Java: find common characters in two strings

Question

I'm asked to write a program that finds the common characters in two strings using the indexOf(char) method and a for loop. Here's what I have so far - the output comes out blank still.

import java.util.Scanner;
public class ClassName {
   public static void main (String args []) {

   Scanner input = new Scanner (System.in);

   String a = "";
   String b = "";
   String c = "";

   System.out.print("Enter two words: ")
   a = input.nextLine();
   b = input.nextLine();

   for (int i = 0; i < a; i++){

      char ch = a.charAt(i);
      if (b.indexOf(ch) != -1){
         c = c+String.valueOf(ch);
         }
      }
System.out.print("Common letters are: "+c);
}

}

output here

I'm not sure where to go from here.

thanks

Answer 1

Your code will duplicate common characters for example if you compare "developper" to "programmer" your result string will contain three time the e character

If you don't want that behaviour I suggest that you also use a Set like this:

public class CommonCharsFinder {

    static String findCommonChars(String a, String b) {
        StringBuilder resultBuilder = new StringBuilder();
        Set<Character> charsMap = new HashSet<Character>();
        for (int i = 0; i < a.length(); i++) {
            char ch = a.charAt(i); //a and b are the two words given by the user
             if (b.indexOf(ch) != -1){
                 charsMap.add(Character.valueOf(ch));
             }
        }

        Iterator<Character> charsIterator = charsMap.iterator();
        while(charsIterator.hasNext()) {
            resultBuilder.append(charsIterator.next().charValue());
        }
        return resultBuilder.toString();
    }
    // An illustration here
    public static void main(String[] args) {
       String s1 = "developper";
       String s2 = "programmer";

       String commons = findCommonChars(s1, s2);
       System.out.println(commons);     
    }

}

Result from the example: