13_Review Lecture

# Extends t s forthere is element in s pushspop

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Unformatted text preview: ehaves polymorphically –  “? extends” represent any sub types. –  “? super” represent any super types 20 Enforce Correct Type Parameters Instead of saying: Lunch<Meat, Starch, Soup>! ! We can say: Lunch<M extends Beef, S extends Noodle, C extends Cream>! Support Polymorphism Just like saying: Fruit f = new Apple();! f = new Orange();! ! We can say: Stack<? extends Fruit> sf = new Stack<Apple>();! sf = new Stack<Orange>();! Stack<? super Orange> sf = new Stack<Orange>();! sf = new Stack<Fruit>();! 21 Support Polymorphism Version 4 class Stack<T>{! public void pushAll(Stack<? super T> s){! for(//there is element in me)! s.push(pop());! }! public void popAll(Stack<? extends T> s) {! for(//there is element in s)! push(s.pop());! }! }! Stack<ClassA> s1 = new Stack<ClassA>();! Stack<ClassB> s2 = new Stack<ClassB>();! s2.pushAll(s1); ! s1.popAll(s2); ! 22 PECS Principle •  Producer Extends Consumer Super •  The parameter is a generic container P –  If you are going to go through the elements of P, P is a producer. –  If you are going to add things into P, P is a consumer •  Example: print(ArrayLis...
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