Java Program to Hibernate Windows Operating System

Do you want to hibernate your Windows computer using java program? This is a java program to hibernate Windows operating System. If you execute this java program, it will hibernate your Windows computer instantly. The following is the java code to hibernate Windows:

try
 {
 Runtime.getRuntime().exec("shutdown /h");
 } catch (IOException ex) {}

How to Launch a Application or Executable Using Java Code with Command Line Arguments

In this post, we shall see how to launch an application with its command line arguments using Java code. Most applications take path of a file as command-line argument to open it. If we give path of an image file to mspaint application as command-line argument, the image will be opened in paint. The following java program launches mspaint with a command-line argument which is a path to an image.

 try
 {
 Runtime.getRuntime().exec("C:\\Windows\\System32\\mspaint.exe \"C:\\Users\\Shareef\\Desktop\\flower.jpg\"");
 } catch (IOException ex) {}

Arguments are separated by spaces. If a command-line argument contains space within it (such as a space in a path), it is recommended to enclose it within brackets.

How to Use printf, println and print Methods in Java

To display output on terminal, we can use print, println or printf methods (functions) in Java. These methods are available in the static PrintStream object System.out. We will see the use of each method in detail below.

print()

This method displays instance of any data type (Object, int, float, double, String, char etc) on terminal display. If you want to display something in a new line, you have to prefix and/or suffix the new line character with the content. An example is as follows:

int a=600;
System.out.print("\nThis is a line\n");
System.out.print(a);
System.out.print("\n");

The above code displays the first string and the number 600 in two separate lines

println()

Unlike print(), println() method appends a new-line  character to the end of the content. Just like print() method, println() method also has various overloaded definitions so that it could take variable of any type as argument. If the println() method is called without any arguments, it will simply output a new line character. The following code and its output will give you an idea.

System.out.println("Hi this is first line");
System.out.println();
System.out.println("Above this, an empty println() was called");

Output:

Hi this is first line

Above this, an empty println() was called

printf()

The printf() method is similar to the printf() function in stdio.h header in c language. You can use System.out.printf() method to format the srting just as you do in c language. This method writes a formatted string to this output stream using the specified format string and arguments. The usage is as follows:

System.out.format(format, args);

Let us see a few examples:

String s="Shareef";
int number=7343543;
System.out.printf("My name is %s and number is %d",s,number);
System.out.printf("\nThe following is multiplication table of 9:\n");
for(int i=1;i<=10;i++)
    System.out.printf("%2d * %1d = %2d\n",i,9,i*9);

The output of above code is:

My name is Shareef and number is 7343543The following is multiplication table of 9:
 1 * 9 =  9
 2 * 9 = 18
 3 * 9 = 27
 4 * 9 = 36
 5 * 9 = 45
 6 * 9 = 54
 7 * 9 = 63
 8 * 9 = 72
 9 * 9 = 81
10 * 9 = 90

Making of Tetris Game in Java

Here in this post, i will share a Java program to make a Tetris game. I have already wrote a post on how to make a tetris game in C language. I have discussed the data structures used in the program in that post. The Java program is almost similar to it. The description is available in this post: Making of Tetris Game in C.

The following video shows the java code in action:


The tetris game Java source code is as follows:

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.util.Random;
import javax.swing.JFrame;
import javax.swing.JOptionPane;



public class Tetris extends JFrame{

boolean stopthread=false;
int SIZE_HORIZ=13;
int SIZE_VERTI=35;
Graphics g;
boolean waitnow=false;
int[][] board=new int[SIZE_VERTI][SIZE_HORIZ];
int t_[]={1,0,1,1,1,2,2,1};
int t_90[]={0,1,1,0,1,1,2,1};
int t_180[]={0,1,1,0,1,1,1,2};
int t_270[]={0,1,1,1,1,2,2,1};
int l_[]={0,2,1,0,1,1,1,2};
int l_90[]={0,1,1,1,2,1,2,2};
int l_180[]={1,0,1,1,1,2,2,0};
int l_270[]={0,0,0,1,1,1,2,1};
int s_[]={0,0,0,1,1,0,1,1};
int z_[]={1,1,1,2,2,0,2,1};
int z_90[]={0,1,1,1,1,2,2,2};
int i_ver[]={0,1,1,1,2,1,3,1};
int i_hor[]={1,0,1,1,1,2,1,3};
String scorestr;
Random rand=new Random(System.currentTimeMillis());
Color colors[]={Color.BLUE,Color.GREEN,Color.MAGENTA,Color.RED,Color.YELLOW};
File HighScore;
Color bgcolor=Color.WHITE;
/*
Numbering for blocks:
(values of fallingBlockNumber)
0=T
1=L
2=S
3=Z
4=I
*/
int [] blockarray;
int fallingblockNum;
int fallingBlockVersion=0;
int fallingBlockRow=0;
int fallingBlockCol=0;
int startdelay=200;
int motiondelay;
int scoreInc=5;
int myscore=0;
int tversion;
boolean spawn=true;
int scorespeedctrl=0;
int timehalving=0;
String highscoreholder;
int highscore;
KeyListener kl;

