What is the function of replaceFirst in Java?

In Java, the replaceFirst() method is used to replace the first matching substring in a string with a specified new string. Specifically, the replaceFirst() method takes two parameters: a regular expression to match the substring and a new string to replace it with. When the replaceFirst() method is called, it searches for the first substring that matches the regular expression in the string and replaces it with the specified new string. If no matching substring is found, the original string remains unchanged.