Sunday, September 26, 2010

Static Inner Classes

Consider the following Java code fragment:
public class A
int y;

public static class B
int x;

void f () {}
This fragment defines the class A which contains an static inner class B. A static inner class behaves like any ``outer'' class. It may contain methods and fields, and it may be instantiated like this:
A.B object = new A.B ();
This statement creates an new instance of the inner class B.
Given such an instance, we can invoke the f method in the usual way:
It is not necessarily the case that an instance of the outer class A exists even when we have created an instance of the inner class. Similarly, instantiating the outer class A does not create any instances of the inner class B.
The methods of a static inner class may access all the members (fields or methods) of the inner class but they can access only static members (fields or methods) of the outer class. Thus, f can access the field x, but it cannot access the field y.

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