StringBuffer vs StringBuilder in Java: Key Differences Explained

In Java, handling and modifying strings is a common task. While the String class is immutable, Java provides two alternatives i.e., StringBuffer and StringBuilder to create and modify strings without creating new objects each time.

These two classes look similar, but they behave differently in multi-threaded environments. Choosing the right one impacts your program's performance and thread safety.

This blog explains the difference between StringBuffer and StringBuilder in Java, their syntax, use cases, conversions, and more. By the end, you’ll know when and why to use each of them effectively.

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StringBuffer vs StringBuilder in Java: Difference Table

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StringBuffer Class

StringBuffer in Java is a mutable class that allows you to modify the string without creating a new object. It is thread-safe, meaning multiple threads can access it without causing data corruption. All public methods of StringBuffer are synchronized, which ensures thread safety.

Syntax

StringBuffer sb = new StringBuffer("Hello");

Example

public class BufferExample {
    public static void main(String[] args) {
        StringBuffer sb = new StringBuffer("Java");
        sb.append(" Programming");
        System.out.println(sb);
    }
}

Output

Java Programming

Explanation

Here, we used append() to add content to the original string. Since StringBuffer is mutable, it updated the same object without creating a new one.

Also explore: Thread in Java – Complete Beginner’s Guide with Examples

StringBuilder Class

StringBuilder is similar to StringBuffer but faster because it is not synchronized. It is best suited for single-threaded applications where thread safety is not a concern. It provides the same methods and behavior as StringBuffer, except thread safety.

Syntax

StringBuilder sb = new StringBuilder("Hello");

Example

public class BuilderExample {
    public static void main(String[] args) {
        StringBuilder sb = new StringBuilder("Java");
        sb.append(" Developer");
        System.out.println(sb);
    }
}

Output

Java Developer

Explanation

The append() method added new content to the existing string. Since the class is not synchronized, it works faster but should not be used in multi-threaded programs.

Must read: Strings in Java vs Strings in C++: Key Differences Explained

Conversion from StringBuffer to StringBuilder

You can convert a StringBuffer object to StringBuilder by first converting it into a String, then passing it to the StringBuilder constructor. This is helpful when you want better performance in single-threaded scenarios.

Example

public class ConvertToBuilder {
    public static void main(String[] args) {
        StringBuffer buffer = new StringBuffer("Learn Java");
        StringBuilder builder = new StringBuilder(buffer.toString());
        System.out.println(builder);
    }
}

Output

Learn Java

Explanation

We used the toString() method to convert StringBuffer into String and then passed it to StringBuilder. This gives us a new, mutable, and faster object.

Also check: String Pool in Java: Concept, Working, Examples, and Use Cases

Conversion from StringBuilder to StringBuffer

To convert a StringBuilder to StringBuffer, convert it to a String first and then pass it to the StringBuffer constructor. Use this when moving from a non-thread-safe environment to a thread-safe one.

Example

public class ConvertToBuffer {
    public static void main(String[] args) {
        StringBuilder builder = new StringBuilder("Java Rocks");
        StringBuffer buffer = new StringBuffer(builder.toString());
        System.out.println(buffer);
    }
}

Output

Java Rocks

Explanation

The toString() method converted the StringBuilder to a String, which we used to initialize a new StringBuffer object. This ensures thread safety moving forward.

Must read: String Array in Java: A Complete Beginner’s Guide

Difference Between StringBuffer and StringBuilder

Here are the key differences between StringBuffer and StringBuilder:

• Thread Safety: StringBuffer is synchronized and thread-safe, whereas StringBuilder is not synchronized, hence not thread-safe.
• Performance: StringBuffer is slower due to synchronization overhead, while StringBuilder offers better performance in single-threaded operations.
• Introduced In: StringBuffer was introduced in Java 1.0, whereas StringBuilder came later in Java 5 for performance improvement.
• Use Case: Use StringBuffer for thread-safe applications, whereas StringBuilder suits high-performance, single-threaded environments.
• Mutability: Both StringBuffer and StringBuilder are mutable, allowing modification of content without creating new objects.
• Methods Available: Both provide similar methods like append(), insert(), and reverse() for efficient string operations.
• Package: Both classes belong to the java.lang package and don’t require any explicit import in Java programs.

Also explore: How to Convert String to int in Java: Methods and Examples

Conclusion

Both StringBuffer and StringBuilder are powerful tools for handling strings in Java. Choose StringBuffer when working in multi-threaded environments, and prefer StringBuilder for faster execution in single-threaded programs. Understanding these differences helps write more efficient and reliable Java code.

FAQs

1. Why is StringBuilder faster than StringBuffer?

StringBuilder is faster because it is not synchronized, meaning multiple threads can access it without blocking. This reduces overhead and improves performance in single-threaded environments, making it the preferred choice when thread safety is not a concern.

2. In which scenarios should you use StringBuffer over StringBuilder?

Use StringBuffer when multiple threads access and modify the same string object, and data consistency is critical. Its methods are synchronized, which ensures thread safety, making it suitable for multi-threaded applications that require shared access to string operations.

3. Can we use StringBuilder in multi-threaded programs?

You can use StringBuilder in multi-threaded programs only if there’s no shared access to the same object. If multiple threads modify the same instance, it can lead to inconsistent results. In such cases, prefer StringBuffer for safe execution.

4. Are methods in StringBuffer and StringBuilder exactly the same?

Yes, both classes share the same method signatures, such as append(), insert(), delete(), and reverse(). The core difference lies in synchronization. StringBuffer is thread-safe; StringBuilder is not, but they function identically otherwise.

5. How does StringBuilder differ from String in terms of memory?

StringBuilder creates a mutable sequence of characters, avoiding new object creation with each modification. In contrast, String is immutable, and any change creates a new object, which can increase memory usage and affect performance when making many modifications.

6. What happens if you use StringBuffer in a single-threaded application?

Using StringBuffer in a single-threaded application will still work, but it's less efficient. The synchronization adds unnecessary overhead, slowing down execution. In such cases, StringBuilder is a better choice for optimal performance without compromising output.

7. Is StringBuffer truly thread-safe in all cases?

StringBuffer is thread-safe because all its methods are synchronized. However, if the logic around StringBuffer is flawed or other objects are accessed unsafely, thread issues can still occur. Proper synchronization at the application level is still important.

8. Can StringBuilder and StringBuffer be converted back to String?

Yes, both classes provide a .toString() method that converts their contents to a standard immutable String object. This is useful when you’ve completed all modifications and need a regular String for further operations or return values.

9. Does StringBuilder or StringBuffer support method chaining?

Yes, both classes support method chaining. Since methods like append(), insert(), and delete() return the same object, you can chain multiple calls in a single statement, improving readability and reducing the need for multiple lines of code.

10. Are there any thread-safe alternatives to StringBuilder besides StringBuffer?

Yes, StringBuilder can be made thread-safe by manually synchronizing blocks or wrapping it with synchronization logic. Additionally, third-party libraries or using StringBuffer itself are viable options, depending on the level of thread safety required.

11. What is the default capacity of StringBuilder and StringBuffer?

Both StringBuilder and StringBuffer have a default initial capacity of 16 characters. When the content exceeds this limit, the capacity is automatically increased (usually doubled + 2). You can also set a custom capacity using the constructor.

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