是什么导致数组越界错误，如何清除代码？

Question

This program is supposed to ascribe each letter of the alphabet its value in Scrable, take a text file, process the individual words, and print the word with the highest value average value (with the average value being the total value of all characters, letters and non-letters, divided by the number of those characters). My code seems almost complete but it reports an out of bounds error and I dont know why.

This is the error: java.lang.ArrayIndexOutOfBoundsException: -52

This is the class driver:

import java.util.Scanner;
import java.io.*;

public class ScrabbleDriver{
    public static void main(String[] args) throws IOException{
    try{
        Scanner scan = new Scanner(System.in);
        System.out.println("Enter text file ");
        String fileName = scan.next();
        Scrabble s = new Scrabble(fileName);
        s.readLines(); 
        s.report(); 
    }
    catch(Exception e){
        System.out.println(e);}
    }
}

This is the constructor class:

import java.io.IOException;
import java.util.StringTokenizer;

public class Scrabble extends Echo {

    private int [] scores = {1, 3, 3, 2, 1, 4, 2, 4, 1, 8, 5, 1, 3, 1, 1, 3, 10, 1, 1, 1, 1, 4, 4, 8, 4, 10};
    private double maxScore = 0;
    private String maxScoreWord = " ";

    public Scrabble(String fn) throws IOException {
        super(fn);
    }

    public void processLine(String line) {
        line = line.toLowerCase();
        StringTokenizer s = new StringTokenizer(line);
        while (s.hasMoreTokens()) {
            processToken(s.nextToken());
        }
    }

    public void processToken(String token) {
        double wordScore = 0;
        for (int n = 0 ; n < token.length() ; n++) {
            char j = token.charAt(n);
            if ((j == '!') || (j == ',') || (j == '.'))
                wordScore = wordScore;
            else {
                int m = (int) (j - 'a');
                if (m <= 25) {
                    wordScore = wordScore + scores[m];
                }
            }
        }
        wordScore = (wordScore / token.length());
        if (wordScore > maxScore) {
            maxScore = wordScore;
            maxScoreWord = token;
        }
    }

    public void report() {
        System.out.print("Winner: " + maxScoreWord + "   " + "Score: " + maxScore);
    }
}

This is Echo class:

import java.util.Scanner;
import java.io.*;

public class Echo {

    String fileName; // external file name
    Scanner scan; // Scanner object for reading from external file

    public Echo(String fn) throws IOException {
        fileName = fn;
        scan = new Scanner(new FileReader(fileName));
    }

    public void readLines() { // reads lines, hands each to processLine
        while (scan.hasNext()) {
            processLine(scan.nextLine());
        }
        scan.close();
    }

    public void processLine(String line) { // does the real processing work
        System.out.println(line);
    }
}

If any more info is needed, let me know.

Offending block

int m = (int)(j - 'a');
if(m <= 25){

wordScore = wordScore + scores[m];

}

Answer 1

Your error is in scores[m] . If you select an array position beyond the length (or less than) of scores , then you will get an Out of Bounds Exception. You need to check the length of your array first. The calculation j - 'a' is producing a negative number.

Finally, ensure that m is not less than zero. You are checking if it is less than 25.

Here is a link to an ASCII table . There are char less than 'a' in the table. Therefore, you need to adjust your logic.

Since you are only working with presumably lower case letters, you need to make sure that your character value is between 97 and 122 before subtracting. So, you can compare the letters by saying:

if (j < 'a' || j > 'z')
{
   continue;
}

Answer 2

Probably m is negative. You only test against 25 or less.

Try to make sure that j (why name it j ?) represents a letter before doing the calculation.

if (j < 'a' || j > 'z') {
    continue;
}

Or, alternatively, make sure that strange characters are not part of a "word" using the tokenizer. Depends on where you want to go with it.