Transcript Bridge pattern

David Stotts
Computer Science Department
UNC Chapel Hill
Software Engineering
(Bridge Design Pattern)

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
//=== 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(); }
}
//=== implementation side =========================
interface
Object
Object
Object
boolean
}
StackImp { // an implementation/body base class
push( Object o );
peek(); // top
pop();
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; }
}
//==== 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());
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.println();
}
}
}
System.out.print( stacks[i].pop() + "
" );
// add more stack interface variants
class StackStomp extends Stack {
private int totalStomped = 0;
private int max;
private int size=0;
public
public
public
public
public
StackStomp() { super("java"); max=10;}
StackStomp(String s) { super(s); max=10; }
StackStomp(String s, int size) { super(s); max=size;}
StackStomp(int size) { super("java"); max=size; }
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;
}
}
Beyond this is just templates