public Tetris()
{
int i,j;
startdelay=250;
scoreInc=5;
myscore=0;
motiondelay=startdelay;
NextBlock();
for(i=0;i<35;i++)
    for(j=0;j<13;j++)
 board[i][j]=0;
setDefaultCloseOperation(EXIT_ON_CLOSE);
setSize(480,500);
setResizable(false);
setLocationRelativeTo(null);
HighScore=new File(System.getProperty("java.io.tmpdir")+File.separator+"TetrisHighScore");
try{
if(HighScore.exists())
    {
    BufferedReader br=new BufferedReader(new FileReader(HighScore));
    highscoreholder=br.readLine();
    highscore=Integer.parseInt(br.readLine());
    br.close();
    }
else
    {
    highscoreholder=null;
    highscore=0;
    }
}catch(Exception ex){}
kl=new KeyListener() {
    @Override
    public void keyTyped(KeyEvent e) {}

    @Override
    public void keyPressed(KeyEvent e) {
    
        if(!spawn&&!waitnow)
 {
            waitnow=true;
            int key=e.getKeyCode();
     if(key==KeyEvent.VK_UP)//up
  {
  if(fallingblockNum==0||fallingblockNum==1)
      tversion=(fallingBlockVersion+1)%4;
  else if(fallingblockNum==4||fallingblockNum==3)
      tversion=(fallingBlockVersion+1)%2;

  if(fallingblockNum!=2&&isDrawable(fallingBlockRow,fallingBlockCol,tversion))
      {
      clearOldBlockVersion(g);
      fallingBlockVersion=tversion;
      blockarray=getFallingBlockArray();
      drawNewBlockVersion(g);
      }
  }
     else if(key==KeyEvent.VK_LEFT)//left
  {
  if(isDrawable(fallingBlockRow,fallingBlockCol-1,fallingBlockVersion))
      {
      clearOldBlockVersion(g);
      fallingBlockCol--;
      drawNewBlockVersion(g);
      }
  }
     else if(key==KeyEvent.VK_RIGHT)//right
  {
  if(isDrawable(fallingBlockRow,fallingBlockCol+1,fallingBlockVersion))
      {
      clearOldBlockVersion(g);
      fallingBlockCol++;
      drawNewBlockVersion(g);
      }
  }
     else if(key==KeyEvent.VK_DOWN)//down
  {
  if(isDrawable(fallingBlockRow+1,fallingBlockCol,fallingBlockVersion))
      {
      clearOldBlockVersion(g);
      fallingBlockRow++;
      drawNewBlockVersion(g);
      }
  }
            waitnow=false;
 }
    }
    @Override
    public void keyReleased(KeyEvent e) {}
};
th.start();
addKeyListener(kl);
}

void NextBlock()
{
fallingblockNum=rand.nextInt(5);
if(fallingblockNum==0||fallingblockNum==1)
 fallingBlockVersion=rand.nextInt(4);
else if(fallingblockNum==4||fallingblockNum==3)
 fallingBlockVersion=rand.nextInt(2);
else
 fallingBlockVersion=0;
fallingBlockRow=0;
fallingBlockCol=5;
blockarray=getFallingBlockArray();
}

int[] getFallingBlockArray()
{
int a=fallingblockNum*10+fallingBlockVersion;
switch(a)
    {
    case 0:return (t_);
    case 1:return (t_90);
    case 2:return (t_180);
    case 3:return (t_270);
    case 10:return (l_);
    case 11:return (l_90);
    case 12:return (l_180);
    case 13:return (l_270);
    case 20:return (s_);
    case 30:return (z_);
    case 31:return (z_90);
    case 40:return (i_hor);
    case 41:return (i_ver);
    }
return (i_ver);
}

boolean isDrawable(int newrow,int newcol,int blockversion)
{
int i,tempversion;
boolean flag=true;
tempversion=fallingBlockVersion;
fallingBlockVersion=blockversion;
blockarray=getFallingBlockArray();
for(i=0;i<8;i+=2)
    {
    if(newrow+blockarray[i]>34||newrow+blockarray[i]<0)
 {
 flag=false;
 break;
 }
    if(newcol+blockarray[i+1]>12||newcol+blockarray[i+1]<0)
 {
 flag=false;
 break;
 }
    if(board[(newrow+blockarray[i])][(newcol+blockarray[i+1])]==2)
 {
 flag=false;
 break;
 }
    }
fallingBlockVersion=tempversion;
blockarray=getFallingBlockArray();
return flag;
}

