List、Set、Map集合的相互转换

今天药忘吃喽~ 2021-08-30 21:00 527阅读 0赞

【一】List转Set

>     Set set=new HashSet(new ArrayList());

举例：

package convert;
    
    import java.util.*;
    
    public class ListToSet {
        public static void main(String[] args) {
            List<String> list=new ArrayList<>();
            list.add("001");
            list.add("qq1");
            list.add("ppkckd");
            list.add("12");
            list.add("12");
            list.add("qq1");
            
            //遍历List集合
            for(int i=0;i<list.size();i++){
                System.out.println(list.get(i));
            }
            System.out.println("=========================");
            //遍历set
            Set set=listToSet(list);
            Iterator it=set.iterator();
            while(it.hasNext()){
                System.out.println(it.next());
            }
            
        }
        public static Set listToSet(List list){
            Set set=new HashSet(list);
            return set;
        }
    }

输出：

001  
qq1  
ppkckd  
12  
12  
qq1  
=========================  
qq1  
001  
12  
ppkckd

【二】Set转List

> List list=new ArrayList<>(new HashSet);

package convert;
    
    import java.util.ArrayList;
    import java.util.HashSet;
    import java.util.List;
    import java.util.Set;
    
    public class SetToList {
        public static void main(String[] args) {
            Set<String> set=new HashSet<>();
            set.add("AAA");
            set.add("BBB");
            set.add("CCC");
            set.add("AAA");
    
            List<String> list=new ArrayList<>(set);
           
            System.out.println(list);
            
        }
    }

【三】Map转List

>     List mapKeyList = new ArrayList(map.keySet());
>     List mapValuesList = new ArrayList(map.values());

package convert;
    
    import java.util.ArrayList;
    import java.util.HashMap;
    import java.util.List;
    import java.util.Map;
    
    public class MapToList {
        public static void main(String[] args) {
            Map<String, String> map = new HashMap<String, String>();
            map.put("1", "ABC");
            map.put("2", "KK");
            map.put("3", "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);
        }
    }

【四】map转Set

>     Set<String> setKey=map.keySet();
>     Set<String> setValue=new HashSet<>(map.values());

package convert;
    
    import java.util.HashMap;
    import java.util.HashSet;
    import java.util.Map;
    import java.util.Set;
    
    public class MapToSet {
        public static void main(String[] args) {
            Map<String, String> map = new HashMap<String, String>();
            map.put("1", "ABC");
            map.put("2", "KK");
            map.put("3", "LV");
    
            Set<String> setKey=map.keySet();
            System.out.println(setKey);
            
            Set<String> setValue=new HashSet<>(map.values());
            System.out.println(setValue);
        }
    }