Java 集合转换(数组、List、Set、Map相互转换)

转自：http://blog.csdn.net/top_code/article/details/10552827

 package com.example.test;

 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;

 public class ConvertorTest {

     /**
      * @param args
      */
     public static void main(String[] args) {

         testList2Array();
         testArray2List();
         testSet2List();
         testList2Set();
         testSet2Array();
         testArray2Set();
         testMap2Set();
         testMap2List();
     }

     private static void testMap2List() {

         Map<String, String> map = new HashMap<String, String>();
         map.put("A", "ABC");
         map.put("K", "KK");
         map.put("L", "LV");  

         // 将Map Key 转化为List
         List<String> mapKeyList = new ArrayList<String>(map.keySet());
         System.out.println("mapKeyList:"+mapKeyList);

         // 将Map Key 转化为List
         List<String> mapValuesList = new ArrayList<String>(map.values());
         System.out.println("mapValuesList:"+mapValuesList);

     }

     private static void testMap2Set() {

         Map<String, String> map = new HashMap<String, String>();
         map.put("A", "ABC");
         map.put("K", "KK");
         map.put("L", "LV");  

         // 将Map 的键转化为Set
         Set<String> mapKeySet = map.keySet();
         System.out.println("mapKeySet:"+mapKeySet);

         // 将Map 的值转化为Set
         Set<String> mapValuesSet = new HashSet<String>(map.values());
         System.out.println("mapValuesSet:"+mapValuesSet);
     }

     private static void testArray2Set() {

         String[] arr = {"AA","BB","DD","CC","BB"};  

         //数组-->Set
         Set<String> set = new HashSet<String>(Arrays.asList(arr));
         System.out.println(set);
     }

     private static void testSet2Array() {
         Set<String> set = new HashSet<String>();
         set.add("AA");
         set.add("BB");
         set.add("CC");

         String[] arr = new String[set.size()];
         //Set-->数组
         set.toArray(arr);
         System.out.println(Arrays.toString(arr));
     }

     private static void testList2Set() {

         List<String> list = new ArrayList<String>();
         list.add("ABC");
         list.add("EFG");
         list.add("LMN");
         list.add("LMN");

         //List-->Set
         Set<String> listSet = new HashSet<String>(list);
         System.out.println(listSet);
     }

     private static void testSet2List() {

         Set<String> set = new HashSet<String>();
         set.add("AA");
         set.add("BB");
         set.add("CC");

         //Set --> List
         List<String> setList = new ArrayList<String>(set);
         System.out.println(setList);
     }

     private static void testList2Array() {
         //List-->数组
         List<String> list = new ArrayList<String>();
         list.add("AA");
         list.add("BB");
         list.add("CC");
         Object[] objects = list.toArray();//返回Object数组
         System.out.println("objects:"+Arrays.toString(objects));  

         String[] arr = new String[list.size()];
         list.toArray(arr);//将转化后的数组放入已经创建好的对象中
         System.out.println("strings1:"+Arrays.toString(arr));
     }

     private static void testArray2List() {
         //数组-->List
         String[] ss = {"JJ","KK"};
         List<String> list1 = Arrays.asList(ss);
         List<String> list2 = Arrays.asList("AAA","BBB");
         System.out.println(list1);
         System.out.println(list2);
     }

 }