void clearOldBlockVersion(Graphics g)
{
int i,r,c;
for(i=0;i<8;i+=2)
 {
 r=fallingBlockRow+blockarray[i];
 c=fallingBlockCol+blockarray[i+1];
 board[r][c]=0;
 g.setColor(bgcolor);
        g.fillRect(8+c*13,32+r*13,14,14);
 }
}

void drawNewBlockVersion(Graphics g)
{
int i,r,c;
for(i=0;i<8;i+=2)
 {
 r=fallingBlockRow+blockarray[i];
 c=fallingBlockCol+blockarray[i+1];
 board[r][c]=1;
        g.setColor(colors[fallingblockNum]);
 g.fillRect(8+c*13,32+r*13,13,13);
        g.setColor(Color.BLACK);//cyan,orange
 g.drawRect(8+c*13,32+r*13,13,13);
 }
}
boolean isGameOver(Graphics g)
{
if(isDrawable(0,5,fallingBlockVersion)==false)
    return true;
drawNewBlockVersion(g);
if(isAtBottom())
    return true;
return false;
}

boolean isAtBottom()
{
int i,max=0,ti,tj;
for(i=0;i<8;i+=2)
    if(blockarray[i]>max)
 max=blockarray[i];
if(fallingBlockRow+max>=34)
 return true;
for(i=0;i<8;i+=2)
    {
    ti=blockarray[i]+fallingBlockRow;
    tj=blockarray[i+1]+fallingBlockCol;
    if(board[ti+1][tj]==2)
       return true;
    }
return false;
}

void showScore(Graphics g)
{
int left,top;
left=getWidth()-100;
top=getHeight()/2;
g.setColor(bgcolor);
g.fillRect(left,top,80,70);
g.setColor(Color.RED);
g.setFont(new Font("Arial",Font.BOLD,14));
g.drawString("Score: "+Integer.toString(myscore),left,top+20);
}

void CollapseFilledRow(Graphics g)
{
int i,j,k,sum,copyskipover=0,r;
for(i=34;i>=0;)
    {
    sum=0;//full flag
    for(j=0;j<13;j++)
 sum+=board[i][j];
    if(sum==2*13)//row full
 {
 myscore+=scoreInc;
 copyskipover++;
 }
    if(sum==0)
 break;
    i--;
    if(copyskipover>0)
 {
 for(j=0;j<13;j++)
     {
     r=i+copyskipover;
     board[r][j]=board[i][j];
     if(board[i][j]==0)
  {
                g.setColor(bgcolor);
                g.fillRect(8+j*13,32+r*13,14,14);
  }
     else
  {
                g.setColor(Color.GREEN);
                g.fillRect(8+j*13,32+r*13,13,13);
                g.setColor(Color.BLACK);
                g.drawRect(8+j*13,32+r*13,13,13);
  }
     }
 }
    }
for(k=0;k<copyskipover;k++)
    {
    r=i+k;
    for(j=0;j<13;j++)
 {
 board[r][j]=0;
        g.setColor(bgcolor);
 g.fillRect(8+j*13,32+r*13,14,14);
 }
    }
showScore(g);
}


public static void main(String[] args)
{
Tetris tt=new Tetris();
tt.setVisible(true);
}

void GameOver(Graphics g)
{
stopthread=true;
g.setColor(Color.RED);
g.setFont(new Font("Arial",Font.BOLD,28));
String str="Game Over.";
g.drawString(str,getWidth()/2-10, getHeight()/2);
if(highscore>0)
    str="Highscore : "+highscoreholder+" - "+Integer.toString(highscore);
g.setFont(new Font("Arial",Font.BOLD,16));
g.drawString(str,getWidth()/2-30, getHeight()/2+80);
if(myscore>highscore)
    {
        highscoreholder=JOptionPane.showInputDialog("New high score. Enter your name:");
        highscore=myscore;
        try{
        if(!HighScore.exists())
            HighScore.createNewFile();
        BufferedWriter bw=new BufferedWriter(new FileWriter(HighScore));
        bw.write(highscoreholder);
        bw.newLine();
        bw.write(Integer.toString(highscore));
        bw.close();
        }catch(Exception ee){}
    }
}


Thread th=new Thread()
{
int i;
public void run()

