The Java Type System - Java in a Nutshell - page 159

You can also use the import static directive to import a
static member type. See “Packages and the Java Namespace”
on page 88 in Chapter 2 for details on import and import
static .

However, importing a nested type obscures the fact that that type is closely associ‐
ated with its containing type—which is usually important information—and as a
result it is not commonly done.

Nonstatic Member Classes
A nonstatic member class is a class that is declared as a member of a containing class
or enumerated type without the static keyword:

• If a static member type is analogous to a class field or class method, a nonstatic
member class is analogous to an instance field or instance method.
• Only classes can be nonstatic member types.
• An instance of a nonstatic member class is always associated with an instance
of the enclosing type.
• The code of a nonstatic member class has access to all the fields and methods
(both static and non- static ) of its enclosing type.
• Several features of Java syntax exist specifically to work with the enclosing
instance of a nonstatic member class.

m

e

Example 4-2 shows how a member class can be defined and used. This example
extends the previous LinkedStack example to allow enumeration of the elements on
the stack by defining an iterator() method that returns an implementation of the
java.util.Iterator interface. The implementation of this interface is defined as a
member class.

Example 4-2. An iterator implemented as a member class

import java.util.Iterator ;

public class LinkedStack {

// Our static member interface
public interface Linkable {
public Linkable getNext ();
public void setNext ( Linkable node );
}

// The head of the list
private Linkable head ;

// Method bodies omitted here