Java 集合转换(数组、List、Set、Map相互转换)

比眉伴天荒 2022-06-04 02:27 378阅读 0赞

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);  
     } }