---
title: "Strings in Java"
description: 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

```java
// 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`](https://github.com/University-Of-Sri-Jayewardenepura/Java/blob/main/examples/08-strings/StringDemo.java)