JAVA中list,set,map与数组之间的转换详解

package test;

import java.util.*;

/**
 * Created by ming
 */
public class Test {

    public static void main(String[] args) {
        Set<Long> longSet=new HashSet<>();
        longSet.add(1L);
        longSet.add(2L);
        List<Long> longList=new ArrayList<>();
        longList.addAll(longSet);//list转set
        for(Long t : longList){
            System.out.println(t);
        }
        Set<Long> set2=new HashSet<>();
        set2.addAll(longList);//list转set
        for(Long s : set2){
            System.out.println(s);
        }
        Map<Long,Long> map=new HashMap<>();//list转map
        for(Long t : longList){
            map.put(t,t);
        }
        for(Long s : set2){//set转map
            System.out.println(s);
        }

        Collection<Long> collections= map.values();
        for (Long t : collections){
            System.out.println("map转集合"+t);
        }

        Long longs[]={2L,3L,4L};//定义一个数组
        List<Long> longList1 = Arrays.asList(longs);//数组转集合
        for(Long t : longList1){
            System.out.println("数组转集合"+t);
        }

       Long [] newLongs= longList1.toArray(new Long []{});
        System.out.println("集合转数组的方法:"+newLongs.length);

    }
}