Collsion detection in java Applet ,obstacle as well as player are moving

Question

sir/Ma'am Sorry for the silly question ,as I am a novice please help me to detect collision between the oval obstacles moving with the help of threads and the player a rectangle is moving with the help of Arrow keys(Keylistener used). this is the code

public void init()
{
    r = new Rectangle(0, 0, 50, 20);
    addKeyListener(this);
    Collision();

}
public void Collision()
    {
        if((r.x==x_pos) || (r.y==y_pos))
        System.exit(0);
    }

    public void paint (Graphics g)
{   
    g.drawString("first click the left button of mouse keeping it over the rectangle then move the rectangle by arrow keys",20,10);

    g.fillRect(r.x, r.y, r.width, r.height);
    g.setColor  (Color.red);
    g.fillOval (x_pos , 10 , 2*radius, 2*radius);
    g.setColor  (Color.black);
    g.fillOval (10 ,  y_pos , 4*radius, 1*radius);
    g.setColor  (Color.pink);
    g.fillOval (x_pos , 40 , 2*radius, 2*radius);
    g.setColor  (Color.yellow);
    g.fillOval (x_pos ,  120 , 4*radius, 2*radius);
    g.setColor  (Color.gray);
    g.fillOval (120 , y_pos , 2*radius, 1*radius);
    g.setColor  (Color.orange);
    g.fillOval (x_pos , 150, 2*radius, 2*radius);
    g.setColor  (Color.magenta);
    g.fillOval (x_pos, 260 , 3*radius, 2*radius);
    g.setColor  (Color.cyan);
    g.fillOval (240 , y_pos , 2*radius, 2*radius);
    g.setColor  (Color.green);
    g.fillOval (280 , y_pos , 2*radius, 2*radius);
    g.setColor  (Color.blue);
    g.fillOval (x_pos , 290 , 2*radius, 2*radius);
    g.setColor  (Color.orange);
    g.fillOval (x_pos , y_pos , 2*radius, 2*radius);
    g.setColor  (Color.magenta);
    g.fillOval (x_pos ,  360 , 2*radius, 2*radius);
    g.setColor  (Color.darkGray);
    g.fillOval (x_pos , 390 , 2*radius, 2*radius);

}


public void start ()
{

    Thread th1 = new Thread (this);
    th1.start ();

}

              public void stop()
{

}

public void destroy()
{

}

public void run ()
{

    while(true)
    {

        x_pos++;
        try
        {
            Thread.sleep(10);
        }
        catch(InterruptedException e){}
        if(x_pos++> getSize().width)
        x_pos=0;
        repaint();

        y_pos++;
        try
        {
            Thread.sleep(10);
        }
        catch(InterruptedException e){}
        if(y_pos++> getSize().height)
        y_pos=0;
        repaint();

    }
    }


    public void keyPressed(KeyEvent e)
    {
         int keyCode = e.getKeyCode();

         if(keyCode == KeyEvent.VK_LEFT)
        {
             r.x -= 10;
            if(r.x < 0) 
            r.x = 0;
             repaint();
         }
         else if(keyCode == KeyEvent.VK_RIGHT)
        {
            r.x += 10;
             if(r.x > getSize().width-r.width)
             {
                 r.x = getSize().width-r.width;
             }
            repaint();
        }
        else if(keyCode == KeyEvent.VK_UP)
         {
             r.y -= 10;
             if(r.y < 0) r.y = 0;
            repaint();
        }
        else if(keyCode == KeyEvent.VK_DOWN)
        {
             r.y += 10;
            if(r.y > getSize().height-r.height)
            {
                 r.y = getSize().height-r.height;
             }
            repaint();
        }

    }   
        public void keyReleased(KeyEvent e){}
         public void keyTyped(KeyEvent e){}

}

Answer 1

Here is the code for a basic ping pong game maybe it will help in solving your problem....

package com.piyush;

import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.KeyEvent;

import javax.swing.JPanel;

public class GamePanel extends JPanel implements Runnable{

boolean player1Flag1,player1Flag2, player2Flag1, player2Flag2;
boolean flag,gameOver;
private int ballX = 10, ballY = 100, player1X=10, player1Y=100, player2X=230, player2Y=100;
int scorePlayer1=0, scorePlayer2=0;
int right=5; // to the right
int left= -5; //to the left
int up=5; // upward
int down= -5; // down
int width, height; // Width and height of the ball

Thread t;

public GamePanel() {
    super();
    flag=true;
    this.setBackground(Color.GRAY);
    t=new Thread(this);
    t.start();
    // TODO Auto-generated constructor stub
}
public void keyPressed(KeyEvent evt)
{
    switch(evt.getKeyCode())
    {

        case KeyEvent.VK_W :
            player1Flag1 = true;
            break;
        case KeyEvent.VK_S : 
            player1Flag2 = true;
            break;


        case KeyEvent.VK_UP:
            player2Flag1=true;
            break;
       case KeyEvent.VK_DOWN:
           player2Flag2=true;
            break;
    }

