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();@Overridepublic 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++;@Overridepublic 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();@Overridepublic 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);}}@Overridepublic Iterator<Father> iterator() {return new FatherIterator();}class FatherIterator implements Iterator<Father> {private int count = size;@Overridepublic boolean hasNext() {return count > 0;}@Overridepublic Father next() {count--;return Test.this.next();}@Overridepublic void remove() {throw new UnsupportedOperationException();}}}interface Generator<T> {T next();}class Father {private static int counter = 0;private final int id = counter++;@Overridepublic 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;@Overridepublic 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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