迭代器和for循环的效率比较

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package com.zhang.loop;
public class Person {
 private String a;
 private int b;
 public Person(String a, int b) {
  super();
  this.a = a;
  this.b = b;
 }
 public String getA() {
  return a;
 }
 public void setA(String a) {
  this.a = a;
 }
 public int getB() {
  return b;
 }
 public void setB(int b) {
  this.b = b;
 }
 
 
}
 

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package com.zhang.loop;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;

public class TestArrayList {
	private static final int COUNT = 800000;
	private static List<Person> persons = new ArrayList<Person>();
	
	public static void main(String[] args) {
		init();
		System.out.println("for循环测试结果："+testFor());
		System.out.println("foreach循环测试结果："+testForeach());
		System.out.println("iterator循环测试结果："+testIterator());
	}
	
	//初始化集合
	public static void init(){
		for (int i = 0; i <COUNT; i++) {
			persons.add(new Person("第"+i+"个元素",i));
		}
	}
	//for循环便利集合
	public static long testFor(){
		long start = System.nanoTime();
		Person p = null;
		for (int i = 0; i < persons.size(); i++) {
			p = persons.get(i);
		}
		return (System.nanoTime()-start)/1000;
	}
	//foreach循环便利集合
	public static long testForeach(){
		long start = System.nanoTime();
		Person p = null;
		for (Person person : persons) {
			p = person;
		}
		return (System.nanoTime()-start)/1000;
	}
	//iterator循环便利集合
	public static long testIterator(){
		long start = System.nanoTime();
		Person p = null;
		Iterator<Person> itreator = persons.iterator();
		while(itreator.hasNext()){
			p = itreator.next();
		}
		return (System.nanoTime()-start)/1000;
	}
	
}

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package com.zhang.loop;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;

public class TestArrayList {
	private static final int COUNT = 8000;
	private static List<Person> persons = new LinkedList<Person>();
	
	public static void main(String[] args) {
		init();
		System.out.println("for循环测试结果："+testFor());
		System.out.println("foreach循环测试结果："+testForeach());
		System.out.println("iterator循环测试结果："+testIterator());
	}
	
	//初始化集合
	public static void init(){
		for (int i = 0; i <COUNT; i++) {
			persons.add(new Person("第"+i+"个元素",i));
		}
	}
	//for循环便利集合
	public static long testFor(){
		long start = System.nanoTime();
		Person p = null;
		for (int i = 0; i < persons.size(); i++) {
			p = persons.get(i);
		}
		return (System.nanoTime()-start)/1000;
	}
	//foreach循环便利集合
	public static long testForeach(){
		long start = System.nanoTime();
		Person p = null;
		for (Person person : persons) {
			p = person;
		}
		return (System.nanoTime()-start)/1000;
	}
	//iterator循环便利集合
	public static long testIterator(){
		long start = System.nanoTime();
		Person p = null;
		Iterator<Person> itreator = persons.iterator();
		while(itreator.hasNext()){
			p = itreator.next();
		}
		return (System.nanoTime()-start)/1000;
	}
	
}