Public vs Private inner classes in Java

Question

I was reading introduction to Java programming and it does not have a good explanation regarding this topic and it made me wonder why should someone use a private inner class in java instead of using a public one.

They both can be used only by the outer class.

Answer 1

Your claim They both can be used only by the outer class. is wrong:

public class A {
    private class B {}
    public class C {}
    public C getC() { 
        return new C();
    }
    public B getB() {
        return new B();
    }

}
public class Tryout {
    public static void main(String[] args) {
        A a = new A();
        A.B b = a.getB(); //cannot compile
        A.C c = a.getC(); //compiles perfectly
    }
}

Note that you can actually have an instance of A.C in another class and refer to it as C (including all its public declaration), but not for A.B.

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From this you can understand, you should use private/public modifier for inner classes the same way you use it generally.