}
public void keyReleased(KeyEvent evt)
{
    switch(evt.getKeyCode())
    {

        case KeyEvent.VK_W :
            player1Flag1 = false;
            break;
        case KeyEvent.VK_S : 
            player1Flag2 = false;
            break;


        case KeyEvent.VK_UP:
            player2Flag1=false;
            break;
       case KeyEvent.VK_DOWN:
           player2Flag2=false;
            break;
    }

}

public void paintComponent(Graphics gc){

    super.paintComponent(gc);


    gc.setColor(Color.black);
    gc.fillOval(ballX, ballY, 8,8);


    gc.fillRect(player1X, player1Y, 10, 25);
    gc.fillRect(player2X, player2Y, 10, 25);


    gc.drawString("Player1: "+scorePlayer1, 25, 10);
    gc.drawString("Player2: "+scorePlayer2, 150, 10);

    if(gameOver)
        gc.drawString("Game Over", 100, 125);
}


public void positionBall(int nx, int ny)
{
    ballX= nx; 
    ballY= ny; 
    this.width=this.getWidth();
    this.height=this.getHeight();
    repaint();
}
 public void moverPlayer1()
    {
        if (player1Flag1 == true && player1Y >= 0)
            player1Y += down;
        if (player1Flag2 == true && player1Y <= (this.getHeight()-25))
            player1Y += up;
        positionPlayer1(player1X, player1Y);
    }


    public void moverPlayer2()
    {
        if (player2Flag1 == true && player2Y >= 0)
            player2Y += down;
        if (player2Flag2 == true && player2Y <= (this.getHeight()-25))
            player2Y += up;
        positionPlayer2(player2X, player2Y);
    }


    public void positionPlayer1(int x, int y){
        this.player1X=x;
        this.player1Y=y;
        repaint();
    }

    public void positionPlayer2(int x, int y){
        this.player2X=x;
        this.player2Y=y;
        repaint();
    }

@Override
public void run() {
    boolean rToL=false;
    boolean dToU=false;

    while(true){

        if(flag){

        if (rToL) 
        {

            ballX += right;
            if (ballX >= (width - 8))
                rToL= false;
        }
        else
        {

            ballX += left;
            if ( ballX <= 0)
                rToL =  true;
        }



        if (dToU) 
        {

            ballY += up;
            if (ballY >= (height - 8))
                dToU= false;

        }
        else
        {

            ballY += down;
            if ( ballY <= 0)
                dToU =  true;
        }
       positionBall(ballX, ballY);


        try 
        {
            Thread.sleep(50);
        }
        catch(InterruptedException ex)
        {

        }


        moverPlayer1();


        moverPlayer2();


        if (ballX >= (width - 8))
            scorePlayer1++;


        if ( ballX == 0)
            scorePlayer2++;


        if(scorePlayer1==5 || scorePlayer2==5){
            flag=false;
            gameOver=true;
        }


        if(ballX==player1X+10 && ballY>=player1Y && ballY<=(player1Y+25))
            rToL=true;


        if(ballX==(player2X-5) && ballY>=player2Y && ballY<=(player2Y+25))
            rToL=false;
        }
    }

}

}

And the test class as follows:

package com.piyush;

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Rectangle;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

    public class Test extends JFrame{


private JPanel jContentPane = null;

private GamePanel panel = null; 

private GamePanel getPanel() {
    if (panel == null) {
        panel = new GamePanel(); 
    }
    return panel;
}

/**
 * This is the default constructor
 */
public Test() {
    super();
    initialize();
          this.addKeyListener(new KeyAdapter() {

        public void keyPressed(KeyEvent evt) {
            formKeyPressed(evt);
        }

        public void keyReleased(KeyEvent evt) {
            formKeyReleased(evt);
        }
    });

}


private void formKeyPressed(KeyEvent evt)
{
    panel.keyPressed(evt);
}

private void formKeyReleased(KeyEvent evt)
{
    panel.keyReleased(evt);
}


private void initialize() {
    this.setResizable(false);
    this.setBounds(new Rectangle(312, 184, 250, 250)); 
    this.setMinimumSize(new Dimension(250, 250));
    this.setMaximumSize(new Dimension(250, 250));
    this.setBackground(Color.gray);     
    this.setContentPane(getJContentPane());
    this.setTitle("Pong");
}

/**
 * This method initializes jContentPane
 * 
 * @return javax.swing.JPanel
 */
private JPanel getJContentPane() {
    if (jContentPane == null) {
        jContentPane = new JPanel();
        jContentPane.setLayout(new BorderLayout());
        jContentPane.add(getPanel(), BorderLayout.CENTER);
        jContentPane.setBackground(Color.gray);
    }
    return jContentPane;
}

public static void main(String[] args) {
    // TODO Auto-generated method stub
    SwingUtilities.invokeLater(new Runnable() {
        public void run() {
            Test m = new Test();
            m.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            m.setVisible(true);
        }
    });
}

}

Let me know if you can't understand any part.