FifthSemester_JAVA_Quesiton Answer

1. Major Features of Java

  • Simple – Easy syntax, no pointers, automatic memory management.
  • Object Oriented – Uses class and object, supports encapsulation, inheritance, polymorphism, abstraction.
  • Platform Independent – “Write Once, Run Anywhere” (Bytecode runs on JVM).
  • Secure – No pointer manipulation, bytecode verification, security manager.
  • Robust – Strong memory management, exception handling.
  • Multithreaded – Supports multiple threads execution.
  • Distributed – Supports RMI, networking API.
  • Portable – Same size of primitive types on all systems.
  • High Performance – Uses JIT compiler.

2. Multithreading

Definition:
Multithreading is the process of executing multiple threads simultaneously within a single program.

Example:

class A extends Thread{

public void run(){System.out.println("Thread running");}

public static void main(String[] args){

A t=new A();

t.start();

}

}

3. Difference Between while and do-while

while

do-while

Entry controlled loop

Exit controlled loop

Condition checked first

Condition checked after execution

May execute 0 times

Executes at least once

 

 

Example:

int i=1;

while(i<=3){System.out.println(i);i++;}

 

int j=1;

do{System.out.println(j);j++;}while(j<=3);

4. Sum of Two Numbers (Using Console)

import java.util.*;

class Sum{

public static void main(String[] a){

Scanner s=new Scanner(System.in);

int x=s.nextInt(),y=s.nextInt();

System.out.println(x+y);

}

}

5. Why Use Interface in Java?

Interface is used to achieve:

  • 100% abstraction
  • Multiple inheritance
  • Loose coupling
  • Standardization

It contains abstract methods (by default public & abstract).

Example:

interface A{void show();}

class B implements A{

public void show(){System.out.println("Hello");}

public static void main(String[] a){new B().show();}

}

 

6. UI Program (Factorial)

import java.awt.*;

import java.awt.event.*;

 

class F extends Frame implements ActionListener{

TextField t1=new TextField(10),t2=new TextField(10);

Button b=new Button("OK");

 

F(){

setLayout(new FlowLayout());

add(new Label("Enter Number"));add(t1);

add(new Label("Factorial"));add(t2);

add(b);

b.addActionListener(this);

setSize(300,200);setVisible(true);

}

 

public void actionPerformed(ActionEvent e){

int n=Integer.parseInt(t1.getText()),f=1;

for(int i=1;i<=n;i++)f*=i;

t2.setText(String.valueOf(f));

}

 

public static void main(String[] a){new F();}

}

 

1. What is JVM? Explain features of Java.

JVM (Java Virtual Machine)

JVM is a virtual machine that executes Java bytecode.
It converts bytecode into machine code and makes Java platform independent.

Main Functions:

  • Loads class files
  • Verifies bytecode
  • Executes program
  • Manages memory (Garbage Collection)

Features of Java:

  • Simple
  • Object Oriented
  • Platform Independent
  • Secure
  • Robust
  • Multithreaded
  • Portable
  • Distributed
  • High Performance (JIT)

2. Constructor & Types

Constructor

A constructor is a special method having same name as class, used to initialize objects.
It has no return type and is called automatically when object is created.

Types:

  1. Default Constructor
  2. Parameterized Constructor

Example:

class A{

A(){System.out.println("Default");}

A(int x){System.out.println("Parameterized "+x);}

public static void main(String[] a){

new A();

new A(10);

}

}

OR

Method Overloading

Method overloading means same method name with different parameters in same class.

Condition:

  • Parameters must differ (number/type)

Example:

class A{

int add(int a,int b){return a+b;}

int add(int a,int b,int c){return a+b+c;}

public static void main(String[] x){

A o=new A();

System.out.println(o.add(2,3));

System.out.println(o.add(2,3,4));

}

}

3. Types of Inheritance

  1. Single
  2. Multilevel
  3. Hierarchical
  4. Multiple (through interface)
  5. Hybrid (using interface)

Multilevel Inheritance Example:

class A{void show(){System.out.println("A");}}

class B extends A{}

class C extends B{

public static void main(String[] a){

new C().show();

}

}

Interface vs Class

Class

Interface

Can have method body

Methods are abstract (default)

Supports single inheritance

Supports multiple inheritance

Can have constructors

No constructor

Can have instance variables

Only constants

 

Method Overriding

When subclass provides specific implementation of parent method.

