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();
 }
 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() {
 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 ans = a-b;
 }
 });
 mul.addActionListener(new ActionListener() {
 int ans = a*b;
 }
 });
 div.addActionListener(new ActionListener() {

 if(b == 0)
 showStatus( "can't be divided by 0" );
 else{
 int ans = a/b;
 }}
 });
 }}

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);
 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 {
InputStreamReader(socket.getInputStream()));
 out = br2.readLine();
 System.out.println("> Client says : " + out);
 } while (!out.equals("END"));
 }
 }
 }
 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 {

 socket = new Socket("localhost", 9876);
 t1.start();
 t2.start();

 }
 }
 try {

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

References:
 Herbert Schildt
 Stackoverflow.com

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