Java-增强for循环（学习笔记）

增强for循环：简化迭代器书写

一、增强for循环的简单实例

public class Demo{public static void main(String[] args){    int arr[] = {1,2,3};    /**    *增强for    */    for(int num : arr){     System.out.println(num);    }}}

二、增强for循环的几种应用场景

import java.util.ArrayList;import java.util.List;/**    *增强for    */public class Demo{//数组的简单应用public void test1(){int arr[] = {1,2,3};for(int num : arr){System.out.println(num);}}

//链表的简单应用public void test2(){List list = new ArrayList();list.add(1);list.add(2);list.add(3);for(Object obj : list){ int i = (Integer)obj; System.out.println(i);}    }

//map的应用实例//传统方式1public void test3(){Map map = new LinkedHashMap();//不同于HashMap的无顺序形式map.put("1","aaa");map.put("2","bbb");map.put("3","ccc");Set set = map.keySet();Iterator  it = set.iterator();while(it.hasNext()){String key = (String)it.next();String value = (String)map.get(key);System.out.println(key + "=" + value);}}

//传统方式2public void test4(){Map map = new LinkedHashMap();map.put("1","aaa");map.put("2","bbb");map.put("3","ccc");Set set = map.entrySet();Iterator  it = set.iterator();while(it.hasNext()){Map.Entry entry = (Entry)it.next();String key = (String)entry.getKey();String value = (String)entry.getValue();System.out.println(key + "=" + value);}}

//增强for循环应用于map的第一种方法public void test5(){Map map = new LinkedHashMap();map.put("1","aaa");map.put("2","bbb");map.put("3","ccc");for(Object obj : map.keySet()){String key = (String) obj;Stringg value = (String) map.get(key);System.out.println(key + "=" + value);}}

//增强for循环应用于map的第二种方法public void test5(){Map map = new LinkedHashMap();map.put("1","aaa");map.put("2","bbb");map.put("3","ccc");for(Object obj : map.entrySet()){Map.Entry entry = (entry) obj;String key = (String) entry.getKey();Stringg value = (String) entry.getVnalue();System.out.println(key + "=" + value);}}}

三、增强for循环需要注意的问题

1.只适合取数据，不能更改数据；

2.只用于数组，或实现Iterable接口的集合类上；set，list。