In this section we will learn what the String replaceFirst() method is and how to use it in Java.

What is Java String replaceFirst() Method?

When we want to search in a string to find a substring and replace that substring with a new one, the `replaceFirst()` method is the way to go.

Note: this method only replaces the first occurrence of the substring that we’re looking for in the target string.

Java replaceFirst() Method Syntax:

public String replaceFirst(String regex, String replacement)

replaceFirst() Method Parameters:

• The first argument of the method is a regular expression that defines the substring that we’re looking for in the target string object.

Note: Other than regular expression, the first argument can also be a simple string word or sentence or even a letter. The point is the first argument is considered as the substring that the method should search for in the target string.

• The second argument is the substring that we want to be used as the replacement with the one that might be found in the target string.

Note: Please check the Regular Expression section if you don’t know what it is and how it works.

replaceFirst() Method Return Value:

The return value of this method is a new string value that contains the replaced substring.

Note: using this method won’t change the original string value.

replaceFirst() Method Exceptions:

This method does not throw an exception.

Example: using String replaceFirst() method

public class Simple {

    public static void main(String[] args)  {
        String w = "Goodbye World!";
        String res = w.replaceFirst("Goodbye", "Hello");
        System.out.println(res);
    }
}

Output:

Hello World!