Java Listで重複した項目を数える方法

package com.example;

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("\nExample 1 - Count 'a' with frequency");
    System.out.println("a : " + Collections.frequency(list, "a"));

    System.out.println("\nExample 2 - Count all with frequency");
    Set uniqueSet = new HashSet(list);
    for (String temp : uniqueSet) {
        System.out.println(temp + ": " + Collections.frequency(list, temp));
    }

    System.out.println("\nExample 3 - Count all with 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("\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());
    }

  }

}

Example 1 - Count 'a' with frequency
a : 4

Example 2 - Count all with frequency
d: 1
b: 2
c: 2
a: 4

Example 3 - Count all with Map
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