Info-Grade: Java

Write a Java program to create Rectangle class with data member length and breadth. Include methods getData() and displayArea() in the class. Finally create an object of Rectangle class and display its area.

 

import java.util.Scanner; 
class Rectangle4{
	int l, b; 
	void getData(){
		Scanner in = new Scanner(System.in); 
		System.out.print("Enter length : "); 
		l=in.nextInt(); 

		System.out.print("Enter breadth : "); 
		b=in.nextInt(); 
	}

	void displayArea(){
		int a; 
		a = l*b; 
		System.out.println("Area = "+a); 
	}

	public static void main(String args[]){
		Rectangle4 obj = new Rectangle4();
		obj.getData(); 
		obj.displayArea();  
	}
}

Define the term class and object? How can you create class and object in Java? Explain with example.

Class is a blueprint to template of real world objects that specifies what data and what methods will be included in object of the class. Class is also called description group of object objects having similar properties. A class is also called user defined data type or programmers defined data type because we can define new data types according to our need by using classes.

Objects are instances of class. We can say that object is variable of class type. Memory for instance declaration rather at the time of class declaration rather than time of object creation. Thus we can say that objects have physical existence and classes are only concepts.

Declaring Classes
Syntax:
[Access Modifier] className{
// body
}

Creating Object
Syntax:
[className] [objectName] = new [className]();

Program

 
class Demo{
 void display(){
  System.out.println("Class Example");
 }
 public static void main(String args[]){
  Demo obj = new Demo(); 
  obj.display(); 
 }
}

What do you mean by JSP? Write a program in the JSP to display Message "I Love Programming" 100 times.

JSP is a Java Server side technology that does all the processing at server. It is used for creating dynamic web application using Java as programming language.

JSP Program to print "I Love Programming" 100 times.

Program

 
<!DOCTYPE html>
<html> 
<head> 
 <meta http-equiv="Content-Type" content="text/html" charset=UTF-8">
 <title> A simple JSP program </title> 
</head> 
<body> 
 <h1> Displaying "I love Programming 100 times !!" </h1> 
 <table> 
  <% for(int i=1; i<=100; i++){ %> 
   <tr> <td> I Love Programming </td> </tr> 
  <% } %>
 </table> 
</body> 
</html>

Write a program using swing components to find simple interest. Use text fields for input and output. Your program should display the result when the user presses a button.

Output of the given Java program

Program

 

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;       

class PTR extends JFrame implements ActionListener //implement listener interface
{
 JTextField t1, t2, t3, t4;
 JLabel l1,l2,l3, l4;
 JButton b1; 
 public PTR() 
 {
  super("Handling Action Event");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);  
        l1 = new JLabel("Enter P :");
  l2 = new JLabel("Enter T :");
  l3 = new JLabel("Enter R : ");
  l4 = new JLabel("Interest : ");
  t1 = new JTextField(10);
  t2 = new JTextField(10);
  t3 = new JTextField(10);
  t4 = new JTextField(10); 
  b1 = new JButton("Calculate");
  
  setLayout(new FlowLayout(FlowLayout.LEFT,150,10));
        add(l1);
  add(t1);
  add(l2);
  add(t2);
  add(l3);
  add(t3);
  add(l4);
  add(t4); 
  add(b1);

  b1.addActionListener(this);//Registering event

  setSize(400,300);
        setVisible(true);
 }
 
 public void actionPerformed(ActionEvent ae) //Handle Event
 {
  int p, t, r, si; 
  p = Integer.parseInt(t1.getText());   
  t = Integer.parseInt(t2.getText()); 
  r = Integer.parseInt(t3.getText());
  if(ae.getSource() == b1)
   si = (p*t*r)/100;
  else
   si = 0; 

  t4.setText(String.valueOf(si));
 }

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

How array can be declared in Java? Write a complete Java program to read two numbers from the user (where first number is less then second number) then find only even number between them.

