Java String Methods – Developer Quick Reference

Why Master Java String Methods?

Strings are the backbone of most real-world software applications — used in user input validation, API communication, data parsing, and reporting. Mastering these core String methods helps developers write cleaner, more optimized, and reliable programs. Understanding how to efficiently manipulate and compare strings improves data accuracy and performance in every layer of enterprise software.

Core Java String Methods with Examples and Outputs

Method	Description	Example Code	Output
`length()`	Returns the number of characters in the string.	`System.out.println("Hello".length());`	5
`trim()`	Removes extra spaces from both ends of the string.	`System.out.println(" Java ".trim());`	Java
`substring(int start, int end)`	Extracts a substring between specified indexes.	`System.out.println("developer".substring(0, 3));`	dev
`regionMatches()`	Compares regions of two strings for equality.	`String a="ApplicationServer"; String b="ServerRoom"; System.out.println(a.regionMatches(11, b, 0, 6));`	true
`toLowerCase()`	Converts the string to all lowercase characters.	`System.out.println("HELLO".toLowerCase());`	hello
`toUpperCase()`	Converts the string to all uppercase characters.	`System.out.println("java".toUpperCase());`	JAVA
`indexOf()`	Returns the position of the first occurrence of a substring.	`System.out.println("technology".indexOf("nology"));`	4
`charAt()`	Returns the character at a specified index.	`System.out.println("Code".charAt(1));`	o
`concat()`	Joins two strings together.	`System.out.println("Java".concat("FX"));`	JavaFX
`equals()`	Checks if two strings are equal (case-sensitive).	`System.out.println("Java".equals("java"));`	false
`equalsIgnoreCase()`	Checks equality ignoring case differences.	`System.out.println("Admin".equalsIgnoreCase("admin"));`	true
`startsWith()`	Checks if the string starts with the given prefix.	`System.out.println("welcome".startsWith("wel"));`	true
`endsWith()`	Checks if the string ends with the given suffix.	`System.out.println("project.doc".endsWith(".doc"));`	true
`split()`	Splits a string into an array based on a delimiter.	`String[] arr="A,B,C".split(","); System.out.println(arr[1]);`	B
`join()`	Combines multiple strings with a specified separator.	`System.out.println(String.join("-", "2025", "10", "16"));`	2025-10-16