Java - remove middle part of a string

Question

I want the following output for the following input:

input: adele
output: ae

Code:

public class delDel {
    public static String delDel(String str) {
        StringBuilder sb = new StringBuilder();
        if(str.length() < 3){
           return str;
        }
        else if(str.substring(1, 3).equals("del")){
            StringBuilder afterRemove = sb.delete(1, 3);
            return afterRemove.toString();
        }
        else{
           return str;
        }

   }

   public static void main(String[] args) {
      Scanner input = new Scanner(System.in);

      String yourStr = input.nextLine();

      System.out.println(delDel(yourStr));
   }
}

But I keep getting the same input.

Try some System.out.println to debug specially inside the else if.... do you arrive... what is inside of sb there is something? You will save a lot of time if you learn some simple debugging techniques — Petter Friberg
– Petter Friberg, Commented Nov 28, 2015 at 18:03

Tunaki · Accepted Answer · 2015-11-28 18:15:11Z

6

There are multiple problems here:

Your StringBuilder isn't initialized with the input String. It should be StringBuilder sb = new StringBuilder(str); As such, it is always empty.
substring and delete methods work with the last index exclusive, not inclusive. So to take a substring of length 3 starting at index 1, you need to call str.substring(1, 4).

Corrected code:

public static String delDel(String str) {
    StringBuilder sb = new StringBuilder(str);
    if(str.length() < 3){
       return str;
    }
    else if(str.substring(1, 4).equals("del")){
        StringBuilder afterRemove = sb.delete(1, 4);
        return afterRemove.toString();
    }
    else{
       return str;
    }
}

Side-note: since you are only using the StringBuilder in one case, you could move its declaration inside the else if (this way, you won't create a useless object when the String is less than 3 characters).

edited Nov 28, 2015 at 18:15

answered Nov 28, 2015 at 18:05

Tunaki

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3 Comments

Petter Friberg Over a year ago

If you give him the code, why not try to improve it some es. 1 check length before StringBuilder, 2 why create afterRemove, ecc.. remove all else if else since it has return values.... will your at it teach him some nice code style..

Tunaki Over a year ago

@PetterFriberg I agree about point 1 (and hesitated to add it before you pointed it) but I think point 2 doesn't apply: for a beginner, I feel it is easier to read code like this than a long line chaining calls like new StringBuilder(str).delete(1, 4).toString();

azurefrog Over a year ago

Not just for a beginner. I often create "unnecessary" interim variables solely to make it more clear at a glance what the code is supposed to do.

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