Java Example - Collection Traversal

Traversal of List and Set type collections

1  import java.util.ArrayList;
 2  import java.util.HashSet;
 3  import java.util.Iterator;
 4  import java.util.List;
 5  import java.util.Set;
 6   
7  public  class Main {
 8   
9     public  static  void main(String[] args) {
 10        // Traversal of List collection 
11        listTest();
 12        // Traversal of Set collection 
13        setTest();
 14     }
 15   
16     private  static  void setTest() {
17       Set<String> set = new HashSet<String>();
18       set.add("JAVA");
19       set.add("C");
20       set.add("C++");
21       // 重复数据添加失败
22       set.add("JAVA");
23       set.add("JAVASCRIPT");
24  
25       // 使用iterator遍历set集合
26       Iterator<String> it = set.iterator();
27       while (it.hasNext()) {
28          String value = it.next();
29          System.out.println(value);
30       }
31       
32       // 使用增强for循环遍历set集合
33       for(String s: set){
34          System.out.println(s);
35       }
36    }
37  
38    // 遍历list集合
39    private static void listTest() {
40       List<String> list = new ArrayList<String>();
41       list.add("W");
42       list.add("M");
43       list.add("L");
44       list.add("D");
45       list.add("www.pekst.com");
46  
47       // 使用iterator遍历
48       Iterator<String> it = list.iterator();
49       while (it.hasNext()) {
50          String value = it.next();
51          System.out.println(value);
52       }
53  
54       // 使用传统for循环进行遍历
55       for (int i = 0, size = list.size(); i < size; i++) {
56          String value = list.get(i);
57          System.out.println(value);
 58        }
 59   
60        // Use enhanced for loop to traverse 
61        for (String value : list) {
 62           System.out.println(value);
 63        }
 64     }
 65 }

Traversal of Map type collections

In the following example we use the keySet() and entrySet() methods of HashMap to traverse the collection:

1  import java.util.Map;
 2  import java.util.HashMap;
 3  import java.util.HashSet;
 4  import java.util.Iterator;
 5  import java.util.List;
 6  import java.util.Set;
 7  import java.util.Map.Entry;
 8  
9  // Enhanced For loop 
10  public  class Main {
 11  
12     public  static  void main(String[] args) {
 13        // Create a HashMap object and add some key-value pairs. 
14        Map<String, String> maps =new HashMap<String, String> ();
 15        maps.put("1", "PHP" );
 16        maps.put("2", "Java" );
 17        maps.put("3", "C" );
 18        maps.put("4", "C++" );
 19        maps.put("5", "HTML" );
 20        
21        // traditional method 1 of traversing the map set; keySet()
 22        // traditionalMethod1 (maps);
 23        // Traditional method 2 of traversing map collection; entrySet()
 24        // traditionalMethod2(maps);
 25        // Using enhanced For loop to traverse map collection method 1;
keySet()
26       //strongForMethod1(maps);
27       // 使用增强For循环来遍历map集合方法2; entrySet()
28       strongForMethod2(maps);
29    }
30 
31    private static void strongForMethod2(Map<String, String> maps) {
32       Set<Entry<String, String>> set = maps.entrySet();
33       for (Entry<String, String> entry : set) {
34          String key = entry.getKey();
35          String value = entry.getValue();
36          System.out.println(key + " : " + value);
37       }
38    }
39 
40     private  static  void strongForMethod1(Map<String, String> maps) {
 41        Set<String> set = maps.keySet();
 42        for (String s : set) {
 43           String key = s;
 44           String value = maps.get (s);
 45           System.out.println(key + " : " + value);
 46        }
 47     }
 48  
49     // Use the entrySet() method to get each key-value pair in the maps collection, 
50     private  static  void traditionalMethod2 (Map<String, String> maps) {
 51       Set<Map.Entry<String, String>> sets = maps.entrySet();
 52        // Get the iterator to traverse the corresponding value. 
53        Iterator<Entry<String, String>> it = sets.iterator();
 54        while (it.hasNext()) {
 55           Map.Entry<String, String> entry = (Entry<String, String> ) it.next ();
 56           String key = entry.getKey();
 57           String value = entry.getValue();
 58           System.out.println(key + " : " + value);
 59        }
 60     }
 61  
62     // Use keySet( ) method to get all the keys in the maps collection, traverse the keys to get the corresponding values.
63    private static void traditionalMethod1(Map<String, String> maps) {
64       Set<String> sets = maps.keySet();
65       // 取得迭代器遍历出对应的值
66       Iterator<String> it = sets.iterator();
67       while (it.hasNext()) {
68          String key = it.next();
69          String value = maps.get(key);
70          System.out.println(key + " : " + value);
71       }
72    }
73 }