{
try {
    while(!isShowing())
        Thread.sleep(1000);
    } catch (InterruptedException ex) {}
setOpacity(1f);
setBackground(bgcolor);
getContentPane().setBackground(bgcolor);
g=getGraphics();
g.setColor(Color.RED);
g.drawRect(6,30,13*13+6,35*13+6);
showScore(g);
while(!stopthread)
{
g.setColor(Color.RED);
g.drawRect(6,30,13*13+6,35*13+6);
while (waitnow)
    {
    try {
        Thread.sleep(20);
    } catch (InterruptedException ex) {}
    }
waitnow=true;
if(isAtBottom()&&!spawn)
 {
 for(i=0;i<8;i+=2)
     {
     board[fallingBlockRow+blockarray[i]][fallingBlockCol+blockarray[i+1]]=2;
     }
 spawn=true;
 CollapseFilledRow(g);
 }
    if(spawn)
 {
 NextBlock();
 blockarray=getFallingBlockArray();
 spawn=false;
 if(isGameOver(g))
     {
     GameOver(g);
     return;
     }
 }
    else
 {
 timehalving=(timehalving+1)%3;
 if(timehalving==2)
  {
  clearOldBlockVersion(g);
  fallingBlockRow++;
  drawNewBlockVersion(g);
  }
 }
    scorespeedctrl=(scorespeedctrl+1)%140;
    if(scorespeedctrl==0&&motiondelay>0)
 {
 motiondelay-=12;
 scoreInc+=2;
        if(motiondelay<0)
            motiondelay=0;
 }
    waitnow=false;
    try {
        Thread.sleep(motiondelay);
            } catch (InterruptedException ex) {}
}
}
};
}

Java Code to Restart Windows

Are you thinking how to restart Windows from Java. You can restart Windows operating system by executing a system command. You can restart windows by executing the system command shutdown /r /t 1. The following Java code will restart the windows computer when executed.

try {
    Runtime.getRuntime().exec("shutdown /r /t 1");
    } catch (IOException ex) {}

How to Schedule a Shutdown in Java - Java Code to Schedule a Shutdown

In this post, we will see how to schedule a shutdown in a computer using java program. For this, we execute the appropriate shutdown command after identifying the operating system. The following java code will schedule a shutdown after a 10 minute from execution of the code.

String os=System.getProperty("os.name").toLowerCase();
String command;
try
{
if(os.contains("windows"))
    {
    command="shutdown /s /t 600";
    }
else if(os.contains("linux")||os.contains("mac os x"))
    {
    command="shutdown -h +600";
    }
else
    throw new Exception("Unsupported OS");
Runtime.getRuntime().exec(command);
}catch(Exception ex){
JOptionPane.showMessageDialog(null,ex.getMessage());
}

How to Shutdown Computer from Java - Java Code to Shutdown Computer

Java program can cause a computer to shutdown. In order to shutdown a computer using java code, you should execute the shutdown command in that operating system. The shutdown command is different in Windows and Linux. So, we first check for the operating system. Then we execute appropriate shutdown command.

try {
            String command;
            String os = System.getProperty("os.name").toLowerCase();
            if (os.contains("linux") || os.contains("mac os x"))
                command = "shutdown -h now";
            else if (os.contains("windows"))
                command = "shutdown /p";
            else
                throw new Exception("Unsupported operating system.");
            
            Runtime.getRuntime().exec(command);
            System.exit(0);

        } catch (Exception ex) {
            JOptionPane.showMessageDialog(null, ex.getMessage());
        }

For Linux and Mac OS X, the command for immediate shutdown is shutdown -h now. But in Windows, it is shutdown /p. The above java code checks the operating system. Then it assumes appropriate shutdown command and then executes it. This java code can shutdown a computer.

How to Logoff or Sign Out Windows Using Java Code

You can sign out the current user account from windows using java code. Sign out, log out or logoff button can be created using simple lines of code. To logout from Windows operating system using java code, use the following code:

try {
        Runtime.getRuntime().exec("shutdown /l");
    } catch (IOException ex) {}

As the above code shows, we are simply executing a cmd command shutdown /l. It is actually running shutdown.exe with parameter /l to force logoff. If you add above code in the actionPerformed() function of a button, the button becomes a logoff button. The following video will show an example in which a simple button is made into a logout button.

Java Program for Animated Solution for Tower of Hanoi Puzzle Problem

This is a java program to solve towers of hanoi puzzle problem. This java program give solution for tower of hanoi problem with any number of disks. This program gives animated solution for tower of Hanoi problem. It demonstrates solving the tower of hanoi problem using animation in java.

The solution of hanoi problem given by this program is always optimal. You can enter the number of disks first. This lets you solve puzzle of any level of difficulty. The program is as follows.