Array is a data structure which contains of similar data type. We store only fixed set of elements in a java array. Array is used to store a collection of data, but it is often more useful to think of an array as a collection of variable of the same type.

To declare an array in a Java program, we must declare a variable to reference the array and we most specify the type of array the variable can reference.
Syntax:
dataType[] arrayRefVar;
or
dataType arrayRefVar[];

Program

 

import java.util.Scanner; 
class EvenArray{
     public static void main(String args[]){
 Scanner in = new Scanner(System.in); 
 int x, y; 
 System.out.print("Enter First Number : "); 
 x = in.nextInt(); 
 System.out.print("Enter Second Number : "); 
 y = in.nextInt(); 

 for(int i=x; i<=y; i++){
      if(i%2==0){
     System.out.println(i); 
      }
 }
     }
}

What is thread in Java? Difference between process and thread? Life cycle of thread.

The thread is a lightweight process that means one single program can be divided into small threads which will execute concurrently for fast execution of task. We can say that thread is a sub process of a process.

A thread is an independent path of execution within a program. Many thread can run concurrently within a program. Every threads in Java is created and controlled by the java.lang thread class. A java program can have many threads, and these threads can run currently, either synchronously or asynchronously.

- Threads are lightweight compared to process.

Difference between thread and process

Process	Thread
- A Process is an instance of a program. It contains a threads.	- Threads are the parts of process. It cannot contain a process.
- Process run in its separate.	- Thread run in shared memory spaces.
- Process is controlled by the operating system.	- Threads a re controlled by programmer in a program.
- Processes are independent.	- Threads are dependent.
- New processes require duplication of the parent process.	- New threads are easily created.
- Process require more time for context switching as they are more heavy.	- Threads require less time for context switching as they are lighter then process.
- Process require more resources then threads.	- Threads generally need less resources than process.
- Process require more time for termination.	- Threads require less time for termination.

Life cycle of threads

New
The thread is in new state if you create an instance of thread class but before the invocation of start() method.

Runnable
A thread in the runnable state is executing the Java virtual machine but it may be waiting for other resources from the operating system such as processor.

Running
The thread is in running state if the thread scheduler has selected it.

Blocked (Non Runnable)
It is the state when the thread is still alive, but is currently not eligible to run.

Terminated
A thread is in terminated or dead state when its run() method exists.

Java Database Connectivity Simple Example ( Download JDBC Driver and MySql)

Write a Java program to create a form with student id, student name, level, and two button insert and clear. Handle the event such that buttons with perform the operations as implied by their name.

 
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.sql.*;
class Student extends JFrame implements ActionListener
{
 JLabel sid,sname,slevel;
 JTextField tid,tname, tlevel;
 JButton insert, clear;
 JPanel p1,p2,p3,p4;
 Student()
 {
  setSize(400,250);
  setTitle("Students Data Entry");
  setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  
  p1=new JPanel();
  p2=new JPanel();
  p3=new JPanel();
  p4=new JPanel();

  setLayout(new BorderLayout());
  add(p1,BorderLayout.CENTER);
  add(p2,BorderLayout.SOUTH);
  p1.setLayout(new GridLayout(1,2));
  p1.add(p3);
  p1.add(p4);

  p3.setLayout(new FlowLayout(FlowLayout.LEFT, 75,20));
  p4.setLayout(new FlowLayout(FlowLayout.LEFT, 25,20));
  sid=new JLabel("Student ID");
  sname=new JLabel("Student Name");
  slevel=new JLabel("Level");
  p3.add(sid);
  p3.add(sname);
  p3.add(slevel);
  tid=new JTextField(10);
  tname=new JTextField(10);
  tlevel=new JTextField(10);
  p4.add(tid);
  p4.add(tname);
  p4.add(tlevel);
  p2.setLayout(new FlowLayout(FlowLayout.CENTER, 20,20));
  insert=new JButton("Insert");
  clear=new JButton("Clear");
  
                p2.add(insert);
  p2.add(clear);
  
  insert.addActionListener(this);
  clear.addActionListener(this);
    
  setVisible(true);
 }
 public void actionPerformed(ActionEvent ae)
 {
  Connection c=null;
  Statement s=null;
  try
  { 
   Class.forName("com.mysql.jdbc.Driver");
c = DriverManager.getConnection("jdbc:mysql://localhost/mydb","root", "raj");
   s=c.createStatement();
   if(ae.getSource()==insert)
   {
           int id;
                                String name, level;
    id=Integer.parseInt(tid.getText());   
                                name=tname.getText();
    level=tlevel.getText();
    
