java's setColor results in illegal argument exception or assertions are skipped

Question

I have this code (which is called from paintComponent in a class that inherits from JPanel.

    assert(red >= 0);
    assert(red <= 255);
    assert(green >= 0);
    assert(green <= 255);
    assert(blue >= 0);
    assert(blue <= 255);
    Color color = new Color(red, green, blue);

After some time I get an exception:

Exception in thread "AWT-EventQueue-0" java.lang.IllegalArgumentException: Color parameter outside of expected range: Red
    at java.awt.Color.testColorValueRange(Unknown Source)
    at java.awt.Color.<init>(Unknown Source)
    at java.awt.Color.<init>(Unknown Source)
    at display.DrawCanvas.drawLed(DrawCanvas.java:55)
    at display.DrawCanvas.paintComponent(DrawCanvas.java:36)
    at javax.swing.JComponent.paint(Unknown Source)

DrawCanvas.java:55 (line 55) is the last line in the code fragment above.

How is it possible that an argument is out of range while all values are between 0 and 255 (included)?

Are assertions enabled? What is the `red` value? Are any of `red`, `green`, or `blue` `float`? — rgettman, Mar 26 '19 at 22:21
I just checked indeed (I couldn't set a breakpoint but added extra code), and red has value 267 ... now checking how to enable assertions. — Michel Keijzers, Mar 26 '19 at 22:22
[What does the Java assert keyword do, and when should it be used?](https://stackoverflow.com/q/2758224/5221149) TL;DR: Don't use `assert` — Andreas, Mar 26 '19 at 22:39

score 1 · Accepted Answer · answered Mar 26 '19 at 22:38

Java assertions aren't enabled by default.

From the command line, pass the -ea command line flag to enable assertions.
```
java -ea your.main.ClassHere
```
From Eclipse, you'll have to go to your particular Run Configuration and add in -ea in your "VM Arguments" as described here.
From IntelliJ, it's similar. In your particular Run Configuration, add in -ea in "VM options".

Regardless of your IDE, the goal is to get it to add -ea after java and before your main class name to enable assertions.

Once you've got assertions enabled, then they will stop your program with an AssertionError before you get the IllegalArgumentException.

This particular case will work since you've indicated in comments that the value is an int -- 267. Note that if you happen to have float values, then they could pass the assertions with invalid values that are greater than 1.0f and less than or equal to 255.0f.

java's setColor results in illegal argument exception or assertions are skipped

1 Answers1