【转】Java集合间的相互转换-白红宇

【转】Java集合间的相互转换

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发布时间：2019-06-19

本文共 1750 字，大约阅读时间需要 5 分钟。

下面代码演示了List<-->数组、List<-->Set、数组<-->Set、Map将键转化为Set、Map将值转化为Set、Map将值转化为List等集合常用转化操作。

public class TestApp {    public static void main(String[] args) {        //List-->数组        List
     
       list = new ArrayList
      
       ();        list.add("蹇伟");        list.add("Jerval");        list.add("杰威");        Object[] objects = list.toArray();//返回Object数组        System.out.println("objects:"+Arrays.toString(objects));        String[] strings1 = new String[list.size()];        list.toArray(strings1);//将转化后的数组放入已经创建好的对象中        System.out.println("strings1:"+Arrays.toString(strings1));        String[] strings2 = list.toArray(new String[0]);//将转化后的数组赋给新对象        System.out.println("strings2:"+Arrays.toString(strings2));        //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);        //List-->Set        List
         
           list3 = new ArrayList
          
           (new HashSet
           
            ()); //Set-->List Set
            
              set = new HashSet
             
              (new ArrayList
              
               ()); //数组-->Set String[] strs = {"AA","BB"}; Set
               
                 set2 = new HashSet
                
                 (Arrays.asList(strs)); System.out.println(set2); //Set-->数组 Set
                 
                   set3 = new HashSet
                  
                   (Arrays.asList("PP","OO")); String[] strSet = new String[set3.size()]; set3.toArray(strSet); System.out.println(Arrays.toString(strSet)); //Map操作 Map
                   
                     map = new HashMap
                    
                     (); map.put("YYY", "UUU"); map.put("RRR", "TTT"); // 将键转化为Set Set
                     
                       mapKeySet = map.keySet(); // 将值转化为Set Set
                      
                        mapValuesSet = new HashSet
                       
                        (map.values()); // 将值转化为List List
                        
                          mapValuesList = new ArrayList
                         
                          (map.values()); }}