ArrayList集合遍历的八种方式

ArrayList集合遍历的七种方式

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Iterator;
import java.util.List;
import java.util.ListIterator;

public class Ergodic {
  public static void main(String[] args) {
    
    System.out.println("ArrayList集合的遍历");
    List list = new ArrayList();
    list.add(1);
    list.add(2);

    
    System.out.println("1.for循环:");
    for(int i = 0; i<list.size(); i++) {
      System.out.println(list.get(i));
    }

    
    System.out.println("2.foreach循环:");
    for(Object l : list) {
      System.out.println(l);
    }

    
                System.out.println("3.链表变为数组内容后遍历:");
                Integer[] inteArray = new Integer[list.size()];
                list.toArray(inteArray);
                for(int inte : inteArray) {
                    System.out.println(inte);
                }


    System.out.println("4.while迭代器遍历:");
    Iterator iterator1 = list.iterator();
    while(iterator1.hasNext()) {// hasNext()方法:判断该指针所指位置是否有元素
      System.out.println(iterator1.next());// next()方法:1.获取该指针指向的元素 2.并把指针指向下一个元素(即指针后移一位)
    }


    System.out.println("5.for迭代器遍历:");
    //该处将while改为for循环遍历,可以当遍历完后便释放迭代器对象,更节省内存
    for(Iterator iterator3 = list.iterator(); iterator3.hasNext() ;) {
      System.out.println(iterator3.next());
    }

    
    System.out.println("6.1 ListIterator迭代器向后遍历:");
    ListIterator iterator2 = list.listIterator();
    while(iterator2.hasNext()) {// 将list集合先从头向后遍历,指针指向最后
      System.out.println(iterator2.next());
    }


    System.out.println("6.2 ListIterator迭代器向前遍历");
    while(iterator2.hasPrevious()) {// 将list集合从末尾先前遍历,指针指到第一个元素
      System.out.println(iterator2.previous());
    }   
  }
}      

对于集合的遍历,推荐下面代码,节省内存.

for(Iterator iterator3 = list.iterator(); iterator3.hasNext() ;) {

            System.out.println(iterator3.next());

        }

还有对于集合的foreach遍历集合,其实就是反编译后就是上面的代码.若想节省内存还是推荐上面代码. 

Java8可以使用Stream API来遍历集合

// List集合遍历的第八种方式
list.stream().forEach(System.out::println);      

集合反编译代码

// Decompiled by Jad v1.5.8e2. Copyright 2001 Pavel Kouznetsov.
// Jad home page: http://kpdus.tripod.com/jad.html
// Decompiler options: packimports(3) fieldsfirst ansi space 
// Source File Name:   Ergodic.java

import java.io.PrintStream;
import java.util.*;

public class Ergodic
{

  public Ergodic()
  {
  }

  public static void main(String args[])
  {
    
    System.out.println("ArrayList集合的遍历");
    List list = new ArrayList();
    list.add(Integer.valueOf(1));
    list.add(Integer.valueOf(2));


    System.out.println("1.for循环:");
    for (int i = 0; i < list.size(); i++)
      System.out.println(list.get(i));

    System.out.println("2.foreach循环:");
    Object l;
    for (Iterator iterator = list.iterator(); iterator.hasNext(); System.out.println(l))
      l = iterator.next();

    System.out.println("3.链表变为数组内容后遍历:");
    Integer inteArray[] = new Integer[list.size()];
    list.toArray(inteArray);
    Integer ainteger[];
    int j1 = (ainteger = inteArray).length;
    for (int i1 = 0; i1 < j1; i1++)
    {
      int inte = ainteger[i1].intValue();
      System.out.println(inte);
    }

    System.out.println("4.while迭代器遍历:");
    for (Iterator iterator1 = list.iterator(); iterator1.hasNext(); System.out.println(iterator1.next()));

    System.out.println("5.for迭代器遍历:");
    for (Iterator iterator3 = list.iterator(); iterator3.hasNext(); System.out.println(iterator3.next()));

    System.out.println("6.1 ListIterator迭代器向后遍历:");
    ListIterator iterator2;
    for (iterator2 = list.listIterator(); iterator2.hasNext(); System.out.println(iterator2.next()));

    System.out.println("6.2 ListIterator迭代器向前遍历");
    for (; iterator2.hasPrevious(); System.out.println(iterator2.previous()));
  }
}      

数组

System.out.println("数组的遍历");
    int[] a = new int[] {1,2};


    System.out.println("1.for循环:");
    for (int i = 0; i < a.length; i++) {
      System.out.println(a[i]);
    }


    System.out.println("2.foreach循环:");
    for(int b : a) {
      System.out.println(b);
    }

    
    System.out.println("3.Arrays工具类:");
    System.out.println(Arrays.toString(a));      

数组反编译代码

System.out.println("数组的遍历");
    int a[] = {
      1, 2
    };
    System.out.println("1.for循环:");
    for (int i = 0; i < a.length; i++)
      System.out.println(a[i]);

    System.out.println("2.foreach循环:");
    int ai[];
    int k = (ai = a).length;
    for (int j = 0; j < k; j++)
    {
      int b = ai[j];
      System.out.println(b);
    }

    System.out.println("3.Arrays工具类:");
    System.out.println(Arrays.toString(a));