Accessing private inner class in the same package

Question

I have two compilation units:

public class OuterClass{

    private static class InnerClass{

        public String test(){
            return \"testing123\";
           


        

Answer 1

The javap signature for an inner class:

class modifiers.OuterClass$InnerClass extends java.lang.Object{
    final modifiers.OuterClass this$0;
    public java.lang.String test();
}

When it comes to bytecode (i.e. runtime) there is no such thing as a private class. This is a fiction maintained by the compiler. To the reflection API, there's a package-accessible type with a public member method.

Actual access modifiers are defined in the JVM spec:

Flag Name      Value   Interpretation
ACC_PUBLIC     0x0001  Declared public; may be accessed from outside its package.
ACC_FINAL      0x0010  Declared final; no subclasses allowed.
ACC_SUPER      0x0020  Treat superclass methods specially when invoked by the
                       invokespecial instruction.
ACC_INTERFACE  0x0200  Is an interface, not a class.
ACC_ABSTRACT   0x0400  Declared abstract; may not be instantiated. 

Answer 2

Private access modifier is stronger than package one (i.e. not having an access modifier at all in Java). Hence private elements of class - be it fields, methods or inner classes - are accessible only within that class.