  String query="insert into studentdb values("+id+",'"+name+"',"+level+")";
    s.executeUpdate(query);
  JOptionPane.showMessageDialog(this,"Data is Recorded!!!!");
   
   }
   
   if(ae.getSource()==clear)
   {
                            tid.setText("");  
                            tname.setText(""); 
                            tlevel.setText("");
   }
  }
  catch(Exception e)
  {
                    System.out.println(e);
  }
 }
 public static void main(String a[])
 {
  new Student();
 }
}

Download Code File

Download JDBC Driver and MySql

Java Swing | Internal Frames |

A JInternalFrame is a container that looks much like a JFrame. The key difference is that internal frames can only exist within some other Java container.
Thus, we must add an internal frame to a container (usually a JDesktopPane). The following list summarizes the rules for using internal frames.

We can create internal frames by using any one of following constructors.

Example:

 
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
class IFDemo extends JFrame
{
	JDesktopPane dp;
	JInternalFrame iframe;
	JTextField tb;
	JLabel lb;
	IFDemo()
	{
		setSize(400,300);		
		setDefaultLookAndFeelDecorated(true);
		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		setVisible(true);
		dp=new JDesktopPane();
		iframe=new JInternalFrame("Internal Frame",true,true,true,true);
		iframe.setSize(200,200);
		iframe.setLocation(50,50);
		dp.add(iframe);
		add(dp);
		lb=new JLabel("Email");
		tb=new JTextField(10);
		iframe.setLayout(new FlowLayout(FlowLayout.CENTER));
		iframe.add(lb);
		iframe.add(tb);
		iframe.setVisible(true);		
	}	
	public static void main(String args[]) 
	{
		IFDemo frame=new IFDemo();		
	}
}

Java Swing | Menu Bar Example

To create menus, we need to follow the following steps:
- First, A JMenubar is created
- Then, we attach all of the menus to this JMenubar.
- Then we add JMenuItem to the JMenu.
- The JMenubar is then added to the frame by using setJMenuBar() method.

JMenuBar
We can create menu bar by using following constructor:
JMenuBar()

JMenu
It can be created by using following constructors:
JMenu()
JMenu(String)

 
import javax.swing.*; 

class Menu extends JFrame{ 
 JMenuBar mb; 
 JMenu file, edit, data, name; 
 JMenuItem open, save, sas, cut, copy, paste; 
 JCheckBoxMenuItem  raju, indra;
 
 Menu(){ 
  setTitle("Menu Demo"); 
  setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 

  mb=new JMenuBar(); 
  file=new JMenu("File"); 
  edit=new JMenu("Edit"); 
  data=new JMenu("Data"); 
  name=new JMenu("Name"); 

  open=new JMenuItem("Open"); 
  save=new JMenuItem("Save"); 
  sas=new JMenuItem("Save As"); 
  cut=new JMenuItem("Cut"); 
  copy=new JMenuItem("Copy"); 
  paste=new JMenuItem("Paste");

  raju=new JCheckBoxMenuItem("Raju"); 
  indra=new JCheckBoxMenuItem("Indra"); 

  file.add(open);  
  file.add(save); 
  file.add(sas); 

  edit.add(cut); 
  edit.add(copy); 
  edit.add(paste); 

  data.add(name); 

  name.add(raju); 
  name.add(indra); 

  mb.add(file); 
  mb.add(edit); 
  mb.add(data); 

  setJMenuBar(mb); 
  setSize(500, 500); 
  setVisible(true); 
 }

 public static void main(String args[]){
  new Menu(); 
 }
}

Java Solution Exam Oriented

1. Define constructor? Explain constructor overloading with suitable example.

Solution:

Constructor in java is special type of method that is used to initialize the object. Java constructor is invoked at the time of object creation. It constructs the values i.e. provides data for the object therefore it is known as constructor.