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Graphics;
import java.util.Random;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;

public class HanoiAnimated extends JPanel{

static int tower[][];// the three towers' disks as stack
static int top[];//top of the three stacks
static int from,to;//moving 'from' tower number 'to' tower number
static int diskInAir;//number of disk moved (1 to n)
static int n,l,b,u;
static Color colors[]={Color.BLUE,Color.CYAN,Color.GREEN,Color.MAGENTA,Color.ORANGE,Color.PINK,Color.RED,Color.YELLOW};
public HanoiAnimated()
{
    tower=new int[3][10];
    top=new int[3];
}

static void push(int to, int diskno)
//putting disk on tower
{
tower[to-1][++top[to-1]]=diskno;
}

static int pop(int from)
//take topmost disk from tower
{
return(tower[from-1][top[from-1]--]);
}

Color getColor(int disknum)
{
return colors[disknum%8];
}

void drawStill(Graphics g)
{
int j,i,disk;
g.clearRect(0,0,getWidth(),getHeight());
for(j=1;j<=3;j++)
 {
 //draw tower
        g.setColor(Color.GRAY);
 g.fillRoundRect(j*l,u,5,b-u,1,1);
        
 //draw all disks on tower
 for(i=0;i<=top[j-1];i++)
  {
  disk=tower[j-1][i];
                g.setColor(getColor(disk));
  g.fillRect(j*l-15-disk*5,b-(i+1)*10,35+disk*10,10);
  }
 }
}

void drawFrame(Graphics g,int x,int y)
{
try{
drawStill(g);
g.setColor(getColor(diskInAir));
g.fillRect(x-15-diskInAir*5,y-10,35+diskInAir*10,10);
Thread.sleep(60);
}catch(InterruptedException ex){}
}

void animator(Graphics g)
//to show the movement of disk
{
int x,y,dif,sign;
diskInAir=pop(from);
x=from*l;
y=b-(top[from-1]+1)*10;
//taking disk upward from the tower
for(;y>u-20;y-=8)
 drawFrame(g, x, y);

y=u-20;
dif=to*l-x;
sign=dif/Math.abs(dif);
//moving disk towards a target tower
for(;Math.abs(x-to*l)>=24;x+=sign*12)
 drawFrame(g, x, y);
x=to*l;
//placing disk on a target tower
for(;y<b-(top[to-1]+1)*10;y+=8)
 drawFrame(g, x, y);
push(to,diskInAir);
drawStill(g);
}

void moveTopN(Graphics g, int n, int a, int b, int c) throws InterruptedException
//Move top n disk from tower 'a' to tower 'c'
//tower 'b' used for swapping
{
if(n>=1)
 {
 moveTopN(g,n-1,a,c,b);
 drawStill(g);
 Thread.sleep(700);
 from=a;
 to=c;
 //animating the move
 animator(g);
 moveTopN(g,n-1,b,a,c);
 }
}

public static void main(String[] args)
{

int i;
String s=JOptionPane.showInputDialog("Enter number of disks");
n=Integer.parseInt(s);
HanoiAnimated ha=new HanoiAnimated();
//setting all tower empty
for(i=0;i<3;i++)
 top[i]=-1;

//putting all disks on tower 'a'
for(i=n;i>0;i--)
 {
 push(1,i);
 }

JFrame fr=new JFrame();
fr.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
fr.setLayout(new BorderLayout());
fr.setSize(640,360);
fr.add(ha);
ha.setSize(fr.getSize());
fr.setVisible(true);
l=ha.getWidth()/4;
b=ha.getHeight()-50;
u=b-n*12;
//start solving
try{
ha.moveTopN(ha.getGraphics(),n,1,2,3);
}catch(Exception ex){}
}

}

Java Program to Solve Tower of Hanoi Puzzle Problem

This is a java program to solve towers of hanoi puzzle problem. This simple java program gives solution for tower of hanoi problem with any number of disks. Tower of Hanoi is a mathematical game or puzzle. It is also called tower of brahma or Lucas' tower. There are three towers (or rods) and a number of disks of different diameters. Initially, The disks have hole at center so that it can slide on to the rods. Initially all disks are stacked on the first tower, say tower A, such that no disk is placed over a smaller disk. The goal or objective is to move all these disks from tower A (first tower) to tower C (third tower). But you should obey the following rules. The rules of towers of hanoi puzzle are:

Java Program to Find Power of a Number

This is a java program to calculate power of a given number. The inputs are the number and its exponent (power). For example, if you give m and n, the result is m^n. You may use built-in function Math.pow() or hard code it.

Using Built-in Function

import java.util.Scanner;

public class Power{

public static void main(String[] args)
{
int m,n;
Scanner sc=new Scanner(System.in);
System.out.println("Enter number and its power");
m=sc.nextInt();
n=sc.nextInt();
System.out.printf("m^n = %.0f",(float)Math.pow(m,n));
}
}

Without using Built-in function

import java.util.Scanner;

public class Power{

public static void main(String[] args)
{
int m,n,i,p=1;
Scanner sc=new Scanner(System.in);
System.out.println("Enter number and its power");
m=sc.nextInt();
n=sc.nextInt();
for(i=0;i<n;i++)
    p*=m;
System.out.printf("m^n = %d",p);
}
}

