I'm supposed to grab 4 strings from a scanner in my main method (s1, s2, s3, and s4-- the main method works perfectly after testing) and call this:

--> concat(s1, s2, s3, s4);

The method name, `concat`, is probably misleading, because I don't just want `s1+s2+s3+s4`. What I really need is to start with `s1`, and then add characters from `s2`, `s3` and `s4` that aren't already present in the result `String`. For example, if `s1` is "drain" and `s2` is "dane", the partial result after processing `s2` would be "draine" since the `d`, `a` and `n` are already present in the result `String`.

Here is the method:

```
public static void concat(String s1, String s2, String s3, String s4) {

      String str;
      StringBuilder createdWord = new StringBuilder();      

      for (int i = 0; i < s1.length(); i++) {
         char c = s1.charAt(i);
         for (int j = 0; j < createdWord.length(); j++) {
            if (createdWord.charAt(j) != c)
               createdWord.append(c);             
         }                  
      }

      for (int i = 0; i < s2.length(); i++) {
         char c = s2.charAt(i);
         for (int j = 0; j < createdWord.length(); j++) {
            if (createdWord.charAt(j) != c)
               createdWord.append(c);             
         }         
      }

      for (int i = 0; i < s3.length(); i++) {
         char c = s3.charAt(i);
         for (int j = 0; j < createdWord.length(); j++) {
            if (createdWord.charAt(j) != c)
               createdWord.append(c);             
         }         
      }

      for (int i = 0; i < s4.length(); i++) {
         char c = s4.charAt(i);
         for (int j = 0; j < createdWord.length(); j++) {
            if (createdWord.charAt(j) != c)
               createdWord.append(c);             
         }         
      }

      str = createdWord.toString();
      System.out.println(str);

   }

```

When I try to print (str), I get a blank output. I am positive that there's a way to make this simpler. 

I'll accept the answer based on clarity, simplicity, and/or an easier solution. Thanks in advance!