Tutorials, tips and tricks about java programming language. Answers for many doubts about java programming language. Answering many howtos. Sample java projects and source code, java games, java programs for java practical labs.
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
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) {}
}
}
};
}
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.
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.
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.
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:
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.
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){}
}
}
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:
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);
}
}
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
