java迭代器和for循环,迭代器和For循环的效率比较 | 学步园

昨儿晚上宿舍讨论到迭代器的问题，今天有时间我就写了个小东西看了看两者的效率差别。发现效率差的还真大。

先上代码。代码很简单。

主程序测试类：TestArrayList.java

package com.test.arrayList;

import java.util.ArrayList;

import java.util.Iterator;

import java.util.List;

public class TestArrayList {

private static final int COUNT =700000;

private static List persons = new ArrayList();

public static void main(String args[]) {

init();

System.out.println("For遍历测试：" + testFor()+ "微秒");

System.out.println("迭代器遍历测试：" +testIterator()+ "微秒");

System.out.println("有人很喜欢的foreach测试：" +testForEach()+ "微秒");

}

public static void init() {

Person person = null;

for (int i = 0; i < COUNT; i++) {

person = new Person("第" + i + "个", i, i * 100);

persons.add(person);

}

}

public static long testIterator() {

long start = System.nanoTime();

Person person = null;

for (Iterator it = persons.iterator(); it.hasNext();) {

person = it.next();

}

return (System.nanoTime() - start) / (1000);

}

public static long testFor() {

long start = System.nanoTime();

Person person = null;

for (int i = 0; i < persons.size(); i++) {

person = persons.get(i);

}

return (System.nanoTime() - start) / (1000);

}

public static long testForEach() {

long start = System.nanoTime();

Person person = null;

for (Person p : persons) {

person = p;

}

return (System.nanoTime() - start) / (1000);

}

}

实体Person类。放到容器里面的。

Person.java

package com.test.arrayList;

public class Person {

private String name;

private int age;

private double money;

public Person(String name, int age, double money) {

this.name = name;

this.age = age;

this.money = money;

}

getter();

setter();

}

开始测试：

结果附上图：

看到差别了吧。上面的测试是万级别的测试。一般效率影响不大。

要多说的是foreach效率和迭代器效率差不多。