java中Array Set List互转问题

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);  
    }

}

注意：Set中放对象的时候，如果在for循环中声明new一个对象后进行赋值，执行set.add()方法的时候，Set集合中还是会有重复值。解决：对象必须在for循环外声明new，在循环内赋值，这样才能保证Set的不重复性。