📘 Top 500 Java Interview Questions (With Topics)

🔍 Difference Between String, StringBuffer, and StringBuilder in Java

When working with text data in Java, developers often encounter three important classes: String, StringBuffer, and StringBuilder. Though they seem similar, they behave differently in terms of memory usage, performance, and thread safety.

📌 1. What is String?

String is an immutable class in Java. This means once a string object is created, it cannot be changed.

String s = "Hello";
s = s + " World";
System.out.println(s); // Output: Hello World

✅ Key Points:

• Immutable
• Thread-safe
• Not suitable for frequent modifications

📌 2. What is StringBuffer?

StringBuffer is a mutable class and thread-safe (synchronized). It allows modification of content without creating new objects.

StringBuffer sb = new StringBuffer("Hello");
sb.append(" World");
System.out.println(sb); // Output: Hello World

✅ Key Points:

• Mutable
• Thread-safe (synchronized)
• Slower than StringBuilder

📌 3. What is StringBuilder?

StringBuilder is similar to StringBuffer, but it's not thread-safe. It's faster and preferred for single-threaded applications.

StringBuilder sb = new StringBuilder("Hello");
sb.append(" World");
System.out.println(sb); // Output: Hello World

✅ Key Points:

• Mutable
• Not thread-safe
• Faster than StringBuffer

🔄 Comparison Table

Feature	String	StringBuffer	StringBuilder
Mutability	Immutable	Mutable	Mutable
Thread-safe	Yes	Yes	No
Performance	Slowest	Medium	Fastest
Synchronization	Not needed	Yes	No
Use Case	Fixed text	Multi-threaded	Single-threaded

🎯 Conclusion

Understanding the differences between these three classes is essential for writing optimized and clean Java code.

• Use String when the text won't change.
• Use StringBuffer in multi-threaded applications.
• Use StringBuilder for high-performance, single-threaded text manipulation.

Written by: Rehan Khan