實體Person類

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;  }     }

測試ArrayList的主程式

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迴圈測試結果："+testFor());
		System.out.println("foreach迴圈測試結果："+testForeach());
		System.out.println("iterator迴圈測試結果："+testIterator());
	}
	
	//初始化集合
	public static void init(){
		for (int i = 0; i <COUNT; i++) {
			persons.add(new Person("第"+i+"個元素",i));
		}
	}
	//for迴圈便利集合
	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迴圈便利集合
	public static long testForeach(){
		long start = System.nanoTime();
		Person p = null;
		for (Person person : persons) {
			p = person;
		}
		return (System.nanoTime()-start)/1000;
	}
	//iterator迴圈便利集合
	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;
	}
	
}

 ArrayList測試結果

測試LinkedList的主程式

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迴圈測試結果："+testFor());
		System.out.println("foreach迴圈測試結果："+testForeach());
		System.out.println("iterator迴圈測試結果："+testIterator());
	}
	
	//初始化集合
	public static void init(){
		for (int i = 0; i <COUNT; i++) {
			persons.add(new Person("第"+i+"個元素",i));
		}
	}
	//for迴圈便利集合
	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迴圈便利集合
	public static long testForeach(){
		long start = System.nanoTime();
		Person p = null;
		for (Person person : persons) {
			p = person;
		}
		return (System.nanoTime()-start)/1000;
	}
	//iterator迴圈便利集合
	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;
	}
	
}
 

LinkedList測試結果：

記錄的存取方式有兩種：

             一種是順序儲存（陣列，ArrayList..）可以根據其下標找到對應的記錄

            另一種是連結儲存(LinkedList..)連結儲存(拿單鏈表為例)則必須找到其前一個記錄的位置才能夠找到本記錄。

根據以上可以得到的結果是：for迴圈便於訪問順序儲存的記錄，而foreach和迭代器便於訪問連結儲存。