Java Program For Matrix Multiplication

This is a java program for Matrix Multiplication. To understand how it works, you should first know how matrix multiplication is done mathematically.

import java.util.Scanner;

public class MatrixMult{

public static void main(String[] args)
{
int[][] m1=new int[10][10];
int[][] m2=new int[10][10];
int[][] prod=new int[10][10];
int i,j,k,r1,c1,r2,c2;
Scanner sc=new Scanner(System.in);
System.out.println("Enter number of rows and columns of first matrix:");
r1=sc.nextInt();
c1=sc.nextInt();
System.out.println("Enter number of rows and columns of second matrix:");
r2=sc.nextInt();
c2=sc.nextInt();
if(r2==c1)
    {
    System.out.println("Enter elements of First matrix (row wise):");
    for(i=0;i<r1;i++)
        for(j=0;j<c1;j++)
            m1[i][j]=sc.nextInt();
    System.out.println("Matrix1 is :");
    for(i=0;i<r1;i++)
        {
        for(j=0;j<c1;j++)
            System.out.printf("%d ",m1[i][j]);
        System.out.printf("\n");
        }
    System.out.println("Enter elements of Second matrix (row wise):");
    for(i=0;i<r2;i++)
        for(j=0;j<c2;j++)
            m2[i][j]=sc.nextInt();
    System.out.println("Matrix2 is:");
    for(i=0;i<r2;i++)
        {
        for(j=0;j<c2;j++)
            System.out.printf("%d ",m2[i][j]);
        System.out.printf("\n");
        }
    System.out.println("Product of the Matrices (M1 x M2):");
    for(i=0;i<r1;i++)
        {
        for(j=0;j<c2;j++)
            {
            prod[i][j]=0;
            for(k=0;k<r1;k++)
                prod[i][j]+=m1[i][k]*m2[k][j];
            System.out.printf("%d ",prod[i][j]);
            }
        System.out.print("\n");
        }
    }
else
    {
    System.out.println("Matrices can't be multiplied.");
    System.out.print("No. of columns of first matrix and no of rows of second are different.");
    }
}
}

Output

Enter number of rows and columns of first matrix:
2
2
Enter number of rows and columns of second matrix:
2
2
Enter elements of First matrix (row wise):
5
8
6
4
Matrix1 is :
5 8 
6 4 
Enter elements of Second matrix (row wise):
5
6
8
9
Matrix2 is:
5 6 
8 9 
Product of the Matrices (M1 x M2):
89 102 
62 72 

Java Program to Display Multiplication Tables of Given Number

This is a java program to display multiplication table of given number. For java program to display multiplication table of all numbers from 1 to 10, see this post: Program to display multiplication table of all numbers from 1 to 10

import java.util.Scanner;

public class Multiples{

public static void main(String[] args)
{
    int n, i;
    Scanner sc=new Scanner(System.in);
    System.out.printf("Enter the number:");
    n=sc.nextInt();
    for(i=1; i<=10; ++i)
        System.out.printf("%d * %d = %d \n", i, n, n*i);
}
}

Output:

Enter the number:5
1 * 5 = 5
2 * 5 = 10
3 * 5 = 15
4 * 5 = 20
5 * 5 = 25
6 * 5 = 30
7 * 5 = 35
8 * 5 = 40
9 * 5 = 45
10 * 5 = 50

Java Program to Display Multiplication Tables of All Number from 1 to 10

This is  a java program to display multiplication tables of all number from 1 to 10. To see java program to display multiplication table of given number only, see this program:
Program to Display Multiplication Table of Given Number

public class Multiples{

public static void main(String[] args)
{
int i,j;
for(i=1;i<=10;i++)
    {
    for(j=1;j<=10;j++)
        System.out.printf("%d*%d=%d  ",i,j,i*j);
    System.out.printf("\n");
    }
}

}

Output:

1*1= 1 1*2= 2 1*3= 3 1*4= 4 1*5= 5 1*6= 6 1*7= 7 1*8= 8 1*9= 9 1*10=10
2*1= 2 2*2= 4 2*3= 6 2*4= 8 2*5=10 2*6=12 2*7=14 2*8=16 2*9=18 2*10=20
3*1= 3 3*2= 6 3*3= 9 3*4=12 3*5=15 3*6=18 3*7=21 3*8=24 3*9=27 3*10=30
4*1= 4 4*2= 8 4*3=12 4*4=16 4*5=20 4*6=24 4*7=28 4*8=32 4*9=36 4*10=40
5*1= 5 5*2=10 5*3=15 5*4=20 5*5=25 5*6=30 5*7=35 5*8=40 5*9=45 5*10=50
6*1= 6 6*2=12 6*3=18 6*4=24 6*5=30 6*6=36 6*7=42 6*8=48 6*9=54 6*10=60
7*1= 7 7*2=14 7*3=21 7*4=28 7*5=35 7*6=42 7*7=49 7*8=56 7*9=63 7*10=70
8*1= 8 8*2=16 8*3=24 8*4=32 8*5=40 8*6=48 8*7=56 8*8=64 8*9=72 8*10=80
9*1= 9 9*2=18 9*3=27 9*4=36 9*5=45 9*6=54 9*7=63 9*8=72 9*9=81 9*10=90
10*1=10 10*2=20 10*3=30 10*4=40 10*5=50 10*6=60 10*7=70 10*8=80 10*9=90 10*10=100