More than one constructor with different signature in a class is called constructor overloading.

 
public class Student{
 int roll, marks; 
 String name;

 Student(int r, String n, int m){
  roll = r; 
  name = n; 
  marks = m; 
 }

 Student(int r, int m, String n){
  roll = r; 
  name = n; 
  marks = m;  
 }

 void displaInfo(){
  System.out.println(roll+"\t"+name+"\t"+marks);
 }
 public static void main(String args[]){
  Student s1 = new Student(1, "Ram", 56); 
  Student s2 = new Student(2, 89, "Shyam"); 

  System.out.println("Roll \t Name \t Marks");
  s1.displaInfo();
  s2.displaInfo(); 
 }
}

2. How class is different then object ? Write a program to create Employee class with data members employee id, employee name, and salary. Also put necessary member function for reading and display objects. Create two objects of employee class and then read and display their details.

Solution:
Classes and objects are the fundamental components of OOP's. A class is an entity that determines how an object will behave and what the object will contain. In other words, it is a blueprint or a set of instruction to build a specific type of object.

Object is an instance of a class. It determines the behavior of the class. Memory is allocated for data members of class when object is created.

 
import java.util.Scanner; 
class Employee{
 int id, salary;
 String name; 

 public void getData(){
  Scanner in = new Scanner(System.in); 
  System.out.println("\nEnter the Following Info of Employee"); 
  System.out.print("Employee ID : "); 
  id = in.nextInt(); 
  System.out.print("Employee Name : "); 
  name = in.next(); 
  System.out.print("Employee Salary : "); 
  salary = in.nextInt(); 
 }

 public void displayData(){
  System.out.println("\n***Employee Details***"); 
  System.out.println("ID = "+id); 
  System.out.println("Name = "+name); 
  System.out.println("Salary = "+salary); 
 }
 
 public static void main(String args[]){
  Employee em1 = new Employee(); 
  Employee em2 = new Employee(); 

  em1.getData();
  em1.displayData(); 

  em2.getData();
  em2.displayData(); 
 }
}

3. Write a program to create a form first number second number, and result, and two buttons and add subtract. Handle the events such that clicking on and button computes addition and clicking on subtract performs subtraction.

Solution:

 
import java.awt.*;
import javax.swing.*; 
import java.awt.event.*; 

class Calc extends JFrame implements ActionListener{
 
 JLabel l1, l2, l3; 
 JTextField t1, t2, t3; 
 JButton b1, b2; 

 Calc(){
  
  super("Handling Action Event"); 
  l1 = new JLabel("Enter First Number"); 
  l2 = new JLabel("Enter Second Number"); 
  l3 = new JLabel("Result"); 

  t1 = new JTextField(10); 
  t2 = new JTextField(10); 
  t3 = new JTextField(10); 

  b1 = new JButton("Add"); 
  b2 = new JButton("Subtract"); 

  setLayout(new FlowLayout(FlowLayout.LEFT,90,10));
  add(l1); 
  add(t1); 
  add(l2); 
  add(t2); 
  add(l3); 
  add(t3); 
  add(b1); 
  add(b2); 

  b1.addActionListener(this); 
  b2.addActionListener(this); 

  setSize(300, 300); 
  setVisible(true);
  setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
 }

 public void actionPerformed(ActionEvent ae){
  int x, y, z; 
  x=Integer.parseInt(t1.getText()); 
  y=Integer.parseInt(t2.getText()); 
  if(ae.getSource() == b1){
   z = x + y; 
  }else{
   z = x - y; 
  }

  t3.setText(String.valueOf(z)); 
 }

 public static void main(String args[]){
  new Calc(); 
 }
}

4. What are different types of exceptions? Explain use of try.....catch and finaly with example.

Solution:
Exceptions are the unwanted errors or bugs or events that restrict the normal execution of a program. In such cases we get a system generated error message. An error message is displayed on the screen. There are mainly two types of exceptions: They are :