Condition:

  • Same method name
  • Same parameters

Example:

class A{void show(){System.out.println("Parent");}}

class B extends A{

void show(){System.out.println("Child");}

public static void main(String[] a){

A o=new B();

o.show();

}

}

4. Categories of Exceptions

  1. Checked Exception (Compile-time)
    Example: IOException
  2. Unchecked Exception (Runtime)
    Example: ArithmeticException
  3. Error (Serious problem)
    Example: OutOfMemoryError

throws Keyword

Declares exception.

throw Keyword

Explicitly throws exception.

Example:

class A{

static void m() throws Exception{throw new Exception();}

public static void main(String[] a) throws Exception{

m();

}

}

5. What is Stream?

Stream is a sequence of data used for input and output.

Types:

  1. Byte Stream
    Classes: InputStream, OutputStream
  2. Character Stream
    Classes: Reader, Writer

Character Stream Classes:

  • FileReader
  • FileWriter
  • BufferedReader
  • BufferedWriter

Example:

import java.io.*;

class A{

public static void main(String[] a) throws Exception{

FileWriter f=new FileWriter("a.txt");

f.write("Hello");

f.close();

}

}

6. Component vs Container

Component

GUI element like Button, Label, TextField.

Container

Holds components (Frame, Panel).

Container can add components using add() method.

Event Handling (Action Event)

When user clicks button, event is generated.

Steps:

  1. Implement ActionListener
  2. Register listener
  3. Override actionPerformed()

Example:

import java.awt.*;

import java.awt.event.*;

 

class A extends Frame implements ActionListener{

Button b=new Button("OK");

A(){

add(b);

b.addActionListener(this);

setSize(200,200);

setVisible(true);

}

public void actionPerformed(ActionEvent e){

System.out.println("Clicked");

}

public static void main(String[] a){new A();}

}

 

✅ 1. Byte Code & Java Architecture

Byte Code

Byte code is the intermediate code generated by Java compiler (.class file).
It is platform independent and executed by JVM.

Java Source (.java) → Compiler (javac) → Bytecode (.class) → JVM → Machine Code

Java Architecture

Components:

  1. JDK – Development tools (javac, debugger).
  2. JRE – Runtime environment.
  3. JVM – Executes bytecode.

JVM Internal Parts:

  • Class Loader
  • Method Area
  • Heap
  • Stack
  • Program Counter
  • Execution Engine
  • Garbage Collector

Diagram (Exam Draw Format)

.java → javac → .class → JVM → OS → Hardware

✅ 2. Types of Loops in Java

  1. for loop
  2. while loop
  3. do-while loop

Factorial Program

import java.util.*;

class A{

public static void main(String[] a){

Scanner s=new Scanner(System.in);

int n=s.nextInt(),f=1;

for(int i=1;i<=n;i++)f*=i;

System.out.println(f);

}

}

OR

Static Data Members & Static Methods

Static Data Member

  • Belongs to class, not object
  • Shared by all objects
  • Accessed using class name

Static Method

  • Belongs to class
  • Can access only static members
  • Called without object

Example:

class A{

static int x=10;

static void show(){System.out.println(x);}

public static void main(String[] a){

A.show();

}

}

✅ 3. Interface & Multiple Inheritance

Interface

Interface is a collection of abstract methods.
Used to achieve 100% abstraction and multiple inheritance.

Multiple Inheritance Using Interface

interface A{void show();}

interface B{void display();}

class C implements A,B{

public void show(){System.out.println("A");}

public void display(){System.out.println("B");}

public static void main(String[] a){

C o=new C();

o.show();o.display();

}

}

OR

Importance of Inheritance

  • Code reusability
  • Method overriding
  • Extensibility
  • Reduces duplication

Single Inheritance Example

class A{void show(){System.out.println("Parent");}}

class B extends A{

public static void main(String[] a){

new B().show();

}

}

✅ 4. Exception & try-catch-finally

Exception

An exception is an abnormal condition that disrupts program flow.

Keywords:

  • try → risky code
  • catch → handle exception
  • finally → always executes

Example:

class A{

public static void main(String[] a){

try{

int x=10/0;

}

catch(Exception e){

System.out.println("Error");

}

finally{

System.out.println("Done");

}

}

}

✅ 5. Byte Stream Classes

Byte stream is used for binary data (image, audio).

