The String.replaceFirst(String regex, String replacement) method replaces the first substring of this string that matches the given regular expression with the given replacement.

Java String.replaceFirst() Method Example

This is a complete example to demonstrate the usage of replaceFirst()  methods.

public class ReplaceExample {
    public static void main(String[] args) {
        String str = "javaguides";
        String subStr = str.replaceFirst("[a-z]", "java");
        System.out.println(subStr);
    }
}

Output:

javaavaguides 

Reference

https://www.javaguides.net/2018/08/java-string-class-api-guide.html

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