Java StringBuffer replace() method - Replaces the characters in a substring of this sequence with characters in the specified String. The substring begins at the specified start and extends to the character at index end - 1 or to the end of the sequence if no such character exists. First, the characters in the substring are removed and then the specified String is inserted at the start. (This sequence will be lengthened to accommodate the specified String if necessary.)

Java StringBuffer replace() Example

Example: Example to replace string "ja" with string "java" using replace() method.

public class ReplaceExample {
    public static void main(String[] args) {
        StringBuffer buffer = new StringBuffer("jaguides");
  
        // replace ja with java- start index 0 and end index -1
        StringBuffer subBuffer = buffer.replace(0, 2, "java");
  
        System.out.println(subBuffer);
    }
}

Output:

javaguides

Reference

https://www.javaguides.net/2018/08/stringbuffer-class-methods-in-java.html