Java String substring() Method Examples

Java String substring() method returns the substring of this string. This method always returns a new string and the original string remains unchanged because String is immutable in Java.

Java String substring() Methods

Java String substring method is overloaded and has two variants.

1. substring(int beginIndex): This method returns a new string that is a substring of this string. The substring begins with the character at the specified index and extends to the end of this string.
2. substring(int beginIndex, int endIndex): The substring begins at the specified beginIndex and extends to the character at index endIndex - 1. Thus the length of the substring is (endIndex - beginIndex).

String substring() Method Important Points

1. Both the string substring methods can throw IndexOutOfBoundsException if any of the below conditions met.
   • if the beginIndex is negative
   • endIndex is larger than the length of this String object
   • beginIndex is larger than endIndex
2. beginIndex is inclusive and endIndex is exclusive in both substring methods.

Java String substring() Example

Here is a simple program for the substring in java.

package com.journaldev.util;

public class StringSubstringExample {

	public static void main(String[] args) {
		String str = "www.journaldev.com";
		System.out.println("Last 4 char String: " + str.substring(str.length() - 4));
		System.out.println("First 4 char String: " + str.substring(0, 4));
		System.out.println("website name: " + str.substring(4, 14));
	}
}

Output of the above substring example program is:

Last 4 char String: .com
First 4 char String: www.
website name: journaldev

Checking Palindrome using substring() Method

We can use the substring() method to check if a String is a palindrome or not.

package com.journaldev.util;

public class StringPalindromeTest {
	public static void main(String[] args) {
		System.out.println(checkPalindrome("abcba"));
		System.out.println(checkPalindrome("XYyx"));
		System.out.println(checkPalindrome("871232178"));
		System.out.println(checkPalindrome("CCCCC"));
	}

	private static boolean checkPalindrome(String str) {
		if (str == null)
			return false;
		if (str.length() <= 1) {
			return true;
		}
		String first = str.substring(0, 1);
		String last = str.substring(str.length() - 1);
		if (!first.equals(last))
			return false;
		else
			return checkPalindrome(str.substring(1, str.length() - 1));
	}
}

Here we are checking if the first letter and the last letter is the same or not. If they are not the same, return false. Otherwise, call the method again recursively passing the substring with the first and last letter removed.

You can checkout more string examples from our GitHub Repository.

Reference: Oracle API Doc