is determined by its

data (variables); the behavior by its methods. Thus a software object combines data and methods into one unit.

Creating an object is referred to as instantiating an object. The creating object to a class is two-step process:

8) Compare in terms of their functions, the following pairs of statements:

a. while and do……….while

Ans.

Continue Break

a) The continue statement stops the current

iteration of a loop and immediately starts the

next iteration of the same loop.

b) When the current iteration of a loop stops the

statement after the continue statement in the

loop are not executed.

c) You can use the continue statement in the

while, do-while and for statements but not in the

switch statement.

a) We can force immediate termination of

loop, by passing any remaining code in the

body of the loop.

b) Break statement is encountered inside the

loop, the loop is terminated and program

control resumes the next statement.

c) You can use the continue statement in the

while, do-while and for statements and also

use in the switch statement.

While For

i) In this you can’t Initialized more than one variable at

a time.

ii) Like initialization section the increment section also

not have more than two parts.

iii) It is not permissible to use expression

in the initialization and the Increment

parts.

i) You can Initialized more than one

variable at a time.

ii) increment section also not have more

than two parts.

iii) It is permissible to use expression in the

initialization and the Increment parts.

While Do-While

1. The loop body is executed only

when the condition stated in the

statement is true.

2. It is also called top tested loop.

3. Before the loop body executed, the

condition of the while statement

evaluated.

1.The loop body is executed at least

once, regardless of the condition

evaluating to true & false.

2. It is also called bottom tested loop.

3. After the loop body is executed once, the

condition in the do-while statement

checked.