Superclasses:

  • InputStream
  • OutputStream

Important Classes:

  • FileInputStream
  • FileOutputStream
  • BufferedInputStream
  • BufferedOutputStream

Example:

import java.io.*;

class A{

public static void main(String[] a) throws Exception{

FileOutputStream f=new FileOutputStream("a.txt");

f.write(65);

f.close();

}

}

✅ 6. Event Handling

Event handling is mechanism to handle user actions (click, key press).

Uses:

  • Event Source
  • Event Listener
  • Event Object

Handling Action Event

Steps:

  1. Implement ActionListener
  2. Register listener
  3. Override actionPerformed()

Example:

import java.awt.*;

import java.awt.event.*;

 

class A extends Frame implements ActionListener{

Button b=new Button("OK");

A(){

add(b);

b.addActionListener(this);

setSize(200,200);

setVisible(true);

}

public void actionPerformed(ActionEvent e){

System.out.println("Clicked");

}

public static void main(String[] a){new A();}

}

 

1. What is polymorphism? Write example program to illustrate method overriding.

Polymorphism

Polymorphism means one name, many forms.
In Java, polymorphism allows a method to behave differently in different classes.

Types:

  • Compile-time (Method Overloading)
  • Run-time (Method Overriding)

Method Overriding

When a child class provides its own implementation of a method already defined in parent class.

Example Program

class A {

    void show() {

        System.out.println("Parent class");

    }

}

 

class B extends A {

    void show() {

        System.out.println("Child class");

    }

 

    public static void main(String[] args) {

        A obj = new B();

        obj.show();

    }

}

2. Differentiate between switch and if statement with example program.

Difference between if and switch

if statement

switch statement

Used for conditions

Used for fixed values

Supports logical operators

Does not support logical operators

Slower for many conditions

Faster for multiple choices

Can test ranges

Cannot test ranges

Example (if)

int a = 5;

if(a == 5)

    System.out.println("Five");

Example (switch)

int a = 5;

switch(a) {

    case 5: System.out.println("Five");

}

3. Why throws keyword is used in exception handling? Write program to handle array index out of bound error.

throws Keyword

The throws keyword is used to declare exceptions that a method may pass to the calling method.

Purpose:

  • Delegates exception handling
  • Improves program readability

Example Program

class Test {

    static void show() throws ArrayIndexOutOfBoundsException {

        int a[] = {1, 2};

        System.out.println(a[5]);

    }

 

    public static void main(String[] args) {

        try {

            show();

        } catch(Exception e) {

            System.out.println("Array index error");

        }

    }

}

4. How abstract class is created in Java? Explain why abstract class is used with example.

Abstract Class

An abstract class is a class that cannot be instantiated and may contain abstract methods.

Creation

  • Use abstract keyword
  • Can have abstract and non-abstract methods

Why Abstract Class is Used

  • To achieve abstraction
  • To define common behavior
  • To force child classes to implement methods

Example

abstract class A {

    abstract void show();

}

 

class B extends A {

    void show() {

        System.out.println("Abstract method implemented");

    }

 

    public static void main(String[] args) {

        B obj = new B();

        obj.show();

    }

}

OR

Java program to create database to store 2 book records

import java.sql.*;

 

class BookDB {

    public static void main(String[] args) throws Exception {

        Connection con = DriverManager.getConnection(

            "jdbc:mysql://localhost:3306/test", "root", "");

 

        Statement st = con.createStatement();

        st.execute("create table book(isbn int, title varchar(20), author varchar(20), price int, page int)");

 

        st.execute("insert into book values(1,'Java','James',500,300)");

        st.execute("insert into book values(2,'C','Dennis',400,250)");

 

        System.out.println("Records inserted");

    }

}

(Only write logic part if short on time)

5. Java program to create GUI window with two text fields and two buttons using GridLayout.

import java.awt.*;

 

class GridDemo {

    GridDemo() {

        Frame f = new Frame();

        f.setLayout(new GridLayout(2,2));

 

        f.add(new TextField());

        f.add(new TextField());

        f.add(new Button("OK"));

        f.add(new Button("Cancel"));

 

        f.setSize(200,200);

        f.setVisible(true);

    }

 

    public static void main(String[] args) {

        new GridDemo();

    }

}

OR

What is adapter class? Why adapter class is used? Explain with example.

Adapter Class

Adapter class is a predefined class that provides empty implementation of listener interfaces.

