Java inner class visibility puzzle

Question

Consider the following case:

public class A {
  public A() { b = new B(); }
  B b;
  private class B { }
}

From a warning in Eclipse I quot

Answer 1

Inner classes are essentially a hack introduced in Java 1.1. The JVM doesn't actually have any concept of an inner class, and so the compiler has to bodge it. The compiler generates class B "outside" of class A, but in the same package, and then adds synthetic accessors/constructors to it to allow A to get access to it.

When you give B a protected constructor, A can access that constructor since it's in the same package, without needing a synthetic constructor to be added.