Java 集合转换(Object[]数组、List、Set、Map相互转换)

    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 value 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);    
        }  
      
    }