Strings in Java

String creation, common methods, immutability, StringBuilder, and StringBuffer in Java.

String Creation

String literal — String s = "Hello"; (stored in the string pool).
Using new — String s = new String("Hello"); (creates a new object on the heap).

Common String Methods

Method	Description
`length()`	Returns the number of characters
`charAt(i)`	Returns the character at index `i`
`concat(s)`	Concatenates another string
`substring(begin, end)`	Extracts a substring
`toUpperCase()`	Converts to uppercase
`toLowerCase()`	Converts to lowercase
`equals(s)`	Compares content for equality
`contains(s)`	Checks if string contains a sequence

String Immutability

Strings in Java are immutable — once created, their value cannot be changed. Every modification creates a new String object.

StringBuilder and StringBuffer

StringBuilder — Mutable string, not thread-safe, faster for single-threaded use.
StringBuffer — Mutable string, thread-safe (synchronized), slightly slower.

Example

// StringDemo.java
// Demonstrates string creation and common string methods in Java.

public class StringDemo {
	public static void main(String[] args) {
		// String creation using literal
		String s = "Hello";
		// Convert to uppercase
		System.out.println(s.toUpperCase());

		// String concatenation
		String s2 = s.concat(" World");
		System.out.println(s2);

		// StringBuilder for mutable strings
		StringBuilder sb = new StringBuilder("Java");
		sb.append(" Programming");
		System.out.println(sb);
	}
}

Full source: examples/08-strings/StringDemo.java