Java Strings and String Methods - Detailed Guide

Basics of Java String

Java me String ek sequence of characters hota hai jo immutable hota hai. Matlab String create hone ke baad usme changes nahi kiye ja sakte. Strings string literals ya new keyword se banaye ja sakte hain.

String s1 = "Hello";
String s2 = new String("Hello");

String pool ki wajah se same literals ko memory me share kiya jata hai.

Common String Methods

Method	Description	Example	Return Type
`charAt(int index)`	Kisi specific index par character return kare	`s.charAt(0)`	char
`length()`	String ki length return kare	`s.length()`	int
`substring(int start, int end)`	Substring return kare starting index se end index tak	`s.substring(0, 3)`	String
`indexOf(String str)`	Substring ka first occurrence index return kare	`s.indexOf("lo")`	int
`toLowerCase()`	String ko lowercase me convert kare	`s.toLowerCase()`	String
`toUpperCase()`	String ko uppercase me convert kare	`s.toUpperCase()`	String
`trim()`	String ke dono taraf ke whitespace remove kare	`s.trim()`	String
`equals(String s2)`	Strings ko value-wise compare kare	`s.equals(s2)`	boolean
`equalsIgnoreCase(String s2)`	Case ignore karke strings compare kare	`s.equalsIgnoreCase(s2)`	boolean
`contains(CharSequence s)`	String ke andar substring present hai ya nahi check kare	`s.contains("ell")`	boolean
`replace(CharSequence target, CharSequence replacement)`	Substring replace kare	`s.replace("l", "r")`	String
`split(String regex)`	String ko given regex ke basis par split karke array banaye	`s.split(" ")`	String[]

String Methods - Examples

String s = "Hello World";
System.out.println("Length: " + s.length());
System.out.println("Char at 4: " + s.charAt(4));
System.out.println("Substring (0,5): " + s.substring(0, 5));
System.out.println("Index of \"World\": " + s.indexOf("World"));
System.out.println("Uppercase: " + s.toUpperCase());
System.out.println("Lowercase: " + s.toLowerCase());
System.out.println("Trimmed: " + "   Java   ".trim());
System.out.println("Contains \"lo\": " + s.contains("lo"));
System.out.println("Replace 'l' with 'x': " + s.replace("l", "x"));

String Immutability in Java

Java Strings immutable hote hain, iska matlab jab aap string par koi operation karte hain to nayi string create hoti hai, original string change nahi hoti. Yeh thread safety aur performance optimization mein madad karta hai.

String str = "Hello";
String newStr = str.replace("l", "p");
System.out.println(str);     // Output: Hello
System.out.println(newStr);  // Output: Heppo