从头认识java-13.3 泛型接口的使用

这一章节我们来讨论一下泛型接口的使用。

我们以生成器为例子（generator），生成器是工厂方法的一种运用，主要用来创建对象，一般使用工厂方法都是需要输入参数以便取得不同的对象，但是生成器是生成一系列的对象。

代码：

package com.ray.ch13;

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

public class Test implements Generator<Father> {

	private Class<?>[] classes = { Sub1.class, Sub2.class, Sub3.class };

	private Random random = new Random();

	@Override
	public Father next() {
		Father father = null;
		try {
			father = (Father) classes[random.nextInt(3)].newInstance();
		} catch (InstantiationException e) {
			e.printStackTrace();
		} catch (IllegalAccessException e) {
			e.printStackTrace();
		}
		return father;
	}

	public static void main(String[] args) {
		Test test = new Test();
		for (int i = 0; i < 5; i++) {
			System.out.println(test.next());
		}
	}

}

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

class Father {
	private static int counter = 0;
	private final int id = counter++;

	@Override
	public String toString() {
		return "name:" + getClass().getSimpleName() + " id:" + id;
	}
}

class Sub1 extends Father {
}

class Sub2 extends Father {
}

class Sub3 extends Father {
}

输出：

name:Sub3 id:0
name:Sub1 id:1
name:Sub3 id:2
name:Sub3 id:3
name:Sub3 id:4

上面的代码通过生成器生成了5个Father 的自对象Sub，在创建的过程中，生成器不需要输入参数，直接是生成一些列Father的子类对象。

我们修改一下上面的代码，使它满足foreach的使用（就是实现Iterable接口）：

package com.ray.ch13;

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

public class Test implements Generator<Father>, Iterable<Father> {
	public Test() {

	}

	private int size = 0;

	public Test(int size) {
		this.size = size;
	}

	private Class<?>[] classes = { Sub1.class, Sub2.class, Sub3.class };

	private Random random = new Random();

	@Override
	public Father next() {
		Father father = null;
		try {
			father = (Father) classes[random.nextInt(3)].newInstance();
		} catch (InstantiationException e) {
			e.printStackTrace();
		} catch (IllegalAccessException e) {
			e.printStackTrace();
		}
		return father;
	}

	public static void main(String[] args) {
		Test test = new Test();
		for (int i = 0; i < 5; i++) {
			System.out.println(test.next());
		}
		System.out.println("------------------");
		for (Father father : new Test(5)) {
			System.out.println(father);
		}
	}

	@Override
	public Iterator<Father> iterator() {
		return new FatherIterator();
	}

	class FatherIterator implements Iterator<Father> {
		private int count = size;

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

		@Override
		public Father next() {
			count--;
			return Test.this.next();
		}

		@Override
		public void remove() {
			throw new UnsupportedOperationException();
		}
	}
}

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

class Father {
	private static int counter = 0;
	private final int id = counter++;

	@Override
	public String toString() {
		return "name:" + getClass().getSimpleName() + " id:" + id;
	}
}

class Sub1 extends Father {
}

class Sub2 extends Father {
}

class Sub3 extends Father {
}

输出：

name:Sub3 id:0
name:Sub1 id:1
name:Sub3 id:2
name:Sub3 id:3
name:Sub3 id:4
------------------
name:Sub3 id:5
name:Sub1 id:6
name:Sub1 id:7
name:Sub2 id:8
name:Sub3 id:9

参数化的接口确保next（）的返回类型。

我们下面再看另一个例子，是著名的数学题目斐波那契数列：

package com.ray.ch13;

public class Test implements Generator<Integer> {

	private Integer count = 0;

	@Override
	public Integer next() {
		return fib(count++);
	}

	private Integer fib(int param) {
		if (param < 2) {
			return 1;
		}
		return fib(param - 2) + fib(param - 1);
	}

	public static void main(String[] args) {
		Test test = new Test();
		for (int i = 0; i < 10; i++) {
			System.out.print(test.next() + " ");
		}
	}
}

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

输出：

1 1 2 3 5 8 13 21 34 55

总结：这一章节主要展示了泛型接口的使用。

这一章节就到这里，谢谢。

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