Java泛型(2)：泛型接口

泛型不仅可以在类上实现，也可以在接口上实现。JDK中[Iterable<T> <-- Collection<E> <-- List<E>/Queue<E>/Set<E>]都是泛型接口。

下面是一个泛型接口的例子。这是一个一个生成器的例子。生成器用来专门创建对象。这是工厂方法设计模式的一种应用。一般来说生成器只有一个用来生成新的对象的方法。

1 public interface Generator<T> {
2     T next();
3     boolean hasNext();
4 }

 1 public class CoffeeGenerator implements Generator<Coffee> {
 2 
 3     private int[] numList;
 4 
 5     private int pos;
 6 
 7     public CoffeeGenerator(int[] numList) {
 8         this.numList = numList;
 9         pos = 0;
10     }
11 
12     @Override
13     public Coffee next() {
14         switch (numList[pos++]) {
15         case Cappuccino.NUM:
16             return new Cappuccino();
17         case Latte.NUM:
18             return new Latte();
19         case Mocha.NUM:
20             return new Mocha();
21         default:
22             return null;
23         }
24     }
25 
26     @Override
27     public boolean hasNext() {
28         return numList != null && numList.length != 0 && numList.length > pos;
29     }
30 }

1 public interface Coffee {
2     int getPrice();
3     void make();
4 }

 1 public class Cappuccino implements Coffee {
 2 
 3     public final static int NUM = 1;
 4 
 5     Cappuccino() {
 6         make();
 7     }
 8 
 9     @Override
10     public int getPrice() {
11         return 38;
12     }
13 
14     @Override
15     public void make() {
16         System.out.println("Making " + getClass().getSimpleName() + "...");
17     }
18 }

 1 public class Latte implements Coffee {
 2 
 3     public final static int NUM = 2;
 4 
 5     Latte() {
 6         make();
 7     }
 8 
 9     @Override
10     public int getPrice() {
11         return 32;
12     }
13 
14     @Override
15     public void make() {
16         System.out.println("Making " + getClass().getSimpleName() + "...");
17     }
18 }

 1 public class Mocha implements Coffee {
 2 
 3     public final static int NUM = 3;
 4 
 5     Mocha() {
 6         make();
 7     }
 8 
 9     @Override
10     public int getPrice() {
11         return 35;
12     }
13 
14     @Override
15     public void make() {
16         System.out.println("Making " + getClass().getSimpleName() + "...");
17     }
18 }

Main方法测试：

1         Generator<Coffee> coffeeGen = new CoffeeGenerator(new int[] { 1, 3, 2, 1, 1, 3 });
2         int totalPrice = 0;
3         while (coffeeGen.hasNext()) {
4             Coffee coffee = coffeeGen.next();
5             totalPrice += coffee.getPrice(); // Making Cappuccino/Mocha/Latte/Cappuccino/Cappuccino/Mocha...
6         }
7         System.out.println(totalPrice); // 216