Java 集合转换（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 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);
    }  

}