HashMap按value的顺序输出 - 黑马程序员技术交流社区

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

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 ();
}
}
}

复制代码

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.