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

红太狼 2022-05-26 10:38 327阅读 0赞

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);    
            }  
          
        }