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Java基础泛型接口的使用


 

 
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。