? Java StringBuilder

? Quick Overview

StringBuilder is a mutable sequence of characters in Java. Unlike String, it allows modification of content without creating new objects, making it faster and memory-efficient.

? Key Concepts

Mutable string class
Located in java.lang package
Not thread-safe (faster than StringBuffer)
Used for frequent string modifications

? Syntax / Theory

A StringBuilder object can grow or shrink dynamically. Common operations include append(), insert(), delete(), and reverse().

? Code Example

? View Code Example

// Demonstrates basic StringBuilder operations
public class Main {
public static void main(String[] args) {
StringBuilder sb = new StringBuilder("Hello");
sb.append(" World");
sb.insert(5, ",");
sb.replace(0, 5, "Hi");
System.out.println(sb.toString());
}
}

? Live Output / Explanation

Output

Hi, World

The original string is modified directly without creating multiple objects, which improves performance.

? Interactive Playground

Simulate basic StringBuilder operations below:

"Start"

StringBuilder sb = new StringBuilder("Start");

✅ Tips & Best Practices

Use StringBuilder for heavy string concatenation
Avoid using it in multi-threaded environments
Convert to String only when final output is needed

? Try It Yourself

Create a StringBuilder and reverse a sentence
Build a string using a loop with append()
Compare performance with String concatenation