增强for循环 

  1 import java.util.ArrayList;
  2 import java.util.HashMap;
  3 import java.util.Iterator;
  4 import java.util.LinkedHashMap;
  5 import java.util.List;
  6 import java.util.Map;
  7 import java.util.Map.Entry;
  8 import java.util.Set;
  9 
 10 import org.junit.Test;
 11 
 12 public class Demo {
 13 
 14     /**
 15      * 增强for
 16      */
 17     public static void main(String[] args) {
 18 
 19     }
 20 
 21     public void test2() {
 22 
 23         List list = new ArrayList();
 24 
 25         list.add(1);
 26         list.add(2);
 27         list.add(3);
 28 
 29         for (Object obj : list) {
 30 
 31             int i = (Integer) obj;
 32             System.out.println(i);
 33 
 34         }
 35     }
 36 
 37     @Test
 38     public void test3() {
 39 
 40         Map map = new HashMap();
 41 
 42         map.put(1, "aaa");
 43         map.put(2, "bbb");
 44         map.put(3, "ccc");
 45 
 46         Set set = map.keySet();
 47         Iterator it = set.iterator();
 48 
 49         while (it.hasNext()) {
 50 
 51             int key = (Integer) it.next();
 52             String value = (String) map.get(key);
 53 
 54             System.out.println(key + ":" + value);
 55 
 56         }
 57     }
 58 
 59     @Test
 60     public void test4(){
 61         
 62         Map map = new LinkedHashMap();
 63         
 64         map.put(1, "aaa");
 65         map.put(2, "bbb");
 66         map.put(3, "ccc");
 67         
 68         Set set = map.entrySet();
 69         Iterator it = set.iterator();
 70         
 71         while(it.hasNext()){
 72             
 73             Map.Entry entry =  (Entry) it.next();
 74             int key =  (Integer) entry.getKey();
 75             String value = (String) entry.getValue();
 76             
 77             System.out.println(key+":"+value);
 78             
 79         }
 80     }
 81         
 82     @Test
 83     public void test5(){
 84         
 85         Map map = new HashMap();
 86         
 87         map.put(1, "aaa");
 88         map.put(2, "bbb");
 89         map.put(3, "ccc");
 90         
 91         //增强for取map的第一种方式
 92         for(Object obj : map.keySet()){
 93             int key = (Integer) obj;
 94             String value = (String) map.get(key);
 95             
 96             System.out.println(key + ":" + value);
 97             
 98         }
 99     }
100     
101     @Test
102     public void test6(){
103         
104         Map map = new HashMap();
105         
106         map.put(1, "aaa");
107         map.put(2, "bbb");
108         map.put(3, "ccc");
109         
110         //增强for取map的二种方式
111         for(Object obj : map.entrySet()){
112             
113             Map.Entry entry = (Entry) obj;
114             
115             int key = (Integer) entry.getKey();
116             String value = (String) entry.getValue();
117             
118             System.out.println(key + ":" + value);
119             
120         }
121     }
122     
123     //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
124     @Test
125     public void test7(){
126         
127         int arr[] = {1,2,3};
128         
129         for(int i : arr){
130             
131             i=10;
132         }
133         
134         System.out.println(arr[0]);
135         System.out.println(arr[1]);
136         System.out.println(arr[2]);
137         
138     }
139     
140 }
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posted @ 2014-06-14 21:05  是但哥  阅读(133)  评论(0)    收藏  举报