Why Adapter Class is Used

  • Avoid implementing all methods
  • Improves code readability
  • Reduces coding effort

Example

import java.awt.event.*;

 

class MyAdapter extends MouseAdapter {

    public void mouseClicked(MouseEvent e) {

        System.out.println("Mouse clicked");

    }

}

6. Java program to take 2 double data from user and store them in tendouble.txt file.

import java.io.*;

import java.util.*;

 

class FileDemo {

    public static void main(String[] args) throws Exception {

        Scanner sc = new Scanner(System.in);

        double a = sc.nextDouble();

        double b = sc.nextDouble();

 

        FileWriter fw = new FileWriter("tendouble.txt");

        fw.write(a + "\n" + b);

        fw.close();

 

        System.out.println("Data stored");

    }

}

 

1. Define inheritance. Identify different types of inheritance with example.

Inheritance

Inheritance is the process by which one class acquires properties and methods of another class using the extends keyword.

Advantages:
Code reusability, easy maintenance, less redundancy.

Types of Inheritance in Java

  1. Single
  2. Multilevel
  3. Hierarchical
  4. Multiple (using interface)

Example (Single Inheritance)

class A{ void show(){ System.out.println("A"); } }

class B extends A{

 public static void main(String[] a){

  new B().show();

 }

}

2. Create a GUI window to collect name, address, phone, gender, hobbies and submit button.

import java.awt.*;

 

class Form{

 Form(){

  Frame f=new Frame();

  f.setLayout(new GridLayout(6,2));

  f.add(new Label("Name")); f.add(new TextField());

  f.add(new Label("Address")); f.add(new TextField());

  f.add(new Label("Phone")); f.add(new TextField());

  f.add(new Label("Gender")); f.add(new Checkbox("Male"));

  f.add(new Label("Hobby")); f.add(new Checkbox("Reading"));

  f.add(new Button("Submit"));

  f.setSize(300,300); f.setVisible(true);

 }

 public static void main(String[] a){ new Form(); }

}

OR

Java program using GridLayout and FlowLayout

import java.awt.*;

 

class Layout{

 Layout(){

  Frame f1=new Frame();

  f1.setLayout(new FlowLayout());

  f1.add(new Button("A"));

 

  Frame f2=new Frame();

  f2.setLayout(new GridLayout(2,2));

  f2.add(new Button("1")); f2.add(new Button("2"));

  f2.add(new Button("3")); f2.add(new Button("4"));

 

  f1.setSize(200,100); f2.setSize(200,200);

  f1.setVisible(true); f2.setVisible(true);

 }

 public static void main(String[] a){ new Layout(); }

}

3. Differentiate between method overloading and method overriding. Write program to show overriding.

Difference

Overloading

Overriding

Same class

Parent–child class

Different parameters

Same parameters

Compile-time

Run-time

Overriding Program

class A{ void show(){ System.out.println("A"); } }

class B extends A{

 void show(){ System.out.println("B"); }

 public static void main(String[] a){

  A o=new B(); o.show();

 }

}

4. What is exception handling? Write program to show array index out of bound exception.

Exception Handling

Exception handling is a mechanism to handle runtime errors and prevent program termination.

Program

class Test{

 public static void main(String[] a){

  try{

   int x[]={1};

   System.out.println(x[5]);

  }

  catch(Exception e){

   System.out.println("Error");

  }

 }

}

5. Define interface. Why interface is used? Write example program.

Interface

An interface is a collection of abstract methods used to achieve abstraction and multiple inheritance.

Uses:
Multiple inheritance, loose coupling, full abstraction.

Example

interface A{ void show(); }

class B implements A{

 public void show(){ System.out.println("Done"); }

 public static void main(String[] a){

  new B().show();

 }

}

6. Difference between listener and adapter classes. Write program to handle any one event.

Difference

Listener

Adapter

Interface

Class

All methods needed

Optional methods

More code

Less code

Action Event Program

import java.awt.*;

import java.awt.event.*;

 

class Event extends Frame implements ActionListener{

 Event(){

  Button b=new Button("Click");

  b.addActionListener(this);

  add(b); setSize(200,200); setVisible(true);

 }

 public void actionPerformed(ActionEvent e){

  System.out.println("Clicked");

 }

 public static void main(String[] a){ new Event(); }

}

OR

JDBC program to create MySQL database mydb_2025

import java.sql.*;

 

class JDBC{

 public static void main(String[] a)throws Exception{

  Connection c=DriverManager.getConnection(

   "jdbc:mysql://localhost:3306/","root","");

  c.createStatement().execute(

   "create database mydb_2025");

 }

}

 

  

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