Java Applet更改为Paint

Question

I have an applet that's only purpose is to create a box and each time it's painted it changes color. Right now it is not changing color at all, it simply creates a random background color to start and sticks with it whenever painted but I need it to change. Any help on what I'm doing wrong would be appreciated.

import java.applet.*;
import java.awt.*;
import java.util.*;

public class AppletSubClass2 extends Applet {
public void init() {
    System.err.println("Hello from AnAppletSubClass.init");
    setBackground(color);
}
public void paint(Graphics g) {
    System.err.println("Hello from .paint!This time the applet will change colors when painted");
    setBackground(new Color(randomNum1, randomNum2, randomNum3));
}
Random rand = new Random();
int randomNum1 = rand.nextInt(251);
int randomNum2 = rand.nextInt(251);
int randomNum3 = rand.nextInt(251);
Color color = new Color(randomNum1, randomNum2, randomNum3);
}

Answer 1

try this, for me is working:

    setBackground(new Color(rand.nextInt(251), rand.nextInt(251), rand.nextInt(251)));

your applet not change color, because define a random color in the begining, and each time it paint repaint with the same random color declared in the begin.

i hope this help you

Answer 2

You've basically broken the paint chain, nothing is actually painting your background color...

You could do something like...

public void paint(Graphics g) {
    int randomNum1 = rand.nextInt(251);
    int randomNum2 = rand.nextInt(251);
    int randomNum3 = rand.nextInt(251);
    Color color = new Color(randomNum1, randomNum2, randomNum3);
    setBackground(color);
    super.paint(g);
}

But this will set up a infinite cycle of repaint requests which will eventually consume your CPU cycles and make you PC unusable (not to mention flicker like crazy)...

A better solution might be to override the getBackgroundColor method...

@Override
public Color getBackground() {
    int randomNum1 = rand.nextInt(251);
    int randomNum2 = rand.nextInt(251);
    int randomNum3 = rand.nextInt(251);
    Color color = new Color(randomNum1, randomNum2, randomNum3);
    return color;
}

This will mean that each time this method is called, it will generate a random color. You can then use, some other process, to force the applet to repaint...

Answer 3

This part of your code only runs once, when you AppletSubClass2 object is instantiated.

Random rand = new Random();
int randomNum1 = rand.nextInt(251);
int randomNum2 = rand.nextInt(251);
int randomNum3 = rand.nextInt(251);
Color color = new Color(randomNum1, randomNum2, randomNum3);

So every call to repaint() after that will use the same values of randomNum1, randomNum2, and randomNum3.

What you probably want is a way to generate a random color, in a method:

public Color generateRandomColor() {
    Random rand = new Random();
    int randomNum1 = rand.nextInt(251);
    int randomNum2 = rand.nextInt(251);
    int randomNum3 = rand.nextInt(251);
    return new Color(randomNum1, randomNum2, randomNum3);
}

Then use that in repaint():

public void paint(Graphics g) {
    setBackground(generateRandomColor());
}