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());
}
}
