Java代码如何对列表(重复项)进行分组计数呢?

实现思路:
    使用Collections.frequency方法
	即可计算出单个元素的个数

package com.java265;

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<String> list = new ArrayList<String>();
	list.add("java265.com");
	list.add("b");
	list.add("c");
	list.add("d");
	list.add("b");
	list.add("c");
	list.add("java265.com");
	list.add("java265.com");
	list.add("java265.com");
 
	System.out.println("\nExample 1 - Count 'a' with frequency");
	System.out.println("a : " + Collections.frequency(list, "java265.com"));
 
	System.out.println("\nExample 2 - Count all with frequency");
	Set<String> uniqueSet = new HashSet<String>(list);
	for (String temp : uniqueSet) {
		System.out.println(temp + ": " + Collections.frequency(list, temp));
	}
 
	System.out.println("\nExample 3 - Count all with Map");
	Map<String, Integer> map = new HashMap<String, Integer>();
 
	for (String temp : list) {
		Integer count = map.get(temp);
		map.put(temp, (count == null) ? 1 : count + 1);
	}
	printMap(map);
				
	System.out.println("\nSorted Map");
	Map<String, Integer> treeMap = new TreeMap<String, Integer>(map);
	printMap(treeMap);
		
  }
	
  public static void printMap(Map<String, Integer> map){
 
	for (Map.Entry<String, Integer> entry : map.entrySet()) {
		System.out.println("Key : " + entry.getKey() + " Value : "
			+ entry.getValue());
	}
		
  }
 
}