{JAVA} Rectangle collision detection

**Hi guys,i have 2 questions.

1. why "Hit" word do not appear.
2. what type of code i need to add to make these 2 rects collide and bounce each other based on my code.Just give me a hint . i'll do it myself.
   Below is the code for question 1.
   Thank you.**

///////////////////////////////////////////////////////

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;
import java.awt.Graphics;
import java.awt.Color;
import java.awt.Rectangle;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
           
public class f5 extends JPanel implements ActionListener {
               
static JFrame frame;
static Timer t;
static int x, velx, x2, velx2;
           
f5() {
               
t = new Timer(5, this);
x = 100;
x2 = 400;
velx = 2;
velx2 = 2;
               
               
       frame = new JFrame();
               
       frame.setSize(500, 400);
       frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
       frame.setVisible(true);
       frame.add(this);
            
}
            
public void paintComponent(Graphics g) {
        super.paintComponent(g);
               
        Rectangle r1 = new Rectangle();
        Rectangle r2 = new Rectangle();
               
        g.setColor(Color.BLUE);
        g.fillRect(x, 10, 50, 30);
          
        g.setColor(Color.RED);
        g.fillRect(x2, 10, 50, 30);
           
     if(r1.intersects(r2)){
            g.drawString("HIT!!!!!", 250, 200);
         }

                t.start();
            }    
           
public void actionPerformed(ActionEvent e) {
            
            if(x < 0 || x > 450) {
                    velx = -velx;
                }
            if(x2 < 0 || x2 > 450) {
                    velx2 = -velx2;
                }
             
             x -= velx;
             x2 += velx2;
           
                 
                  repaint();
            }
           
public static void main(String args[]){
      new f5();
            }
             }

1. The coordinates of rectangles are not defined right now, so they won't intersect (the comparison always return false). You are just creating r1 and r2 without defining anything. You should initialize them using constructor new Rectangle(int x, int y, int width, int height).

2. One way is you can create a class field to store the coordinate of the rectangle, repeatedly check their coordinate to see whether they collide.

Did you not read the javadoc for the no-arg constructor of class Rectangle?
> Constructs a new Rectangle whose upper-left corner is at (0, 0) in the coordinate space, and whose width and height are both zero.

This means that r1 and r2 have zero size and hence they cannot intersect. You need to give r1 and r2 dimensions when you create them. Note that method fillRect(), in class java.awt.Graphics, simply paints a region of the screen. It has nothing to do with r1 and r2. So you should change these two lines in method paintComponent()

Rectangle r1 = new Rectangle();
Rectangle r2 = new Rectangle();

to this:

Rectangle r1 = new Rectangle(x, 10, 50, 30);
Rectangle r2 = new Rectangle(x2, 10, 50, 30);

Then they will intersect.

Regarding your second question. You need to check, in method actionPerformed(), whether the rectangles r1 and r2 intersect and if they do, you need to reverse the direction of movement – exactly as you do when one of the rectangles reaches the edge of the JPanel. In order to do that, you could make r1 and r2 members of class f5.

The below code shows how to achieve both your requests, i.e. determine when the rectangles intersect and have them "bounce" of each other when they do intersect.

You only require one instance of the Timer, so you should not create a new one each time in method paintComponent(). You can create it once, in the constructor of class f5.

Note that the members of class f5 should be instance members and not static members. Also note that according to java naming conventions, the name of the class should be F5.

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;
import java.awt.Graphics;
import java.awt.Color;
import java.awt.Rectangle;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
           
public class F5 extends JPanel implements ActionListener {
    private JFrame frame;
    private Timer t;
    private int x, velx, x2, velx2;
    private Rectangle r1;
    private Rectangle r2;

    F5() {
        t = new Timer(5, this);
        x = 100;
        x2 = 400;
        r1 = new Rectangle(x, 10, 50, 30);
        r2 = new Rectangle(x2, 10, 50, 30);
        velx = 2;
        velx2 = 2;
        frame = new JFrame();
        frame.setSize(500, 400);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.add(this);
        frame.setVisible(true);
        t.start();
    }

    public void paintComponent(Graphics g) {
        super.paintComponent(g);

        r1 = new Rectangle(x, 10, 50, 30);
        r2 = new Rectangle(x2, 10, 50, 30);

        g.setColor(Color.BLUE);
        g.fillRect(x, 10, 50, 30);

        g.setColor(Color.RED);
        g.fillRect(x2, 10, 50, 30);
    }

    public void actionPerformed(ActionEvent e) {
        if (x < 0 || x > 450 || r1.intersects(r2)) {
            velx = -velx;
        }
        if (x2 < 0 || x2 > 450 || r1.intersects(r2)) {
            velx2 = -velx2;
        }

        x -= velx;
        x2 += velx2;

        repaint();
    }

    public static void main(String args[]) {
        new F5();
    }
}