Simulating Multiple Inheritance in Java
Article Author: Mike Van Atter
From Book: CodeNotes for Java
Date Published: February 1, 2002
Purpose of Multiple Inheritance
Multiple inheritance allows a single class to extend two parent classes and thus provide the methods of both parent classes. Unlike C++, Java does not eXPlicitly support multiple inheritance, allowing a class to extend only a single parent class. However, as we will show in this article, it is possible to simulate multiple inheritance, allowing a single class to provide the methods, and the respective implementations, of two parent classes. The strategy that is introdUCed in this article is also easily extendible to provide inheritance of three or more parent classes.
Simulating Multiple Inheritance
In this article we will use a simple example to demonstrate how to simulate multiple inheritance in Java. We will begin with the NextOdd and NextEven classes, shown in Listing 1.1 and Listing 1.2 respectively. We will then create a new class, which we will call EvenOdd, that provides the functionality of both classes.
// Repeated calls to the getNextOdd method will
return the next
// odd number (i.e. the first call will return 1, the second
// call 3, etc.
public class NextOdd {
// the last odd number returned by the getNextOdd method
private int lastOdd = -1;
public NextOdd() {
this.lastOdd = -1;
} // NextOdd
// selects a different starting point for the odd numbers
// ensures that the starting point is in fact an odd number
public NextOdd(int start) {
this.lastOdd = ((int)start/2) * 2 + 1;
} // NextOdd
// Retrieves the next odd number
public int getNextOdd() {
return lastOdd += 2;
} // getNext
} // NextOdd
Listing 1.1: NextOdd.java
// Repeated calls to the getNextEven method will
return the
// next even number (i.e the first call will return 0, the
// second call will return 2, etc.)
public class NextEven {
// the last even number returned by getNextEven
private int lastEven = -2;
public NextEven() {
this.lastEven = -2;
} // NextEven
// selects a different starting point for the even numbers
// ensures that the starting point is in fact an even #
public NextEven(int start) {
this.lastEven = ((int)(start/2)) * 2;
} // constructor
// retrieves the next even number