Java Program to Rotate Polygon - 2d Transformation Rotation in Java

This is a java program for rotation transformation in computer graphics. Rotation is one of the important 2d transformations in computer graphics. The program will tell you how to rotate points or polygon around a point (the pivot point). This CG lab program in java language reads the number of sides of polygon, co-ordinates of its vertices, the pivot point for rotation, and angle of rotation. It displays the original polygon and translated polygon in different colors in same screen. This program will tell you how to rotate a polygon in java. I override the paintComponent() method of JPanel to draw on a JPanel.

Java Program for Engine Piston Movement Animation

This program simulates the motion of the components of a two stroke engine. It shows the movement of piston, connecting rod and crank by animating them in java. The program override the paint method of a JFrame to simulate the piston movement in two stroke engine. This can be computer graphics lab (CG lab) problem. The program is as given below. The program uses sin and cos functions to simulate the crank. Also it uses the equation to find the distance between to points.

Decimal to BCD Converter in Java

In this post,we will see java program to convert decimal number to BCD representation. Binary-coded decimal (BCD) is a class of binary encodings of decimal numbers where each decimal digit is represented by a fixed number of bits, usually four. Thus the decimal digit 1 corresponds to  0001, 2 corresponds to 0010,....  8 corresponds to 1000 and 9 corresponds to 1001. Therefore, decimal number 194 can be represented in BCD as 0001 1001 0100. It should be noted that 1010, 1011, 1100, 1101,1110 and 1111 are illegal in BCD. The following java program converts any decimal number to BCD. But in this program, for conversion each digit in the decimal, we use Integer.toBinaryString() method. So, i have added another program which does not use this method.

Program 1:

    public static String toBCD(int num)
    {
        String BCD="";
        while(num!=0)
        {
        int t=num%10;
        String tBCD=Integer.toBinaryString(t);
        while(tBCD.length()<4)
            {
            tBCD="0"+tBCD;
            }
        BCD=tBCD+BCD;
        num/=10;
        }
        return BCD;
    }

Program 2:

import java.util.Scanner;
public class DecimalToBCD {

static String digitToBcd(int digit)
{
    String str="";
    for(int i=3;i>=0;i--)
        {
        int d=(int) Math.pow(2,i);
        if(digit/d!=0)
            {
                str+="1";
                digit-=d;
            }
        else
            str+="0";
        }
    return str;
}
    
    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        int decimal=sc.nextInt();
        int digit;
        String BCD="";
        while(decimal!=0)
            {
            digit=decimal%10;
            BCD=digitToBcd(digit)+" "+BCD;
            decimal/=10;
            }
        System.out.println("BCD is:"+BCD);
        
    }
}

The second program does not use any built in methods for conversion of decimal to BCD.

Java Program to Simulate Motion of Simple Pendulum

This is a java program to simulate motion of simple pendulum using java graphics. This was a problem given in computer graphics lab, which i was supposed to do using graphics.h header file in C. This is the java version of the same. If you are looking for a C Program, here it is: C Program to Simulate Simple Pendulum Motion - Computer Graphics Lab.

Output is as follows:

import java.awt.Color;
import java.awt.Graphics;
import javax.swing.JFrame;


public class JavaApplication1 extends JFrame{

    int pivotx,pivoty;
    double thetamax,theta;;
    double len=260;
    int x,y,ymax,xmax;
    int bobradius=30;
    int xsign=-1,ysign=1;
    double omega;
    
    public JavaApplication1()
    {
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setSize(600,400);
        thetamax=60*Math.PI/180;
        pivotx=getWidth()/2;
        pivoty=40;
        ymax=(int) (pivoty+len*Math.cos(thetamax));
        xmax=(int) (pivotx+len*Math.sin(thetamax));
        x=xmax;
        y=ymax;
        theta=thetamax;
        System.out.println("pivotx:"+pivotx+" pivoty:"+pivoty);
        System.out.println("starting x:"+x+ "y:"+y);
        System.out.println("starting theta="+theta);
        t.start();
    }

