HashMap按value的顺序输出

如果是要按照key的顺序排列的话 用TreeSet 按顺序输出就可以了,如果要按照value的顺序输出就麻烦一点点

先要得到value的list 用collections的sort方法来排序 然后安装list的顺序来输出

e.g.:

import java.io.*;
import java.util.*;
import java.util.Map.Entry;

/**
 * Created by Void Young on 8:53 PM 7/16/2016 .
 * IDEA-Test .
 * 统计一个文件内每个字符的出现次数把结果输出到一个文件中
 */
public class CountChar {
    public static void main (String[] args) throws IOException {
//        deom1 ();
        HashMap<Character, Integer> hm = new HashMap<> ();//这个是按照出现频率DESC的输出
        try(
                BufferedReader br = new BufferedReader (new FileReader ("z:/a.txt"))
        ) {
            String s;
            char c;
            while (( s = br.readLine () ) != null) {
                for (int i = 0; i < s.length (); i++) {
                    c = s.charAt (i);
                    hm.put (c, hm.containsKey (c) ? hm.get (c) + 1 : 1);
                }
            }
        }
        Set<Entry<Character,Integer>> set = hm.entrySet ();                                         //得到Entry的Set
        ArrayList<Entry<Character, Integer>> list = new ArrayList<> ();                        //建立一个List排序
        list.addAll (set);//装入Set的全部元素
        Collections.sort (list, new Comparator<Entry<Character, Integer>> () {      //自定义Comparator进行排序
            @Override
            public int compare (Entry<Character, Integer> o1, Entry<Character, Integer> o2) {
                return o2.getValue ()-o1.getValue ();//出现次数多的放前面
            }
        });
        try(
                BufferedWriter bw = new BufferedWriter (new FileWriter ("z:/2.txt"))
        ) {
            for (int i = 0; i < list.size (); i++) {//遍历List 输出到文件中
                Entry<Character, Integer> characterIntegerEntry = list.get (i);
                bw.write (characterIntegerEntry.getKey ()+" : "+characterIntegerEntry.getValue ());
                bw.newLine ();
            }
        }
    }

例子里面我提取出HashMap的EntrySet 放入一个List中,对這个List进行自定义Comparator安装value降序排序,然后遍历这个list 输出.从而得到按value降序的结果存入文件中.