How to generate random colors in Java?

Question

I would like to generate a random color for JLabel in Java. The JLabel will be changing the background every 100 ms and the background has to be random. How to do this?

I thought of using javax.swing.Timer class to do this. See, i am stumped.I am not even getting a background when i have tried the label.setBackground(Color.CYAN)

JLabel l=new JLabel("Label");
Timer t=new Timer(2,new ActionListener(){
  public void actionPerformed(ActionEvent ae)
  {
       // what is the code here?
  }
});

What were the search terms? I suggest SO for '[java] color random'. — Andrew Thompson, Jul 17 '13 at 10:14

score 11 · Answer 1 · answered Jul 17 '13 at 10:17

11

If I were, I would only randomize the hue component, not the brightness, not the saturation.

double hue = Math.random();
int rgb = Color.HSBtoRGB(hue,0.5,0.5);
Color color = new Color(rgb);

It will be much more pretty.

answered Jul 17 '13 at 10:17

David

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JavaTechnical · Accepted Answer · 2013-07-17T10:30:14.123

6

You can use java.util.Random class and the constructor,

I am not even getting a background when i have tried the label.setBackground(Color.CYAN)

This is because the label is not opaque. Make it opaque for the background to be visible.

final JLabel label=new JLabel("Label");
        // Label must be opaque to display
        // the background
        label.setOpaque(true);

        final Random r=new Random();
        Timer t=new Timer(100,new ActionListener(){
            public void actionPerformed(ActionEvent ae)
            {
                Color c=new Color(r.nextInt(256),r.nextInt(256),r.nextInt(256),r.nextInt(256));
                label.setBackground(c);
            }
        });
        t.start();

You can use any of the constructors in the the Color class. For generating float values you can use Math.random() or r.nextFloat()

edited Jul 17 '13 at 10:30

answered Jul 17 '13 at 10:08

JavaTechnical

8,846
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It is not compiling! :( – Say Off Jul 17 '13 at 10:24
Why? What is the error? – JavaTechnical Jul 17 '13 at 10:24
I am getting reference to Timer is ambiguous – Say Off Jul 17 '13 at 10:25
4

Import the correct `Timer` ! – AllTooSir Jul 17 '13 at 10:26
3

Both `java.util` and `javax.swing` contain Timer class, for using `Random` class just write `import java.util.Random;` it has to work. – JavaTechnical Jul 17 '13 at 10:26
@SayOff Just to be clear, the correct `Timer` to import is `javax.swing.Timer`. – afsantos Jul 17 '13 at 10:32
1

@JavaTechnical Just wanted to point out, for correctness, that you should replace `255` with `256`, since `nextInt()` returns a *«value between 0 (inclusive) and the specified value (exclusive)»*. `Color` accepts integers from 0 to 255 inclusive. – afsantos Jul 17 '13 at 10:34
1

I replaced it before you have commented! First :)! Thanks anyways! +1 – JavaTechnical Jul 17 '13 at 10:36

How to generate random colors in Java?

2 Answers2