Interface Type Variables

Java Tutorials - Herong's Tutorial Examples

∟Interface Type Variables

This section describes how to use an interface type variable to store references to objects of classes that implemented this interface.

Interface type variables are used in Java following these basic rules:

An interface type variable can store the reference of an object of a class that implemented this interface.
The dot operator of an interface type variable can only invoke methods declared in this interface.

Here is a tutorial example program that shows you how to use interface type variables:

/* InterfaceTypeVariable.java
 * Copyright (c) HerongYang.com. All Rights Reserved.
 */
import java.util.*;
class InterfaceTypeVariable {
   public static void main(String[] a) {
      java.io.PrintStream o = System.out;

      // assigning the reference of a LinkedList object
      LinkedList<String> bookList = new LinkedList<String>();

      // assigning the reference to an implemented interface
      // LinkedList<E> implements Queue<E>
      Queue<String> bookQueue = bookList;

      // accessing interface methods
      bookQueue.add("Java Tutorials");
      bookQueue.add("PHP Tutorials");
      String next = bookQueue.remove();

      o.println("Next book in the queue = "+next);
   }
}