java - String replace method is not replacing characters

Question

I have a sentence that is passed in as a string and I am doing a replace on the word "and" and I want to replace it with " ". And it's not replacing the word "and" with white space. Below is an example of my logic. And when I debug this the logic does fall into the sentence.replace.

String sentence = "Define, Measure, Analyze, Design and Verify"
if (sentence.contains("and")){
    sentence.replace("and", " ");
}

Is there something I am missing here.

Answer 1

And when I debug this the logic does fall into the sentence.replace.

Yes, and then you discard the return value.

Strings in Java are immutable - when you call replace, it doesn't change the contents of the existing string - it returns a new string with the modifications. So you want:

sentence = sentence.replace("and", " ");

This applies to all the methods in String (substring, toLowerCase etc). None of them change the contents of the string.

Note that you don't really need to do this in a condition - after all, if the sentence doesn't contain "and", it does no harm to perform the replacement:

String sentence = "Define, Measure, Analyze, Design and Verify";
sentence = sentence.replace("and", " ");