嵌套循环和数组（频率分析）

Question

I was wondering if I could get some help with with properly incrementing values to arrays. The point of this program is to analyze the frequency of individual letters in a text file, and record them in an array.

import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;
public class FrequencyAnaylsis 
{
public static String[] alphabet = {"a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z"};
public static int[] alphabetFrequency = new int[26];
public static int[] alphabetPercentage = new int[26];

FrequencyAnaylsis()
{
}

public static void getFileAndFrequency() throws FileNotFoundException
{
    File plaintext = new File("subplaintext");
    Scanner inFile = new Scanner(plaintext);

    for (int i = 0; i < 26; i++) //specifies the index of alphabet (the letter the program is looking for)
    {   
        while (inFile.hasNext()) //is true when the document has another word following the previous
        {
            String[] lettersToCompare = inFile.next().toLowerCase().split("(?!^)"); //splits the specified word into a String array

            for (int stringIndex = 0; stringIndex < lettersToCompare.length; stringIndex++) //loops through the index (individual letters) of the split word
            {
                if (lettersToCompare[stringIndex].equals(alphabet[i])) //if letter specified in split word equals letter specified in alphabet
                {
                    alphabetFrequency[i]++; //add one to the frequency array in the same index as the index in alphabet
                }
            }
        }   
    }
}

public static void getPercentage()
{
    int alphabetFrequencyTotal = 0;

    for (int i = 0; i < 26; i++)
    {
        alphabetFrequencyTotal =+ alphabetFrequency[i];
    }

    for (int i = 0; i < 26; i++)
    {
        alphabetPercentage[i] = alphabetFrequency[i]/alphabetFrequencyTotal;
    }
}

public static void printData()
{
    for (int i = 0; i < 26; i++)
    {
        System.out.println(alphabetFrequency[i]);
    }
}

public static void main(String[] args) throws FileNotFoundException
{
    FrequencyAnaylsis.getFileAndFrequency();
    //FrequencyAnaylsis.getPercentage();
    FrequencyAnaylsis.printData();

}
}

When the program reads this sentence: "Five score years ago, a great American, in whose symbolic shadow we stand, signed the Emancipation Proclamation.", it outputs the following:

12
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0

It's able to count the characters correctly in the case of "a", but it doesn't do so for any other letter. Why is that? Any help would be appreciated.

Answer 1

You problem is that you're trying to go through the file once for each letter of the English alphabet with this:

public static void getFileAndFrequency() throws FileNotFoundException
{
    File plaintext = new File("subplaintext");
    Scanner inFile = new Scanner(plaintext);

    for (int i = 0; i < 26; i++) //specifies the index of alphabet (the letter the program is looking for)
    {   
        while (inFile.hasNext()) //is true when the document has another word following the previous
        {
            String[] lettersToCompare = inFile.next().toLowerCase().split("(?!^)"); //splits the specified word into a String array

            for (int stringIndex = 0; stringIndex < lettersToCompare.length; stringIndex++) //loops through the index (individual letters) of the split word
            {
                if (lettersToCompare[stringIndex].equals(alphabet[i])) //if letter specified in split word equals letter specified in alphabet
                {
                    alphabetFrequency[i]++; //add one to the frequency array in the same index as the index in alphabet
                }
            }
        }   
    }
}

After the outer loop ( for (int i = 0; i < 26; i++) ) has run once, you're at the end of file, so all subsequent runs will act as though the file is empty.

A simple fix is to change the order of the loops:

public static void getFileAndFrequency() throws FileNotFoundException
{
    File plaintext = new File("subplaintext");
    Scanner inFile = new Scanner(plaintext);

    while (inFile.hasNext()) //is true when the document has another word following the previous
    {   
        String[] lettersToCompare = inFile.next().toLowerCase().split("(?!^)"); //splits the specified word into a String array

        for (int i = 0; i < 26; i++) //specifies the index of alphabet (the letter the program is looking for)
        {
            for (int stringIndex = 0; stringIndex < lettersToCompare.length; stringIndex++) //loops through the index (individual letters) of the split word
            {
                if (lettersToCompare[stringIndex].equals(alphabet[i])) //if letter specified in split word equals letter specified in alphabet
                {
                    alphabetFrequency[i]++; //add one to the frequency array in the same index as the index in alphabet
                }
            }
        }   
    }
}

However, you're doing way too much in the inner loop. As @Jägermeister points out, you'd be better off either using a Map (eg HashMap ) or utilize that you can simply assign the indices in your alphabetFrequency array directly:

public static void getFileAndFrequency() throws FileNotFoundException
{
    File plaintext = new File("subplaintext");
    Scanner inFile = new Scanner(plaintext);

    while (inFile.hasNext()) //is true when the document has another word following the previous
    {   
        String[] lettersToCompare = inFile.next().toLowerCase().split("(?!^)"); //splits the specified word into a String array

        for (int stringIndex = 0; stringIndex < lettersToCompare.length; stringIndex++) //loops through the index (individual letters) of the split word
        {
            char ch = lettersToCompare[stringIndex].charAt(0);
            if (ch >= 'a' && ch <= 'z')
                alphabetFrequency[ch-'a']++; //add one to the frequency array in the same index as the index in alphabet
        }   
    }
}

Example of using a Map :

public static Map<Char,Integer> getFileAndFrequency() throws FileNotFoundException
{
    Map<Char,Integer> frequencyMap = new HashMap<Char,Integer>();
    File plaintext = new File("subplaintext");
    Scanner inFile = new Scanner(plaintext);

    while (inFile.hasNext()) //is true when the document has another word following the previous
    {   
        String[] lettersToCompare = inFile.next().toLowerCase().split("(?!^)"); //splits the specified word into a String array

        for (int stringIndex = 0; stringIndex < lettersToCompare.length; stringIndex++) //loops through the index (individual letters) of the split word
        {
            char ch = lettersToCompare[stringIndex].charAt(0);
            Integer frequency = frequencyMap.get(ch);
            if (frequency ==null) {
               frequency = 0;
            }
            frequency += 1;
            frequencyMap.put(ch, frequency);
        }   
    }
    return frequencyMap;
}