Question

I am working on a homework assignment for a class and I have solved almost all of it, but am struggling with one part.

For the assignment, we are supposed to write a program that will count the frequency of occurrence of letters in any given string and then print out a map of them to the console. I have written the program and it works almost correctly, but I cannot get the map to ignore whitespace. It seems to find two different kinds of whitespace as well, one that is the space between words and another that I cannot figure out.

I’ve tried myString.replaceAll(" ", ""); and myString.trim(); to try and eliminate the whitespace before counting the frequency of letters, but it still counts both types of whitespace each time.

Any insight or help is appreciated. I could turn it in like this, but I don’t like half-assing projects. Here is the code:

import java.util.*;

public class LetterFrequency {
   public static void main( String[] args ) {

      Map< String, Integer > myMap = new HashMap< String, Integer >(); 

      createMap( myMap ); 
      displayMap( myMap );
   } 


   private static void createMap( Map< String, Integer > map ) {
      Scanner scanner = new Scanner( System.in ); 
      System.out.println( "Enter a string:" ); 
      String input = scanner.nextLine();

      System.out.println("String: "+input);

      String[] tokens = input.split("");


      for ( String token : tokens ) {
         String letter = token.toLowerCase();


         if ( map.containsKey( letter ) ) {
            int count = map.get( letter ); 
            map.put( letter, count + 1 );
         }
         else 
            map.put( letter, 1 );
      } 
   } 


   private static void displayMap( Map< String, Integer > map ) {      
      Set< String > keys = map.keySet(); 


      TreeSet< String > sortedKeys = new TreeSet< String >( keys );

      System.out.println( "\nMap contains:\nKey\t\tValue" );


      for ( String key : sortedKeys )
         System.out.printf( "%-10s%10s\n", key, map.get( key ) );

      System.out.printf( 
         "\nsize: %d\nisEmpty: %b\n", map.size(), map.isEmpty() );
   }
}

Answer 1

String.replaceAll should work. Keep in mind that String.replaceAll returns a String. So you have to use the string it returns to perform the rest of your computation.

For instance, if you have:

String myString = "hello world";
myString.replaceAll(" ", "");

myString will still be “hello world”

You’d want:

String myNewString = myString.replaceAll(" ", "");

After which myNewString will have no spaces.

Also, you can simplify your character iteration by using

for (int i = 0; i < input.length(); i++){
    char letter = input.charAt(i); 

This will fix your additional “whitespace being counted” problem. This is because when you call myString.split(""), the first element in the returned list is “” (an empty string).