    @Override
    public void paint(Graphics g) {
        System.out.println("called");        
        g.setColor(Color.WHITE);
        g.fillRect(0, 0,getWidth(),getHeight());
        g.setColor(Color.red);
        g.fillOval(pivotx-4,pivoty-4,8,8);
        g.drawLine(pivotx,pivoty, x,y);
        g.fillOval(x-bobradius/2,y-bobradius/2,bobradius,bobradius);
        
    }
    
    Thread t=new Thread()
    {
      public void run()
      {
    try {
      while(true)
      {
      if(x>=pivotx+Math.abs(len*Math.sin(thetamax)))
        {
        System.out.println("right extreme");
        xsign=-1;
        ysign*=-1;
        x=xmax-1;
        Thread.sleep(40);
        }
      else if(x<=pivotx-Math.abs(len*Math.sin(thetamax)))
      {
          System.out.println("left extreme");
          ysign*=-1;
          xsign=1;
          x=(int) (pivotx-Math.abs(len*Math.sin(thetamax))+2);
          Thread.sleep(40);
      }
      else if(y>=pivoty+len)
        {
              ysign*=-1;
              System.out.println("mean position");
        }

      omega=y/60*Math.PI/180;
      double decr=xsign*omega;
          System.out.println("decrement:"+decr);
      theta=theta+decr;
      x=(int) (pivotx+len*Math.sin(theta));
      y=(int) (pivoty+len*Math.cos(theta));
          System.out.println("new theta:"+theta);
      repaint();
      Thread.sleep(40);
    
      }
            } catch (InterruptedException ex) {}
      }
    };
    
    
    public static void main(String[] args) {
        new JavaApplication1().setVisible(true);
    }
    
}

Simplest UDP Chat Program to Run on Single Computer in Java

This is a very simple UDP chat program using java with GUI (Graphical User Interface). The program uses DatagramPackets to send messages over network. Remember, this program only to be run on a single computer (for network simulation purpose). If you want a real UDP program that works on any network, see this post: Chat Room Application using UDP in Java
Program explanation is given below the program.

import java.io.*;
import javax.swing.*;
import java.net.*;
import java.awt.event.*;
import java.util.*;

public class UDPChat extends JFrame implements ActionListener
{
DatagramSocket ds;
JTextField txt;
JButton send;
JTextArea msgs;
int myport;
int destport;
DatagramPacket p;
byte[] b=new byte[200];

public UDPChat()
{
try{
try{
ds=new DatagramSocket(9999);
myport=9999;
p=new DatagramPacket(b,200);
ds.receive(p);
destport=p.getPort();
}catch(Exception ex)
{
ds=new DatagramSocket(0);
myport=ds.getLocalPort();
destport=9999;
String msg="hi";
p=new DatagramPacket(msg.getBytes(),msg.length(),InetAddress.getLocalHost(),destport);
ds.send(p);
}
setLayout(null);
txt=new JTextField();
send=new JButton("Send");
msgs=new JTextArea();
setSize(300,600);
add(txt);
txt.setSize(220,25);
txt.setLocation(5,5);
add(send);
send.setSize(70,25);
send.setLocation(230,5);
add(msgs);
msgs.setSize(300,530);
msgs.setLocation(0,70);
send.addActionListener(this);
receive.start();
}catch(Exception ex){ex.printStackTrace();}
}

public void actionPerformed(ActionEvent ae)
{
try{
DatagramPacket pkt=new DatagramPacket(txt.getText().getBytes(),txt.getText().length(),InetAddress.getLocalHost(),destport);
ds.send(pkt);
}catch(Exception e){e.printStackTrace();}
txt.setText("");
}

Thread receive=new Thread()
{
public void run()
{
try{
while(true)
 {
 DatagramPacket dp=new DatagramPacket(b,200);
 ds.receive(dp);
 msgs.setText(msgs.getText()+"\n"+new String(b));
 }
}catch(Exception exx){exx.printStackTrace();}
}
};

public static void main(String[] args)
{
UDPChat s=new UDPChat();
s.setVisible(true);
}

}

This simple program is enough to run as server or client. When the first user runs the application, it opens a DatagramSocket with port number 9999 (see line 22 in code). Since no Exception will be thrown from this line, it sets myport as 9999. Then waits to receive a DatagramPacket from the other user. When the packet is received, it takes destport from the received packet. Then starts adding GUI elements and then starts the thread to receive messages.

But when the second instance (client) of the program is run, line 22 in code throws a SocketException. Thus execution goes to the catch block. There it opens a DatagramSocket at some random port (ephemeral port assigned by OS). Then, sends a packet to port 9999 in the same PC. This time the first instance (server) is still waiting for a packet as said earlier. It receives this DatagramPacket sent by client a gets its destination port. The client's destport is 9999, as it knew it is already occupied by the SocketException.

The sending of message is carried out when send button is clicked. We use an ActionListener for that. The method public void actionPerformed(ActionEvent ae) is invoked whenever the button is clicked.