StringBuffer replace() Method in Java with Examples

The StringBuffer.replace() is the inbuilt method which is used to replace the characters in a substring of this sequence with the characters in the specified String. Here simply the characters in the substring are removed and other char is inserted at the start.
Syntax : 

public StringBuffer replace(int first, int last, String st)

Parameters : The method accepts three parameters. 

• first : This is of integer type which refers to the starting index.
• last : This is of integer type which refers to the ending index.
• st : This is of string type which refer to the String that will replace previous contents.

Return Value : The method returns this object after performing the above mentioned operations.
Exception : If the first is negative, greater than length(), or greater than last then StringIndexOutOfBoundsException.
Examples :

Input:
StringBuffer= "The first planet of solar system is merrhxy"
first = 39
last = 42
st = "cur"

Output: The first planet of solar system is mercury

Below programs illustrate the java.lang.StringBuffer.replace() method: 
Program 1: 

java

// Java program to illustrate the
// java.lang.StringBuffer.replace()

import java.lang.*;

public class Geeks {

    public static void main(String[] args)
    {

        StringBuffer sbf = new StringBuffer("Welcome to Geekshssgeeks");
        System.out.println("string buffer = " + sbf);

        // Replacing substring from index 15 to index 18
        sbf.replace(15, 18, "for");

        System.out.println("After replacing string buffer= " + sbf);
    }
}

Output:

string buffer = Welcome to Geekshssgeeks
After replacing string buffer= Welcome to Geekforsgeeks

Program 2: When negative index is passed: 

java

// Java program to illustrate the
// java.lang.StringBuffer.replace()

import java.lang.*;

public class Geeks {

    public static void main(String[] args)
    {

        StringBuffer sbf = new StringBuffer("Welcome to Geekshssgeeks");
        System.out.println("string buffer = " + sbf);

        // Replacing substring from index -15 to index -18
        sbf.replace(-15, -18, "for");

        System.out.println("After replacing string buffer= " + sbf);
    }
}

Output:

Exception in thread "main" java.lang.StringIndexOutOfBoundsException: 
String index out of range: -15
at java.lang.AbstractStringBuilder.replace(AbstractStringBuilder.java:851)
at java.lang.StringBuffer.replace(StringBuffer.java:452)
at Geeks.main(Geeks.java:14)

Program 3: When index passed is greater than length 

java

// Java program to illustrate the
// java.lang.StringBuffer.replace()

import java.lang.*;

public class Geeks {

    public static void main(String[] args)
    {

        StringBuffer sbf = new StringBuffer("Welcome to Geekshssgeeks");
        System.out.println("string buffer = " + sbf);

        // Replacing substring from index 215 to index 218
        sbf.replace(215, 218, "for");

        System.out.println("After replacing string buffer= " + sbf);
    }
}

Output:

Exception in thread "main" java.lang.StringIndexOutOfBoundsException: 
start > length()
at java.lang.AbstractStringBuilder.replace(AbstractStringBuilder.java:853)
at java.lang.StringBuffer.replace(StringBuffer.java:452)
at Geeks.main(Geeks.java:14)