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("\n例子 1 -統計'a'出現的頻率");
	System.out.println("a : " + Collections.frequency(list, "a"));
 
	System.out.println("\n例子 2 - 統計每一個元素出現的頻率");
	//將List轉換為Set
	Set uniqueSet = new HashSet(list);
	for (String temp : uniqueSet) {
		System.out.println(temp + ": " + Collections.frequency(list, temp));
	}
 
	System.out.println("\n例子 3 - 用Map統計每個元素出現的頻率");
	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("\nSorted Map");
	Map treeMap = new TreeMap(map);
	printMap(treeMap);
 
  }
 
  public static void printMap(Map map){
 
	for (Map.Entry entry : map.entrySet()) {
		System.out.println("Key : " + entry.getKey() + " Value : "
			+ entry.getValue());
	}
 
  }
 
}
 

	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("\n例子 1 -統計'a'出現的頻率");

	System.out.println("a : " + Collections.frequency(list, "a"));

	System.out.println("\n例子 2 - 統計每一個元素出現的頻率");

	//將List轉換為Set
 

	Set uniqueSet = new HashSet(list);
	for (String temp : uniqueSet) {
		System.out.println(temp + ": " + Collections.frequency(list, temp));
	}
 
	System.out.println("\n例子 3 - 用Map統計每個元素出現的頻率");
	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("\nSorted Map");
	Map treeMap = new TreeMap(map);
	printMap(treeMap);
 
  }
 
  public static void printMap(Map map){
 
	for (Map.Entry entry : map.entrySet()) {
		System.out.println("Key : " + entry.getKey() + " Value : "
			+ entry.getValue());
	}
 
  }
 
}
 

	for (String temp : uniqueSet) {

		System.out.println(temp + ": " + Collections.frequency(list, temp));

	}

	System.out.println("\n例子 3 - 用Map統計每個元素出現的頻率");

	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("\nSorted Map");
	Map treeMap = new TreeMap(map);
	printMap(treeMap);
 
  }
 
  public static void printMap(Map map){
 
	for (Map.Entry entry : map.entrySet()) {
		System.out.println("Key : " + entry.getKey() + " Value : "
			+ entry.getValue());
	}
 
  }
 
}

	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 treeMap = new TreeMap(map);
	printMap(treeMap);
 
  }
 
  public static void printMap(Map map){
 
	for (Map.Entry entry : map.entrySet()) {
		System.out.println("Key : " + entry.getKey() + " Value : "
			+ entry.getValue());
	}
 
  }
 
}

	printMap(treeMap);

  }

  public static void printMap(Map map){
 
	for (Map.Entry entry : map.entrySet()) {
		System.out.println("Key : " + entry.getKey() + " Value : "
			+ entry.getValue());
	}
 
  }
 
}

	for (Map.Entry entry : map.entrySet()) {
		System.out.println("Key : " + entry.getKey() + " Value : "
			+ entry.getValue());
	}
 
  }
 
}

		System.out.println("Key : " + entry.getKey() + " Value : "

			+ entry.getValue());

	}

  }

}

結果：

例子 1 -統計'a'出現的頻率

a : 4

例子 2 - 統計每一個元素出現的頻率

d: 1

b: 2

c: 2

a: 4

例子 3 - 用Map統計每個元素出現的頻率

Key : d Value : 1

Key : b Value : 2

Key : c Value : 2

Key : a Value : 4

Sorted Map

Key : a Value : 4

Key : b Value : 2

Key : c Value : 2

Key : d Value : 1