我需要打印文本文件中每个字母的频率。现在，我对如何将字母放入数组中感到困惑，因此它们用数字表示（a-0，b-1，c-2，d-3等）。那我该如何计算每个字母而又不单独计算每个字母。

样本输入（在文本文件中）：

我过得愉快。

样本输出（不包括省略号）：

a-3 b-0 c-0 d-3 ... 1一 1一 i-1 ... o-2 ... y-1 z-0

/*
 * program that reads in a text file and counts the frequency of each letter
 * displays the frequencies in descending order
 */

import java.util.*; //needed for Scanner
import java.io.*;  //needed for File related classes
public class LetterCounter {
  public static void main(String args[]) throws IOException{
    Scanner keyboard = new Scanner(System.in); //Scanner to read in file name
    System.out.println("Enter the name of the text file to read:");
    String filename = keyboard.next();

    //This String has all the letters of the alphabet
    //You can use it to "look up" a character using alphabet.indexOf(...) to see what letter it is
    //0 would indicate 'a',1 for 'b',and so on.  -1 would mean the character is not a letter
    String alphabet = "abcdefghijklmnopqrstuvwxyz";

    //TODO: create a way to keep track of the letter counts
    //I recommend an array of 26 int values,one for each letter,so 0 would be for 'a',etc.


    Scanner fileScan = new Scanner(new File(filename));  //another Scanner to open and read the file
    //loop to read file line-by-line
    while (fileScan.hasnext()) {  //this will continue to the end of the file
      String line = fileScan.nextLine();  //get the next line of text and store it in a temporary String
      line = line.toLowerCase( ); // convert to lowercase

      //TODO: count the letters in the current line


    }
    fileScan.close(); //done with file reading...close the Scanner so the file is "closed"



    //print out frequencies
    System.out.println("Letters - Frequencies in file:");

    //TODO: print out all the letter counts


  }
}