Built-In Exception
User-Defined Exception

Built-in exceptions are the exceptions which are available in Java libraries. These exceptions are suitable to explain certain error situations. Some Built-in exceptions are :

Arithmetic Exception
ArrayIndexOutOfBoundsException
ClassNotFoundException
FileNotFoundException
IOException etc.

Sometimes, the built-in exceptions in Java are not able to describe a certain situation. In such cases, user can also create exceptions which are called ‘user-defined Exceptions’.

Use of Try ... Catch and Finally

A try block is used to enclose the code that might throw an exception. It must be used within the method. Java try block must be followed by either catch or finally block.
Java catch block is used to handle the Exception. It must be used after the try block only.
Java finally block is a block that is used to execute important code such as closing connection, stream etc. Java finally block is always executed whether exception is handled or not. Java finally block follows try or catch block.

Example

 

public class TestFinally{
    public static void main(String args[]){
        try{
            int x = 20/0; 
            System.out.println("Quoitent = "+x); 
        }
        catch(ArithmeticException e){
            System.out.println("e.getMessage"); 
        }
        finally{
            System.out.println("Finally block is always executed"); 
        }
        System.out.println("Rest of the Codes .... "); 
    }
}

5. Write down the the steps for writing client and server program by using UDP?

Solution
UDP is a Datagram, It is a connection less ,independent , self contained protocol. Bulk Data are send and receive as packets from using UDP. Steps to write client and server program by using UDP are as follows:
Steps for Writing Client Program
Step1: Get Datagram Socket
DatagramSocket ds=new DatagramSocket(port)
Step2: Send Request
DatagramPacket p=new DatagramPacket(byte[],length, inetaddress,port)
ds.send(p)
Step3: Get Response
p=new DatagramPacket(buf,buf.length)
ds.receive(p)
Step4: Display Response
String s=new String(p.getData());
System.out.println(“Server:”+s);
Step 5: Close the Socket
ds.close();

Steps for Writing Server Program
Step1: Get Datagram Socket
DatagramSocket ds=new DatagramSocket(port)
Step2: Receive Request
byte[] buf=new byte[256]
DatagramPacket p=new DatagramPacket(buf,buf.length)
ds.receive(p)
Step3: Send Response
String s=new String(“Hello Client”);
buf=s.getBytes()
ds.send(p)
Step 4: Close the Socket
ds.close();

5. Write a Java Swing Program to design the following menu bar.

Solution:


import javax.swing.*;  

class MenuDemo extends JFrame{
 
 JMenuBar mb; 
 JMenu file, edit, format; 
 JMenuItem open, save, save_as, exit, undo, redo; 

 MenuDemo(){
  setTitle("Menu Bar"); 
  setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 

  mb=new JMenuBar(); 

  file=new JMenu("File"); 
  edit=new JMenu("Edit"); 
  format=new JMenu("Format"); 

  open=new JMenuItem("Open"); 
  save=new JMenuItem("Save"); 
  save_as=new JMenuItem("Save As"); 
  exit=new JMenuItem("Exit"); 
  undo=new JMenuItem("Undo"); 
  redo=new JMenuItem("Redo"); 

  file.add(open); 
  file.add(save); 
  file.add(save_as); 
  file.add(exit); 

  edit.add(undo); 
  edit.add(redo); 

  mb.add(file); 
  mb.add(edit); 
  mb.add(format); 

  setJMenuBar(mb); 
 
  setSize(300, 200); 
  setVisible(true); 
 }

 public static void main(String args[]){
  new MenuDemo(); 
 }
}