Weird Java errors

Sometimes the error messages the Java compiler gives aren't entirely self-explanatory. This is a list of some error messages, with a description of what it probably means. If you discover a new error message that doesn't make sense, contact me; we'll find the solution and put a description here too.

Can't find class ``x''

Go to Project Settings under the Edit menu, and select Java Project. The text in the ``Main Class'' field should contain the name of the class you're using. (If you're editing Prime.java, the class is Prime; if you're editing AddBigNumbers.java, the class is AddBigNumbers.)

Could not create output file (possibly you're running Metrowerks Java?)

You're running Metrowerks Java. Go to the far right-hand menu and select Metrowerks Java to enter that application. Then select Quit from the File menu. This will return you to the CodeWarrior IDE. Now try compiling again.

Exception in thread...

Look at the word at the end of the first line. This is the exception name. Look it up under Exceptions below. For example, the relevant word for the following line

Exception in thread "AWT-macos" java.lang.ArrayIndexOutOfBoundsException: 2

is ArrayIndexOutOfBoundsException.

Identifier expected

If the problem is with a function that you're trying to add to the program, you should place the function within the braces after ``class AddBigNumbers'' (or whatever class the file you're looking at defines). This means that the function definition should come just before the definition of the function you're supposed to write.

KeyServer not found

The problem is not yours; the computer you're using is at fault. Try using another computer. If it still doesn't work, use yet another computer. If this doesn't work, well, find a person running the cluster and see what they can say about it.

The droplet cannot launch because it can't launch Metrowerks Java.

Quit all applications but Finder and CodeWarrior IDE. (You can reach these through the far right-hand menu.)

Exceptions

ArrayIndexOutOfBoundsException

You are attempting to access an array at an index that doesn't exist. Remember a Java array arr is numbered from 0 to arr.length - 1. You are probably accessing arr[arr.length]. Exactly which index of the array you're illegally accessing is revealed by the number immediately following the colon after the exception name.