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<Person> persons = new ArrayList<Person>();

	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<Person> 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。