Limiting spaces in looped stringbuilder

Question

I'm stumped and have no idea how to do this. I'm creating a method that will take a String[] as an argument and build it into a string. Then my main method will use the output from this method as name for a fileWriter. The rest of the code is in place.

public static String nameFromString (String[] args){
    StringBuilder builder = new StringBuilder();
    for (int i = 1; i < args.length; i++) {
        builder.append(args[i]);
        builder.append(" ");
    }
    return builder.toString();  
}

If I, for example, write "new My File" in my program, it uses "My file" as a name and the main method appends a ".txt". So far, no problems.

But my problem, right now, is that it names the file "My File .txt" and also, when reading a file, using this same method, it tries to read "File name .txt" instead of "File name.txt".

How do I remove this last space in the string?

Answer 1

One way is to make the call to append conditional on the loop index:

for (int i = 1; i < args.length; i++) {
    builder.append(args[i]);
    if (i < args.length - 1) {
      builder.append(" ");
    }
}

Answer 2

You can use the String.trim() method to remove leading and trailing spaces.

String str = " ab c  ".trim(); // -> "ab c"

Answer 3

I see a lot of answers with index or buffer checking here. I just want to share a piece of code I use often and it is based on Guava Joiner class:

String result = Joiner.on(' ').join(args);

It is really small and clever solution from Google. Also it is optimized and uses StringBuilder inside..

Answer 4

You could use an "insert", or you could modify your append or you could trim() as follows

APPEND very similar to your initial just add the if.

if (i + 1 < args.length) { // added if.
  builder.append(" ");
}

"INSERT" change the loop a little

for (int i = 1; i < args.length; i++) {
  if (i != 1) {
    builder.append(" ");
  }
  builder.append(args[i]);
}

TRIM change the return like this

return builder.toString().trim();  

Answer 5

There are a number of ways this can be achieved. I use to delete the last character from the StringBuilder after the loop had completed, but this requires you to ensure that the last character is a space, instead, I know use...

for (int i = 1; i < args.length; i++) {
    if (builder.length() > 0) {
        builder.append(" ");
    }
    builder.append(args[i]);
}

Answer 6

The easiest is to append one string ahead and then continue just toggling the append sequence:

if(args.length < 2)return "";

StringBuilder builder = new StringBuilder(args[1]);

for (int i = 2; i < args.length; i++) {
        builder.append(" ");
        builder.append(args[i]);

    }

return builder.toString();