Why do two nested classes in Java lead to an exception?

Question

Why is java trowing a NoClassDefFoundError?

The class NestedClassTest has two nested classes, X and Y, inside.

When calling the constructor of NestedClassTest, which instantiates X and Y, java throws an exception when trying to instantiate Y.

public class NestedClassTest {

    private X x = null;
    private Y y = null;

    public NestedClassTest()
    {
        x = new X();
        System.out.println(x.x);
        y = new Y();
        System.out.println(y.y);
    }

    private class X
    {
        public String x = "XXX";
    }

    private class Y
    {
        public String y = "YYY";
    }

    public static void main(String[] args) {
        NestedClassTest t = new NestedClassTest();

    }  
}

This is part of the output:

run:
XXX
Exception in thread "main" java.lang.NoClassDefFoundError: 
    Nestedclasstest/NestedClassTest$Y
    ...
Caused by: java.lang.ClassNotFoundException:
    nestedclasstest.NestedClassTest$Y
    ...

Answer 1

Your code is fine.

Looking at your error you might be having troubles with incorrect packages..

 Exception in thread "main" java.lang.NoClassDefFoundError: 
Nestedclasstest/NestedClassTest$Y
...
Caused by: java.lang.ClassNotFoundException:
nestedclasstest.NestedClassTest$Y

nestedclasstest vs Nestedclasstest. Refer here for reference

just recompile and run again, should work.

Answer 2

There is nothing wrong with that, if you are using eclipse, do a Project, Clean and try again, as the build path needs to be updated.

Answer 3

The code you have posted is not incorrect in and of itself. You difficulties lie elsewhere, with compilation or invocation.

Answer 4

You need to include the NestedClassTest$Y class in the classpath.