使用地图计算文本文件中出现的次数

Question

下面的代码将计算每个字符的出现次数。如果我在文本文件中有 abc 输出将是 a 1 b 1 c 1。我在许多网站上读到 for 循环将花费大量时间，最好使用哈希映射来实现相同的效果。你们中的任何人都可以帮我如何转换这个实现哈希映射的程序吗？

 import java.io.*;

    class Count_Char {
    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();
    for(int count =0;count<char_array.length;count++){
    char ch= char_array[count];
    int counter=0;
    for ( int i=0; i<char_array.length; i++){
    if (ch==char_array[i])
    counter++;
    }
    boolean flag=false;
    int j=count-1;
    while(j>=0)
        {

        if(ch==char_array[j])
            flag=true;
            j--;
        }
    if(!flag){
    System.out.println(ch+" "+counter);
    }
    }
        }catch(IOException e1){
            System.out.println(e1);
        }
        }
    }

Answer 1

快速伪代码。基本上，这里的技巧是将字符保存为映射中的键，值是该字符出现的次数（键/值对）。

 //declare a map to hold your characters and their counters
 Map<String,Integer> charCounter = new HashMap<String,Integer>();
 //the following if else logic goes when you are looping through your tokens
    if(charCounter.containsKey(<your character>)){
           charCounter.put(<your character>,charCounter.get(<your character>)+1);
    }else{
          charCounter.put(<your character>,1);
    }

遍历完成后，您可以通过这种方式打印地图。

for(String key : charCounter.keySet()) {
            System.out.println(key+" "+charCounter.get(key));
}

Answer 2

FileInputStream 文件 = new FileInputStream("");
DataInputStream dis = new DataInputStream(文件);
BufferedReader br = new BufferedReader(new InputStreamReader(dis));

        String temp="";
        Map<String,Integer> charCounter = new HashMap<String,Integer>();
      while ((temp=br.readLine()) != null)
      {
         String[] spliter= temp.split("");
         for(String temp1:spliter)
         if(charCounter.containsKey(temp1)){
               charCounter.put(temp1,charCounter.get(temp1)+1);
        }else{
              charCounter.put(temp1,1);
        }


      }


            System.out.println(charCounter);

建立在逻辑上，coolbean 已经写好了..希望这会有所帮助...我已经测试过这个..