CountLettersInArray.java

package chapter_seven.samples;

/**
 * Listing 7.4 CountLettersInArray.java
 */
public class CountLettersInArray
{
    /**
     * Main method
     */
    public static void main(String[] args)
    {
        // Declare and create an array
        char[] chars = createArray();

        // Display the array
        System.out.println("The lowercase letters are:");
        displayArray(chars);
        // Count the occurrences of each letter
        int[] counts = countLetters(chars);

        // Display counts
        System.out.println();
        System.out.println("The occurrences of each letter are:");
        displayCounts(counts);
    }

    /**
     * Create an array of characters
     */
    public static char[] createArray()
    {
        // Declare an array of characters and create it
        char[] chars = new char[100];

        // Create lowercase letters randomly and assign
        // them to the array
        for (int i = 0; i < chars.length; i++)
            chars[i] = RandomCharacter.getRandomLowerCaseLetter(); // RandomCharacter is Unknown

        // Return the array
        return chars;
    }

    /**
     * Display the array of characters
     */
    public static void displayArray(char[] chars)
    {
        // Display the characters in the array 20 on each line
        for (int i = 0; i < chars.length; i++)
        {
            if ((i + 1) % 20 == 0)
                System.out.println(chars[i]);
            else
                System.out.print(chars[i] + " ");
        }
    }

    /**
     * Count the occurrences of each letter
     */
    public static int[] countLetters(char[] chars)
    {
        // Declare and create an array of 26 int
        int[] counts = new int[26];

        // For each lowercase letter in the array, count it
        for (int i = 0; i < chars.length; i++)
            counts[chars[i] - 'a']++;

        return counts;
    }

    /**
     * Display counts
     */
    public static void displayCounts(int[] counts)
    {
        for (int i = 0; i < counts.length; i++)
        {
            if ((i + 1) % 10 == 0)
                System.out.println(counts[i] + " " + (char) (i + 'a'));
            else
                System.out.print(counts[i] + " " + (char) (i + 'a') + " ");
        }
    }
}