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。

public interface Generator<T> {
    T next();
    boolean hasNext();
}

public class CoffeeGenerator implements Generator<Coffee> {

    private int[] numList;

    private int pos;

    public CoffeeGenerator(int[] numList) {
        this.numList = numList;
        pos = 0;
    }

    @Override
    public Coffee next() {
        switch (numList[pos++]) {
        case Cappuccino.NUM:
            return new Cappuccino();
        case Latte.NUM:
            return new Latte();
        case Mocha.NUM:
            return new Mocha();
        default:
            return null;
        }
    }

    @Override
    public boolean hasNext() {
        return numList != null && numList.length != 0 && numList.length > pos;
    }
}

public interface Coffee {
    int getPrice();
    void make();
}

public class Cappuccino implements Coffee {

    public final static int NUM = 1;

    Cappuccino() {
        make();
    }

    @Override
    public int getPrice() {
        return 38;
    }

    @Override
    public void make() {
        System.out.println("Making " + getClass().getSimpleName() + "...");
    }
}

public class Latte implements Coffee {

    public final static int NUM = 2;

    Latte() {
        make();
    }

    @Override
    public int getPrice() {
        return 32;
    }

    @Override
    public void make() {
        System.out.println("Making " + getClass().getSimpleName() + "...");
    }
}

public class Mocha implements Coffee {

    public final static int NUM = 3;

    Mocha() {
        make();
    }

    @Override
    public int getPrice() {
        return 35;
    }

    @Override
    public void make() {
        System.out.println("Making " + getClass().getSimpleName() + "...");
    }
}

Main方法测试：

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