java 集合转换(数组ListSetMap相互转换)

Posted 2020-11-04 lizggo

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);
}

}