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 map = new HashMap();  
        map.put("A", "ABC");  
        map.put("K", "KK");  
        map.put("L", "LV");  
        
		// 将Map Key 转化为List    
        List mapKeyList = new ArrayList(map.keySet());  
        System.out.println("mapKeyList:"+mapKeyList);
        
        // 将Map Key 转化为List    
        List mapValuesList = new ArrayList(map.values());  
        System.out.println("mapValuesList:"+mapValuesList);
        
	}

	private static void testMap2Set() {
		
        Map map = new HashMap();  
        map.put("A", "ABC");  
        map.put("K", "KK");  
        map.put("L", "LV");  
        
        // 将Map 的键转化为Set    
        Set mapKeySet = map.keySet();  
        System.out.println("mapKeySet:"+mapKeySet);
        
        // 将Map 的值转化为Set    
        Set mapValuesSet = new HashSet(map.values());  
        System.out.println("mapValuesSet:"+mapValuesSet);
	}

	private static void testArray2Set() {
		
        String[] arr = {"AA","BB","DD","CC","BB"};  
        
        //数组-->Set  
        Set set = new HashSet(Arrays.asList(arr));  
        System.out.println(set);  
	}

	private static void testSet2Array() {
		Set set = new HashSet();
		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 list = new ArrayList();
		list.add("ABC");
		list.add("EFG");
		list.add("LMN");
		list.add("LMN");
		
		//List-->Set
        Set listSet = new HashSet(list);
        System.out.println(listSet);
	}

	private static void testSet2List() {
		 
		Set set = new HashSet();
		set.add("AA");
		set.add("BB");
		set.add("CC");
		
		//Set --> List
        List setList = new ArrayList(set);
        System.out.println(setList);  
	}

	private static void testList2Array() {
		//List-->数组  
        List list = new ArrayList();  
        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 list1 = Arrays.asList(ss);  
        List list2 = Arrays.asList("AAA","BBB");  
        System.out.println(list1);  
        System.out.println(list2);  
	}

}