增强for循环

 import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.Iterator;
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Map.Entry;
 import java.util.Set;
 
 import org.junit.Test;
 
 public class Demo {
 
     /**
      * 增强for
      */
     public static void main(String[] args) {
 
     }
 
     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);
 
         }
     }
 
     @Test
     public void test3() {
 
         Map map = new HashMap();
 
         map.put(1, "aaa");
         map.put(2, "bbb");
         map.put(3, "ccc");
 
         Set set = map.keySet();
         Iterator it = set.iterator();
 
         while (it.hasNext()) {
 
             int key = (Integer) it.next();
             String value = (String) map.get(key);
 
             System.out.println(key + ":" + value);
 
         }
     }
 
     @Test
     public 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();
             int key =  (Integer) entry.getKey();
             String value = (String) entry.getValue();
 
             System.out.println(key+":"+value);
 
         }
     }
 
     @Test
     public void test5(){
 
         Map map = new HashMap();
 
         map.put(1, "aaa");
         map.put(2, "bbb");
         map.put(3, "ccc");
 
         //增强for取map的第一种方式
         for(Object obj : map.keySet()){
             int key = (Integer) obj;
             String value = (String) map.get(key);
 
             System.out.println(key + ":" + value);
 
         }
     }
 
     @Test
     public void test6(){
 
         Map map = new HashMap();
 
         map.put(1, "aaa");
         map.put(2, "bbb");
         map.put(3, "ccc");
 
         //增强for取map的二种方式
         for(Object obj : map.entrySet()){
 
             Map.Entry entry = (Entry) obj;
 
             int key = (Integer) entry.getKey();
             String value = (String) entry.getValue();
 
             System.out.println(key + ":" + value);
 
         }
     }
 
     //使用增强for需要注意的问题：增强for只合适取数据,要修改数组或集合的数据，使用传统方法
     @Test
     public void test7(){
 
         int arr[] = {1,2,3};
 
         for(int i : arr){
 
             i=10;
         }
 
         System.out.println(arr[0]);
         System.out.println(arr[1]);
         System.out.println(arr[2]);
 
     }
 
 }