Question

Basically given an int, I need to generate a String with the same length containing only the specified character. Related question here, but it relates to C# and it does matter what’s in the String.

This question, and my answer to it are why I am asking this one. I’m not sure what’s the best way to go about it performance wise.

Example

Method signature:

String getPattern(int length, char character);

Usage:

//returns "zzzzzz"
getPattern(6, 'z');

What I’ve tried

String getPattern(int length, char character) {
    String result = "";
    for (int i = 0; i < length; i++) {
        result += character;
    }
    return result;
}

Is this the best that I can do performance-wise?

Answer 1

You should use StringBuilder instead of concatenating chars this way. Use StringBuilder.append().

StringBuilder will give you better performance. The problem with concatenation the way you are doing is each time a new String (string is immutable) is created then the old string is copied, the new string is appended, and the old String is thrown away. It’s a lot of extra work that over a period of type (like in a big for loop) will cause performance degradation.