Java StringBuilder replace()

In this tutorial, we will discuss Java StringBuilder replace() method with the help of examples.

Syntax of replace() method:

//replace substring from index 4 to 9 by given string "hello"
//4 is inclusive and 9 is exclusive
sb.replace(4, 9, "hello");

replace() Description

public StringBuilder replace(int start, int end, String str): Replace the substring starting from start index till end index with the given string str.

replace() Parameters

The replace() method of Java StringBuilder class takes three parameters:

• start: Represents the start of substring that is going to be replaced.
• end: Represents the end of the substring that is going to be replaced.
• str: This string is going to replace the substring marked by start and end index.

replace Return Value

• Returns a StringBuilder object that contains the new string after replacement.

This method throws StringIndexOutOfBounds Exception, if any of the following condition occurs:

• start index < 0
• start index > length of the string

Example 1: Replacing a substring with another string

public class JavaExample {
  public static void main(String[] args) {
    StringBuilder sb = new StringBuilder("Hello Guys");
    System.out.println("Given String : "+sb);

    //replace the substring
    sb.replace(6, 10, "Friends");
    System.out.println("String after replace: "+sb);
  }
} 

Output:

Example 2: When replace string is greater than original string

public class JavaExample {
  public static void main(String[] args) {
    StringBuilder sb = new StringBuilder("Text");
    System.out.println("Given String: "+sb);
    //replace string is greater than original string
    sb.replace(0, 4, "AnotherText");
    System.out.println("String after replace: "+sb);
  }
} 

Output:

Example 3: When end index is greater than the length of string

public class JavaExample {
  public static void main(String[] args) {
    StringBuilder sb = new StringBuilder("Hello");
    System.out.println("Given String: "+sb);
    //end index is greater than original string length
    sb.replace(0, 100, "Hi");
    System.out.println("String after replace: "+sb);
  }
} 

Output:

Example 4: when start index is negative

public class JavaExample {
  public static void main(String[] args) {
    StringBuilder sb = new StringBuilder("Text");
    //start index is negative
    sb.replace(-5, 10, "AnotherText");
    System.out.println("String after replace: "+sb);
  }
} 

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