statistics.java

用JAVA编写的小的JAVA程序,是有关密码转换的.有2种算法.

import java.io.FileReader;
import java.io.IOException;

/**
 * Counts the letters of a given text file.
 * The letters are restricted to a-z, A-Z, 0-9 and SPACE 
 */
public class Statistics {

    /**
     * Counts the letters.
     * 
     * @param filename The name of the textfile
     * @return An array of int with the number for each letters
     */
	
	// Space for 26 characters, 10 numbers and SPACE
	static int INDEX_ENTRIES=37;

	// Index 0-25 for "A-Z" (ASCII 65-90) and "a-z (ASCII 97-122)" ,
	static int UPPER_A_ASCII=Character.getNumericValue('A');
	static int LOWER_A_ASCII=Character.getNumericValue('a');
	static int A_INDEX=0;

	static int UPPER_Z_ASCII=Character.getNumericValue('Z');
	static int LOWER_Z_ASCII=Character.getNumericValue('z');
	static int Z_INDEX=25;

    // Index 26-35 for "0-9" (ASCII 48-57)
	static int ZERO_ASCII=Character.getNumericValue('0');
	static int ZERO_INDEX=26;

	static int NINE_ASCII=Character.getNumericValue('9');
	static int NINE_INDEX=35;

    // Index 36 for SPACE (ASCII 32)
	static int SPACE_ASCII=Character.getNumericValue(' ');
	static int SPACE_INDEX=36;
	
	
    public static int[] getStatistics(String filename) {

        // little helper
        int actChar=0;

        int[] stat = new int[INDEX_ENTRIES];

        try {
            //Open FileReader stream
            FileReader fr = new FileReader(filename);

            //Read each char until the stream is empty
            while ((actChar = fr.read()) != -1) {
                if (actChar == SPACE_ASCII)
                    stat[SPACE_INDEX]++; // SPACE
                else if (actChar >= ZERO_ASCII && actChar <= NINE_ASCII) {
                    stat[actChar + Z_INDEX - ZERO_ASCII]++; // Number!
                } else if (actChar >= UPPER_A_ASCII && actChar <= UPPER_Z_ASCII) {
                    stat[actChar - UPPER_A_ASCII]++; // Uppercase letters!
                } else if (actChar >= LOWER_A_ASCII && actChar <= LOWER_Z_ASCII) {
                    stat[actChar - LOWER_A_ASCII]++; // Lowercase letters!
                }
            }
            
            // Close the stream
            fr.close();
        } catch (IOException io) {
            io.printStackTrace();
            System.err.println("Error opening file " + filename);
        }

        return stat;
    }

// -------------

       
    /**
     * Prints out an array with the information of counted letters.
     * 
     * @param stats The array of statistics.
     */
    private static void printResults(int[] stats) {
        int actChar;

        // Only print those chars with hits
        for (int i = A_INDEX; i < Z_INDEX; i++) {
            if (stats[i] > 0) {
                actChar = i + LOWER_A_ASCII + 87;//XXX was ist das f黵 ne zahl?
                System.out.println((char) actChar + " = " + stats[i] + ", ");
            }
        }

        // same for numbers...
        for (int i = ZERO_INDEX; i < NINE_INDEX; i++)
            if (stats[i] > 0) {
                actChar = i - Z_INDEX;
                System.out.println(actChar + " = " + stats[i] + ", ");
            }

        // any spaces?
        if (stats[SPACE_INDEX] > 0)
            System.out.println("SPACE = " + stats[SPACE_INDEX]);
    }

//  -------------
    
    public static void main(String[] args) {

        if (args.length > 0)
            printResults(getStatistics(args[0]));
        else
            throw new IllegalArgumentException(
                    "No Filename given! Don't know what to parse!");

    }
}