Accepted answer

Basically it means the class loader has not loaded the GridSquare[] class. That being said it sounds like a bug in the debugger in some way. The breakpoint association with the code seems to be slightly broken. Either you need to recompile to get the line numbers in sync or some other issue is going on. At that point in the code (after the assignment) it needs to be loaded. Unless getSquares actually returns a subclass (GridSquareSubclass[]) at which point the JVM may not have loaded it because it doesn't need it (yet).


I faced the same problem, i just created a public static void main method, created object of same type and Run As java Application, i then removed main method, it now works fine.


By initializing GridSquare will solve the problem. squares =new GridSquare();


I have seen this happen in Eclipse when you have a subclass's class variables hiding a parent class's variables. Somehow that confuses Eclipse (and generally is a bad idea anyway :). For example:

class A {
   private String a;

class B extends A {
   public String a;


//Give a SIZE to the array:
GridSquare[] squares = GridSquare[this.theGrid.size()];

//Fill each element of the array with the object constructor to avoid the null value
for(int i=0; i<this.theGrid.size(); i++){
    squares[i] = new GridSquare();
    squares[i] = this.theGrid.getSquares(14, 18, 220, 222);


I ran into this error because I was running a unit test on code that uses reflection. I had made a special class for testing all the features of the code. Junit apparently uses a separate classloader for test classes (which makes perfect sense) so my code was not able to use reflection on that class. The stack trace I got was extremely generic (java.lang.InstantiationException) but when I checked in debug mode there was more detail on the Exception object itself (org.eclipse.debug.core.DebugException: com.sun.jdi.ClassNotLoadedException) which led me to this conclusion.

So I moved the special class to the main classloader (by moving the file from src/test/java to src/main/java) and it worked fine. I don't like this solution but I cannot figure out an alternative. In my case it's not a big deal but I can see how this might be a concern for others.

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