1. David Stotts Computer Science Department UNC Chapel Hill

2. Software Engineering (Bridge Design Pattern)

3.  The Bridge design pattern is used to separate the abstract user level API from the backend implementation  We can write client code to talk to the front end API  We can plug in different back end implementations without changing client code

7. //=== interface side ============================== class Stack { // 3. Create an interface/wrapper class that protected StackImp imp; // "hasa" impl object and delegates public Stack( String s ) { // all requsts to it if (s.equals("java")) { imp = new StackImpJava(); // can add more implementation options //} else if (s.equals("list")) { // imp = new StackImpList(); } else { imp = new StackImpMine(); } } public Stack() { this( "java" ); } public void push( int in ) { imp.push( new Integer(in) ); } public int pop() { return ((Integer)imp.pop()).intValue(); } public int top() { return ((Integer)imp.peek()).intValue(); } public boolean isEmpty() { return imp.empty(); } }

8. //=== implementation side ========================= interface StackImp { // an implementation/body base class Object push( Object o ); Object peek(); // top Object pop(); boolean empty(); } class StackImpJava extends java.util.Stack implements StackImp { } class StackImpMine implements StackImp { private Object[] items = new Object[200]; 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; } }

9. //==== client code ================================== class BridgeDemo { public static void main( String[] args ) { Stack[] stacks = { new Stack("java"), new Stack("mine"), new StackStomp("java"), new StackStomp("mine") }; //Stack st = new Stack("java"); Stack st = new Stack("mine"); //Stack st = new StackStomp("mine"); st.push(12); st.push(14); st.push(12); st.push(47); st.push(31); System.out.println(st.pop()); System.out.println(st.pop()); System.out.println(st.pop()); for (int num,i=0; i<25; i++) { num = (int)(Math.random() * 1000) % 80; // push this random num onto each stack for (int j=0; j<stacks.length; j++) stacks[j].push(num); } for (int num,i=0; i<stacks.length; i++) { while ( ! stacks[i].isEmpty()) System.out.print( stacks[i].pop() + " " ); System.out.println(); }

10. // add more stack interface variants class StackStomp extends Stack { private int totalStomped = 0; private int max; private int size=0; public StackStomp() { super("java"); max=10;} public StackStomp(String s) { super(s); max=10; } public StackStomp(String s, int size) { super(s); max=size;} public StackStomp(int size) { super("java"); max=size; } public int reportStomped() { return totalStomped; } public void push (int elt) { if (size==max) { // stomp one totalStomped++; Stack st = new Stack(); for (int i=0; i<size; i++) { st.push(super.pop()); } st.pop(); for (int i=0; i<size-1; i++) { super.push(st.pop()); } super.push(elt); } else { // ok to do the push size++; super.push(elt); } public int pop() { if (size>0) { size--; return super.pop(); } else return -1; }

11. Beyond this is just templates