리스트에서 객체 반복 횟수 [회전]를 집계하려면 JDK1이 필요합니다.5+

import java.util.ArrayList;  
import java.util.Collections;  
import java.util.HashMap;  
import java.util.HashSet;  
import java.util.List;  
import java.util.Map;  
import java.util.Set;  
import java.util.TreeMap;  
   
public class CountDuplicatedList {  
   
    public static void main(String[] args) {  
   
        List list = new ArrayList();  
        list.add("a");  
        list.add("b");  
        list.add("c");  
        list.add("d");  
        list.add("b");  
        list.add("c");  
        list.add("a");  
        list.add("a");  
        list.add("a");  
   
        System.out.println("
 1 -  'a' ");  
        System.out.println("a : " + Collections.frequency(list, "a"));  
   
        System.out.println("
 2 -  ");  
        Set uniqueSet = new HashSet(list);  
        for (String temp : uniqueSet) {  
            System.out.println(temp + ": " + Collections.frequency(list, temp));  
        }  
   
        System.out.println("
 3 - Map ");  
        Map map = new HashMap();  
   
        for (String temp : list) {  
            Integer count = map.get(temp);  
            map.put(temp, (count == null) ? 1 : count + 1);  
        }  
        printMap(map);  
   
        System.out.println("
Map - key ");  
        Map treeMap = new TreeMap(map);  
        printMap(treeMap);  
   
    }  
   
    public static void printMap(Map map) {  
        for (Map.Entry entry : map.entrySet()) {  
            System.out.println("Key-value : " + entry.getKey() + "- "  
                    + entry.getValue());  
        }  
    }  
}