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

  1 package com.example.test;
  2
  3 import java.util.ArrayList;
  4 import java.util.Arrays;
  5 import java.util.HashMap;
  6 import java.util.HashSet;
  7 import java.util.List;
  8 import java.util.Map;
  9 import java.util.Set;
 10
 11 public class ConvertorTest {
 12
 13     /**
 14      * @param args
 15      */
 16     public static void main(String[] args) {
 17
 18         testList2Array();
 19         testArray2List();
 20         testSet2List();
 21         testList2Set();
 22         testSet2Array();
 23         testArray2Set();
 24         testMap2Set();
 25         testMap2List();
 26     }
 27
 28     private static void testMap2List() {
 29
 30         Map<String, String> map = new HashMap<String, String>();
 31         map.put("A", "ABC");
 32         map.put("K", "KK");
 33         map.put("L", "LV");
 34
 35         // 将Map Key 转化为List
 36         List<String> mapKeyList = new ArrayList<String>(map.keySet());
 37         System.out.println("mapKeyList:"+mapKeyList);
 38
 39         // 将Map Key 转化为List
 40         List<String> mapValuesList = new ArrayList<String>(map.values());
 41         System.out.println("mapValuesList:"+mapValuesList);
 42
 43     }
 44
 45     private static void testMap2Set() {
 46
 47         Map<String, String> map = new HashMap<String, String>();
 48         map.put("A", "ABC");
 49         map.put("K", "KK");
 50         map.put("L", "LV");
 51
 52         // 将Map 的键转化为Set
 53         Set<String> mapKeySet = map.keySet();
 54         System.out.println("mapKeySet:"+mapKeySet);
 55
 56         // 将Map 的值转化为Set
 57         Set<String> mapValuesSet = new HashSet<String>(map.values());
 58         System.out.println("mapValuesSet:"+mapValuesSet);
 59     }
 60
 61     private static void testArray2Set() {
 62
 63         String[] arr = {"AA","BB","DD","CC","BB"};
 64
 65         //数组-->Set
 66         Set<String> set = new HashSet<String>(Arrays.asList(arr));
 67         System.out.println(set);
 68     }
 69
 70     private static void testSet2Array() {
 71         Set<String> set = new HashSet<String>();
 72         set.add("AA");
 73         set.add("BB");
 74         set.add("CC");
 75
 76         String[] arr = new String[set.size()];
 77         //Set-->数组
 78         set.toArray(arr);
 79         System.out.println(Arrays.toString(arr));
 80     }
 81
 82     private static void testList2Set() {
 83
 84         List<String> list = new ArrayList<String>();
 85         list.add("ABC");
 86         list.add("EFG");
 87         list.add("LMN");
 88         list.add("LMN");
 89
 90         //List-->Set
 91         Set<String> listSet = new HashSet<String>(list);
 92         System.out.println(listSet);
 93     }
 94
 95     private static void testSet2List() {
 96
 97         Set<String> set = new HashSet<String>();
 98         set.add("AA");
 99         set.add("BB");
100         set.add("CC");
101
102         //Set --> List
103         List<String> setList = new ArrayList<String>(set);
104         System.out.println(setList);
105     }
106
107     private static void testList2Array() {
108         //List-->数组
109         List<String> list = new ArrayList<String>();
110         list.add("AA");
111         list.add("BB");
112         list.add("CC");
113         Object[] objects = list.toArray();//返回Object数组
114         System.out.println("objects:"+Arrays.toString(objects));
115
116         String[] arr = new String[list.size()];
117         list.toArray(arr);//将转化后的数组放入已经创建好的对象中
118         System.out.println("strings1:"+Arrays.toString(arr));
119     }
120
121     private static void testArray2List() {
122         //数组-->List
123         String[] ss = {"JJ","KK"};
124         List<String> list1 = Arrays.asList(ss);
125         List<String> list2 = Arrays.asList("AAA","BBB");
126         System.out.println(list1);
127         System.out.println(list2);
128     }
129
130 }