Derive the separate implementations from the common abstraction
Create an interface/wrapper class that "has a" and delegates to the impl
Embellish the interface class with derived classes if desired
/** * Create an interface/wrapper class that "has a" * implementation object and delegates all requests to it */ class Stack { protected StackImp imp; public Stack(String s) { if (s.equals("java")) { imp = new StackJava(); } else { imp = new StackMine(); } } public Stack() { this("java"); } public void push(int in) { imp.push(in); } public int pop() { return (Integer) imp.pop(); } public boolean isEmpty() { return imp.empty(); } } /** * Embellish the interface class with derived classes if desired */ class StackHanoi extends Stack { private int totalRejected = 0; public StackHanoi() { super("java"); } public StackHanoi(String s) { super(s); } public int reportRejected() { return totalRejected; } public void push(int in) { if (!imp.empty() && in > (Integer)imp.peek()) { totalRejected++; } else { imp.push(in); } } } /** * Create an implementation/body base class */ interface StackImp { Object push(Object o); Object peek(); boolean empty(); Object pop(); } class StackJava extends java.util.Stack implements StackImp { } /** * Derive the separate implementations from the common abstraction */ class StackMine implements StackImp { private Object[] items = new Object[20]; private int total = -1; public Object push(Object o) { return items[++total] = o; } public Object peek() { return items[total]; } public Object pop() { return items[total--]; } public boolean empty() { return total == -1; } } public class BridgeDemo { public static void main(String[] args) { Stack[] stacks = { new Stack("java"), new Stack("mine"), new StackHanoi("java"), new StackHanoi("mine") }; for (int i=0, num; i < 20; i++) { num = (int)(Math.random() * 1000) % 40; for (Stack stack : stacks) { stack.push(num); } } for (int i=0, num; i < stacks.length; i++) { while (!stacks[i].isEmpty()) { System.out.print( stacks[i].pop() + " "); } System.out.println(); } System.out.println("total rejected is " + ((StackHanoi)stacks[3]).reportRejected()); } }
