String class vs StringBuffer class in Java: Learn and Understand Differences, Performance, and Use Cases

String class vs StringBuilder class in Java: Learn Understand Differences, Performance, and Use Cases

1. Understanding String: Immutable and Constant

In Java, String is an immutable class, which means once created, its value cannot be changed. Every modification results in a new object, which can affect performance during frequent changes.

Example:

String str = "Hello";
str = str + " World"; // Creates a new String object

When to Use:

• When working with constant values.

• When thread safety is not a concern.

• When performance is not critical for string manipulation.

2. StringBuilder: Mutable and High Performance

StringBuilder is a mutable class introduced in Java 1.5. It allows modification of character sequences without creating new objects, making it efficient for multiple changes.

Example:

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

When to Use:

• When you need to build strings dynamically.

• In single-threaded applications for better performance.

• During loops or string concatenation inside algorithms.

3. StringBuffer: Thread-Safe but Slower

StringBuffer is similar to StringBuilder, but it is synchronized, making it thread-safe. However, the synchronization adds overhead and slows down performance compared to StringBuilder.

Example:

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

When to Use:

• In multi-threaded applications where multiple threads access the same buffer.

• When thread safety is a requirement.

• For legacy code written before Java 1.5.

4. Performance Comparison: Which is Faster?

Operation	String	StringBuilder	StringBuffer
Mutability	Immutable	Mutable	Mutable
Thread-safe	No	No	Yes
Performance	Slow	Fast (best)	Moderate (slower)
Use Case	Constants	Dynamic strings	Thread-safe cases

Benchmark Tip:

Using String in a loop for concatenation can drastically reduce performance. Prefer StringBuilder for fast string appending.

5. Best Practices: When to Use What?

• ✅ Use String for fixed, readable text like messages, labels, and keys.

• ✅ Use StringBuilder for high-performance string concatenation in loops and file parsing.

• ✅ Use StringBuffer if you are sharing string data between threads.

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