Java practice programs for beginners

JAVA PRACTICE PROGRAMS FOR BEGINNERS WITH SOLUTIONS by Ishan Sharma

public class javaprog1{ String str1,str2,str3; static int count; javaprog1(){ count++; } javaprog1(String s1){ str1 = s1; count++; } javaprog1(String s2,String s3){ str2 = s2; str3 = s3; count++; } WAP program to show constructor overloading using static member

public static void main(String args[]){ javaprog1 obj1 = new javaprog1(); javaprog1 obj2 = new javaprog1("string 1"); javaprog1 obj3 = new javaprog1("string 2","string 3"); System.out.println("number of times static variable used : "+count); } }.

WAP to implement multilevel inheritance and method overriding  class parent{   public void function(){  System.out.println("In parent class");  }  }  class child1 extends parent{   public void function(){  System.out.println("In child1 class");  }  }

 class child2 extends parent{   public void function(){  System.out.println("In child2 class");  }  }  public class javaprog2{  public static void main(String args[]){  parent obj = new parent();  obj.function();   child1 obj_c1 = new child1();  child2 obj_c2 = new child2();   obj = obj_c1;  obj.function();   obj = obj_c2;  obj.function();  }  }

WAP to implement interface class and show use of package  // JavaProg3 is a different  //package  package JavaProg3;  public interface javaprog3{   public void print(String str_arg);  }  import JavaProg3.*;  public class javaprog4 implements javaprog3{  public void print( String str_arg){   System.out.println(str_arg);  }   public static void main(String args[]){  javaprog4 obj = new javaprog4();   obj.print(args[0]);  }  }

exception handling and create your own exception  import JavaProg3.*;  public class javaprog4 implements javaprog3{  public void print( String str_arg[]){   try{  for(int i=0;i<10;i++)  System.out.println(str_arg[i]+"n");  }catch(Exception e){  System.out.println("exception caught and re-thrown");  throw(e);  }  }  public static void main(String args[]){  javaprog4 obj = new javaprog4();   try{  obj.print(args);  } catch(Exception e){  System.out.println(e);  }  }  }

WAP to implement 3 threads such that 1st sleeps for 200ms, 2nd for 400ms and 3rd for 600ms  class NewThread implements Runnable {  Thread t;int time;  NewThread(String str,int time1) {  time = time1;  t = new Thread(this, str);  System.out.println(t);  t.start();  }  public void run() {  try {  for(int i = 5; i > 0; i--) {  System.out.println(t);  Thread.sleep(time);  }  } catch (InterruptedException e) {  System.out.println("Child interrupted.");  }  System.out.println("Exiting"+t);  }  }  class ThreadDemo {  public static void main(String args[]) {

 try {  NewThread t1 = new NewThread("thread1",200);  NewThread t2 = new NewThread("thread2",400);  NewThread t3 = new NewThread("thread3",600);  }catch (Exception e) {  System.out.println(" thread interrupted."+e);  }  }  }

WAP to create applet of moving banner  import java.awt.*;  import java.applet.*;  public class ParamBanner extends Applet implements Runnable {  String msg=" Hello Java...... ";  Thread t = null;  int state;  boolean stopFlag;  public void start() {  setBackground(Color.blue);  setForeground(Color.green);  Font currentFont = new Font("TimesRoman", Font.PLAIN, 40);  setFont(currentFont);  t = new Thread(this);  stopFlag = false;  t.start();  }  public void run() {  char ch;

 for( ; ; ) {  try {  repaint();  Thread.sleep(150);  ch = msg.charAt(0);  msg = msg.substring(1, msg.length());  msg += ch;  if(stopFlag)  break;  } catch(InterruptedException e) {}  }  }  public void paint(Graphics g) {  g.drawString(msg, 50, 30);  }  }

