Java Example - Collection Traversal

The following example demonstrates how to traverse a collection of List, Set and Map types that are stored in the form of key-value pairs extended from the Collection interface. Below we use ordinary for, enhanced for, iterator and other methods to traverse. Collections:

Traversal of List and Set type collections

/*
 author by w3cschool.cc
 Main.java
 */import java.util.ArrayList;import java.util.HashSet;
 import java.util.Iterator;
 import java.util.List;import java.util.Set;
 public class Main {

   public static void main(String[] args) {
      // List集合的遍历
      listTest();
      // Set集合的遍历
      setTest();
   }

   private static void setTest() {
      Set<String> set = new HashSet<String>();
      set.add("JAVA");
      set.add("C");
      set.add("C++");
      // 重复数据添加失败
      set.add("JAVA");
      set.add("JAVASCRIPT");

      // 使用iterator遍历set集合
      Iterator<String> it = set.iterator();
      while (it.hasNext()) {
         String value = it.next();
         System.out.println(value);
      }
      
      // 使用增强for循环遍历set集合
      for(String s: set){
         System.out.println(s);
      }
   }

   // 遍历list集合
   private static void listTest() {
      List<String> list = new ArrayList<String>();
      list.add("菜");
      list.add("鸟");
      list.add("教");
      list.add("程");
      list.add("www.w3cschool.cc");

      // 使用iterator遍历
      Iterator<String> it = list.iterator();
      while (it.hasNext()) {
         String value = it.next();
         System.out.println(value);
      }

      // 使用传统for循环进行遍历
      for (int i = 0, size = list.size(); i < size; i++) {
         String value = list.get(i);
         System.out.println(value);
      }

      // 使用增强for循环进行遍历
      for (String value : list) {
         System.out.println(value);
      }
   }}

The output result of running the above code is:

菜鸟教程www.w3cschool.cc菜鸟教程www.w3cschool.cc菜鸟教程www.w3cschool.cc
JAVA
JAVASCRIPT
C++C
JAVA
JAVASCRIPT
C++C

About traversal of Map type collections

The following examples We used the keySet() and entrySet() methods of HashMap to traverse the collection:

/*
 author by w3cschool.cc
 Main.java
 */import java.util.Map;import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Iterator;import java.util.List;import java.util.Set;
 import java.util.Map.Entry;//增强For循环public class Main {

   public static void main(String[] args) {
      // 创建一个HashMap对象,并加入了一些键值对。
      Map<String, String> maps = new HashMap<String, String>();
      maps.put("1", "PHP");
      maps.put("2", "Java");
      maps.put("3", "C");
      maps.put("4", "C++");
      maps.put("5", "HTML");
      
      // 传统的遍历map集合的方法1; keySet()
      //traditionalMethod1(maps);
      // 传统的遍历map集合的方法2; entrySet()
      //traditionalMethod2(maps);
      // 使用增强For循环来遍历map集合方法1; keySet()
      //strongForMethod1(maps);
      // 使用增强For循环来遍历map集合方法2; entrySet()
      strongForMethod2(maps);
   }

   private static void strongForMethod2(Map<String, String> maps) {
      Set<Entry<String, String>> set = maps.entrySet();
      for (Entry<String, String> entry : set) {
         String key = entry.getKey();
         String value = entry.getValue();
         System.out.println(key + " : " + value);
      }
   }

   private static void strongForMethod1(Map<String, String> maps) {
      Set<String> set = maps.keySet();
      for (String s : set) {
         String key = s;
         String value = maps.get(s);
         System.out.println(key + " : " + value);
      }
   }

   // 使用entrySet()方法，获取maps集合中的每一个键值对，
   private static void traditionalMethod2(Map<String, String> maps) {
      Set<Map.Entry<String, String>> sets = maps.entrySet();
      // 取得迭代器遍历出对应的值。
      Iterator<Entry<String, String>> it = sets.iterator();
      while (it.hasNext()) {
         Map.Entry<String, String> entry = (Entry<String, String>) it.next();
         String key = entry.getKey();
         String value = entry.getValue();
         System.out.println(key + " : " + value);
      }
   }

   // 使用keySet()方法，获取maps集合中的所有键，遍历键取得所对应的值。
   private static void traditionalMethod1(Map<String, String> maps) {
      Set<String> sets = maps.keySet();
      // 取得迭代器遍历出对应的值
      Iterator<String> it = sets.iterator();
      while (it.hasNext()) {
         String key = it.next();
         String value = maps.get(key);
         System.out.println(key + " : " + value);
      }
   }}

The output result of running the above code is:

1 : PHP
2 : Java
3 : C
4 : C++
5 : HTML

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