java 泛型2——泛型接口

泛型也可以应用于接口，这边以生成器gennerator为例，生成器是一种专门负责创建对象的类。实际上，这就是工厂方法设计模式的一种应用。不过，当使用生成器创建新的对象时，他不需要任何参数，而工厂方法一般需要参数。也就是说，生成器无需额外信息即可创建对象。

首先生成器接口定义如下：

package com.zy.test;

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

然后定义一些需要的类：

package com.zy.test;

public class Coffee {
    private static long count = 0;
    private final long id = count++;
    public String toString() {
        return getClass().getSimpleName() + " " + id;
    }
}

class Latte extends Coffee {}
class Mocha extends Coffee {}
class Cappuccino extends Coffee {}
class Americano extends Coffee {}
class Breve extends Coffee {}

现在编写一个类实现Generator<Coffee>接口，它能够随机生成不同类型的Coffee对象：

package com.zy.test;

import java.util.Iterator;
import java.util.Random;

public class CoffeeGenerator implements Generator<Coffee>, Iterable<Coffee> {
    private Class[] types = { Latte.class, Mocha.class, Cappuccino.class, Americano.class, Breve.class};
    private static Random rand = new Random(47);
    public CoffeeGenerator() {
        
    }
    private int size;
    
    public CoffeeGenerator(int size) {
        this.size = size;
    }

    @Override
    public Coffee next() {
        try {
            return (Coffee)types[rand.nextInt(types.length)].newInstance();
        } catch (InstantiationException | IllegalAccessException e) {
            e.printStackTrace();
            throw new RuntimeException(e);
        }
    }

    class CoffeeIterator implements Iterator<Coffee> {

        int count = size;

        @Override
        public boolean hasNext() {
            return count > 0;
        }

        @Override
        public Coffee next() {
            count--;
            return CoffeeGenerator.this.next();
        }
        
        public void remove() {
            throw new UnsupportedOperationException();
        }
    }
    
    
    @Override
    public Iterator<Coffee> iterator() {
        return new CoffeeIterator();
    }
    
    public static void main(String[] args) {
        CoffeeGenerator gen = new CoffeeGenerator();
        for (int i = 0; i < 5; i++) {
            System.out.println(gen.next());
        }
        for (Coffee c : new CoffeeGenerator(5)) {
            System.out.println(c);
        }
    }

}

输出：

Americano 0
Latte 1
Americano 2
Mocha 3
Mocha 4
Breve 5
Americano 6
Latte 7
Cappuccino 8
Cappuccino 9