BeginnersBook

Java StringBuilder substring()

By Chaitanya Singh | Filed Under: java

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

The syntax of substring() method is:

sb.substring(4) //substring starting from index 4 till end
sb.substring(2, 5) //substring from index 2 till index 5

Here, sb is an object of StringBuilder class.

substring() Description

There are two variations of substring() method in Java StringBuilder class.

public String substring(int startIndex): It returns a substring starting from the specified index startIndex till the end of the given character sequence.

public String substring(int startIndex, int endIndex): It returns a substring starting from the specified index startIndex till the specified index endIndex.

substring() Parameters

It can take upto two parameters. The endIndex parameter is optional.

  • startIndex: Specifies the start position of the substring
  • endIndex: Specifies the end of the substring

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

  • If startIndex < 0 or >= length of the string represented by StringBuilder.
  • If endIndex < 0 or >= length of the string.
  • if startIndex > endIndex.

substring() Return Value

Returns a substring based on the specified indexes.

Example 1: When only startIndex is specified

class JavaExample{
  public static void main(String[] args) {
    StringBuilder sb = new StringBuilder("BeginnersBook");
    //substring begins from index 9
    String subStr = sb.substring(9);
    System.out.println("Substring from index 9: "+subStr);
  }
}

Output:

StringBuilder substring method output1

Example 2: When both startIndex and endIndex are specified

class JavaExample{
  public static void main(String[] args) {
    StringBuilder sb = new StringBuilder("BeginnersBook");
    //substring from 0 till 5
    String subStr = sb.substring(0, 5);
    System.out.println("Substring from index 0 to 5: "+subStr);
  }
}

Output:

StringBuilder substring method output2

Example 3: When startIndex is greater than endIndex

class JavaExample{
  public static void main(String[] args) {
    StringBuilder sb = new StringBuilder("BeginnersBook");
    //when startIndex is greater than endIndex
    String subStr = sb.substring(5, 2);
    System.out.println("Substring: "+subStr);
  }
}

Output:

StringBuilder substring method output3

Similarly, if any of the specified indexes are negative or >= to the string length then the method will throw this exception.