WAP to make a simple calculator  import java.awt.*;  import java.awt.event.*;  import javax.swing.*;  public class calculator extends JApplet {  JTextField jtf1,jtf2;  JButton add = new JButton("add");  JButton sub = new JButton("sub");  JButton mul = new JButton("mul");  JButton div = new JButton("div");  public void init() {  SwingUtilities.invokeAndWait(  new Runnable() {  public void run() {  makeGUI();  }  }  );  } catch (Exception exc) {  System.out.println("Can't create because of " + exc);  }  }  private void makeGUI() {

 setLayout(new FlowLayout());  jtf1 = new JTextField(5);  add(jtf1);  jtf2 = new JTextField(5);  add(jtf2);  add(add);  add(sub);  add(mul);  add(div);  add.addActionListener(new ActionListener() {  public void actionPerformed(ActionEvent ae) {  int a = Integer.parseInt(jtf1.getText());  int b = Integer.parseInt(jtf2.getText());  int ans = a+b;  StringBuilder str = new StringBuilder();  str.append(ans);  String str1 = str.toString();  showStatus( str1 );  }  });  sub.addActionListener(new ActionListener() {  public void actionPerformed(ActionEvent ae) {

 int a = Integer.parseInt(jtf1.getText());  int b = Integer.parseInt(jtf2.getText());  int ans = a-b;  StringBuilder str = new StringBuilder();  str.append(ans);  String str1 = str.toString();  showStatus( str1 );  }  });  mul.addActionListener(new ActionListener() {  public void actionPerformed(ActionEvent ae) {  int a = Integer.parseInt(jtf1.getText());  int b = Integer.parseInt(jtf2.getText());  int ans = a*b;  StringBuilder str = new StringBuilder();  str.append(ans);  String str1 = str.toString();  showStatus( str1 );  }  });  div.addActionListener(new ActionListener() {  public void actionPerformed(ActionEvent ae) {

 int a = Integer.parseInt(jtf1.getText());  int b = Integer.parseInt(jtf2.getText());  if(b == 0)  showStatus( "can't be divided by 0" );  else{  int ans = a/b;  StringBuilder str = new StringBuilder();  str.append(ans);  String str1 = str.toString();  showStatus( str1 );  }}  });  }}

Build a client server chat application  //server class  import java.io.BufferedReader;  import java.io.InputStreamReader;  import java.io.PrintWriter;  import java.net.*;  public class server implements Runnable {  ServerSocket serversocket;  BufferedReader br1, br2;  PrintWriter pr1;  Socket socket;  Thread t1, t2,t3;  String in="",out="";  public server() {  try {  t1 = new Thread(this);  t2 = new Thread(this);  t3 = new Thread(this);  serversocket = new ServerSocket(9876);  System.out.println("> Server is waiting for client to connect ");  socket = serversocket.accept();  System.out.println("Client connected with Ip " + socket.getInetAddress().getHostAddress());  t1.start();  t2.start();  } catch (Exception e) {  }  } public void run() {  try {

 if (Thread.currentThread() == t1) {  do {  br1 = new BufferedReader(new InputStreamReader(System.in));  pr1 = new PrintWriter(socket.getOutputStream(), true);  in = br1.readLine();  pr1.println(in);  } while (!in.equals("END"));  } else {  do {  br2 = new BufferedReader(new InputStreamReader(socket.getInputStream()));  out = br2.readLine();  System.out.println("> Client says : " + out);  } while (!out.equals("END"));  }  } catch (Exception e) {  }  }  public static void main(String[] args) {  new server();  }  }

 //client class  import java.io.BufferedReader;  import java.io.InputStreamReader;  import java.io.PrintWriter;  import java.net.*;  public class Client implements Runnable {  BufferedReader br1, br2;  PrintWriter pr1;  Socket socket;  Thread t1, t2,t3;  public Client() {  try {  t1 = new Thread(this);  t2 = new Thread(this);   socket = new Socket("localhost", 9876);  t1.start();  t2.start();   } catch (Exception e) {  }  }  public void run() {  try {

 if (Thread.currentThread() == t2 ) {  do {  br1 = new BufferedReader(new InputStreamReader(System.in));  pr1 = new PrintWriter(socket.getOutputStream(), true);  in = br1.readLine();  pr1.println(in);  } while (!in.equals("END"));  } else {  do {  br2 = new BufferedReader(new InputStreamReader(socket.getInputStream ()));  out = br2.readLine();  System.out.println("> Server says : " + out);  } while (!out.equals("END"));  }  } catch (Exception e) {  }  }  public static void main(String[] args) {  new Client();  }  }

References:  Herbert Schildt  Stackoverflow.com

Java practice programs for beginners

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