Introduction

Efficient string manipulation is a fundamental requirement in Java programming. Two commonly used classes, StringBuilder and StringBuffer, offer mutable sequences of characters, each with distinct characteristics. Understanding the differences between these two classes is crucial for writing performant and thread-safe Java applications.
This article provides an in-depth look at the differences between StringBuilder and StringBuffer in Java and explains when to use each one.

1. What Are StringBuilder vs StringBuffer in Java?

Both StringBuilder and StringBuffer in Java allow for the efficient creation and manipulation of strings, unlike the immutable String class. The StringBuffer class was introduced in Java 1.0, providing synchronized (thread-safe) string operations. Later, Java 5 introduced StringBuilder as a faster, unsynchronized alternative for single-threaded contexts.

2. Key Differences: StringBuilder vs StringBuffer in Java

While both classes serve similar purposes, their behavior in concurrent environments distinguishes them.

• Synchronization: StringBuffer is synchronized, ensuring thread safety. StringBuilder is not, thus offering higher performance but at the cost of thread safety.
• Performance: As a result of the absence of synchronization, StringBuilder is generally faster than StringBuffer.
• Compatibility: Methods and APIs are nearly identical, allowing easy migration from StringBuffer to StringBuilder when thread safety is unnecessary.

When performance is a priority and thread safety is not required, always prefer StringBuilder over StringBuffer in Java.

3. Creating Instances: StringBuilder vs StringBuffer in Java

Instantiating both classes is straightforward and follows similar patterns.

StringBuilder sb = new StringBuilder("Example");
StringBuffer sf = new StringBuffer("Example");

Description:
Both constructors above initialize the objects with the string "Example". You can also create empty instances or specify initial capacity. Because the APIs are nearly identical, switching between these classes is seamless.

4. Common Operations: StringBuilder vs StringBuffer in Java

You can perform various operations such as append, insert, delete, reverse, and toString with both classes. Each method behaves identically, aside from synchronization.

// StringBuilder example
StringBuilder sb = new StringBuilder("Java");
sb.append(" World");      // Adds " World"
sb.insert(4, " SE");      // Inserts " SE"
sb.delete(0, 5);          // Deletes first 5 chars
sb.reverse();             // Reverses the string
String resultSb = sb.toString();

// StringBuffer example
StringBuffer sf = new StringBuffer("Java");
sf.append(" World");      // Adds " World"
sf.insert(4, " SE");      // Inserts " SE"
sf.delete(0, 5);          // Deletes first 5 chars
sf.reverse();             // Reverses the string
String resultSf = sf.toString();

Description:
Both objects use the same method names and behaviors, making it simple for developers to switch between them depending on the need for synchronization.

If you wish to learn more about advanced string manipulation, check our tutorial on Advanced String Manipulation Recipes for Coding Interviews..

5. Performance: StringBuilder vs StringBuffer in Java

Performance is a primary consideration when deciding between StringBuilder and StringBuffer in Java. In single-threaded code, StringBuilder is faster since it does not incur synchronization overhead. In multi-threaded applications where the same instance is modified by multiple threads, StringBuffer ensures thread safety.

// Concatenating numbers from 1 to 10000
StringBuilder sbPerf = new StringBuilder();
for (int i = 0; i < 10000; i++) {
    sbPerf.append(i);
}
String strBuilder = sbPerf.toString();

StringBuffer sfPerf = new StringBuffer();
for (int i = 0; i < 10000; i++) {
    sfPerf.append(i);
}
String strBuffer = sfPerf.toString();

Description:
These code snippets demonstrate how both classes efficiently concatenate large numbers of strings, but StringBuilder performs better in environments without concurrency.

6. When to Use Each: Best Practices

Selecting between StringBuilder and StringBuffer in Java depends on your use case:

• Use StringBuilder in single-threaded code for maximum speed.
• Use StringBuffer only when thread safety is required.
• Avoid unnecessary synchronization, as it can degrade performance.

Choose StringBuilder for speed, but StringBuffer for thread safety.

Conclusion

Understanding the distinction between StringBuilder and StringBuffer in Java is vital for writing efficient, safe, and maintainable Java code. By choosing the appropriate class for your scenario, you ensure both correctness and optimal performance.
Continue exploring related topics, such as String Manipulation Recipes, and Advanced String Manipulation Recipes, to deepen your Java expertise.

You can find the complete code of this article on GitHub.