Hashmap实现计算每个字符的出现次数

Question

下面的代码是计算每个字符的出现次数,它应该打印计数.但是使用我试过的代码我只得到1我不知道我应该做的改变.请帮我.

import java.io.BufferedReader;
import java.io.DataInputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.HashMap;
import java.util.Map;

class Count_CharMap {
public static void main(String[] args) {
    try
    {
        FileInputStream file = new FileInputStream("D:\\trial.txt");
        DataInputStream dis = new DataInputStream(file);
        BufferedReader br = new BufferedReader(new InputStreamReader(dis));
        String Contents="";
        String str="";

        while ((Contents = br.readLine()) != null) {
            str+=Contents;
        }

        char[]char_array =str.toCharArray();
        int count = 0;
        char ch = char_array[count];
        Map<Character,Integer> charCounter=new HashMap<Character,Integer>();
        for(int i=0;i<str.length();i++)
        {
            if(charCounter.containsKey(char_array[i]))
            {
                charCounter.put(ch, charCounter.get(ch)+1);
            } 
            else
            {
                charCounter.put(ch, 1);
            }
       }

       for(Character key:charCounter.keySet())
       {
           System.out.println(key+""+charCounter.get(key));
       }
    } 
    catch(IOException e1){
        System.out.println(e1);
    }
    }
}

实际输出应该是如果我在我的trial.txt中有abcdabc它应该打印2 b 2c 2 d 1.

Answer 1

通过每次执行循环,您将char ch设置为相同的字符.

它应该是:

ch = char_array[i]; 
if(charCounter.containsKey(ch)){
     charCounter.put(ch, charCounter.get(ch)+1);
}
else
{
    charCounter.put(ch, 1);
}

在for循环中.

Answer 2

Java 8流：

Map<String, Long> map = 
    Arrays.stream(string.split("")).
    collect(Collectors.groupingBy(c -> c, Collectors.counting()));

番石榴HashMultiset：

Multiset<Character> set = HashMultiset.create(Chars.asList("bbc".toCharArray()));
assertEquals(2, set.count('b'));