集合Set、List、Map的遍历方法

 1 package com.shellway.javase;
 2 import java.util.ArrayList;
 3 import java.util.Collection;
 4 import java.util.HashSet;
 5 import java.util.Iterator;
 6 import java.util.List;
 7 import java.util.Map;
 8 import java.util.Set;
 9 import java.util.TreeMap;
10
11 import org.junit.Test;
12
13 public class TestCollection {
14
15     public static void print(Collection<? extends Object> c){
16         Iterator<? extends Object> it = c.iterator();
17         while (it.hasNext()) {
18             Object object = (Object) it.next();
19             System.out.println(object);
20         }
21     }
22
23     @Test
24     public void demo1(){
25         Set<String> set = new HashSet<String>();
26         set.add("AAA");
27         set.add("BBB");
28         set.add("CCC");
29         print(set);
30
31         //Set的第一种遍历方式:利用Iterator
32         Iterator<String> it1 = set.iterator();
33         for (String ss : set) {
34             System.out.println(ss);
35         }
36         //Set的第一种遍历方式:利用foreach
37         for (String sss : set) {
38             System.out.println(sss);
39         }
40
41
42         List<String> list = new ArrayList<String>();
43         list.add("DDDDD");
44         list.add("EEEEE");
45         list.add("FFFFF");
46         print(list);
47
48         //List的第一种遍历方式:因为list有顺序，利用size()和get()方法获取
49         for (int i = 0; i < list.size(); i++) {
50             System.out.println(list.get(i));
51         }
52         //List的第二种遍历方式：利用Iterator
53         Iterator<String> it = list.iterator();
54         while (it.hasNext()) {
55             System.out.println(it.next());
56         }
57         //List的第三种遍历方式:利用foreach
58         for (String s2 : list) {
59             System.out.println(s2);
60         }
61
62
63         Map<String,String> map = new TreeMap<String, String>();
64         map.put("Jerry", "10000");
65         map.put("shellway", "20000");
66         map.put("Kizi", "30000");
67         print(map.entrySet());
68         //Map的第一种遍历方式：先获得key,再获得值value
69         Set<String> sett = map.keySet();
70         for (String s : sett) {
71             System.out.println(s+":"+map.get(s));
72         }
73         //Map的第二种遍历方式：获得键值对
74         for (Map.Entry<String, String> entry : map.entrySet()) {
75             System.out.println(entry.getKey()+" : "+entry.getValue());
76         }
77     }
78 }

使用泛型对集合对象进行类型安全检查和遍历