Java 集合转换(数组、List、Set、Map相互转换)

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    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);            }      }
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