StringBuffer vs. StringBuilder in Java: Key Differences Explained

In Java, Strings are immutable, which can cause performance issues when frequent modifications are needed. To solve this, Java introduced StringBuffer and StringBuilder for mutable strings.

Both classes offer similar functionality but differ in synchronization and performance. StringBuffer is synchronized, making it thread-safe but slower, while StringBuilder is not synchronized, making it faster but not thread-safe. For example, in a multi-threaded application, StringBuffer would be a safer choice, while StringBuilder would be preferred for single-threaded scenarios. 

In this blog, you will explore the key differences between StringBuffer vs. StringBuilder, focusing on their performance, synchronization, and best use cases.

What is the Difference Between StringBuffer vs. StringBuilder in Java?

StringBuffer and StringBuilder are Java classes for mutable strings. The key difference is synchronization: StringBuffer is thread-safe but slower, while StringBuilder is faster but not thread-safe.

In a benchmark with 10 million append operations, StringBuffer took 7,448 ms, while StringBuilder completed the task in 6,179 ms, demonstrating its superior speed. A micro-benchmark also showed StringBuilder outperformed StringBuffer in throughput (91,076 ops/s vs. 86,169 ops/s). 

However, StringBuffer ensures data integrity in multithreaded environments, which StringBuilder does not. Understanding these trade-offs helps you choose the right class for your needs.

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Comparison Table of StringBuffer vs. StringBuilder:

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Now that you have a good understanding of the differences between StringBuffer vs. StringBuilder in Java, let’s explore them each in more detail.

What is StringBuffer in Java? A Complete Guide

StringBuffer in Java is a mutable sequence of characters. Unlike String, which is immutable, StringBuffer allows modifications to the string content without creating new objects every time a change is made. 

This makes StringBuffer an ideal choice when working with strings that require frequent updates, such as in loops or dynamic string manipulations. One of its key features is that it is synchronized, making it thread-safe.

Features of StringBuffer:

• Mutable: Unlike String, StringBuffer allows you to modify the string content.
• Thread-Safe: StringBuffer is synchronized, making it safe for use in multithreaded environments.
• Efficient for Multiple Modifications: Since StringBuffer does not create new objects with every modification, it is more efficient for repeated string operations.
• Growable: The capacity of StringBuffer grows automatically as the string gets longer, preventing the need to manually resize it.

Example Code for StringBuffer in Java:

public class StringBufferExample {
    public static void main(String[] args) {
        // Creating a StringBuffer object
        StringBuffer sb = new StringBuffer("Hello");
        
        // Appending to the StringBuffer
        sb.append(" World!");
        
        // Inserting at a specific position
        sb.insert(6, "Java ");
        
        // Reversing the StringBuffer
        sb.reverse();
        
        // Output the result
        System.out.println("Modified StringBuffer: " + sb);
    }
}

• The StringBuffer object sb is initialized with the string "Hello".
• The append() method adds the string " World!" to the end of sb.
• The insert() method adds "Java " at the 6th position in the string.
• The reverse() method reverses the entire string content of sb.

Output:

Modified StringBuffer: !dlroW avaJ olleH

In this example, we see how StringBuffer efficiently handles string modifications by appending, inserting, and reversing, all while keeping the original object and without creating multiple instances like String would.

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Now that you understand what is StringBuffer, let’s explore StringBuilder in Java.

What is StringBuilder in Java? A Simple Explanation

StringBuilder in Java is similar to StringBuffer in that it allows for mutable sequences of characters. Unlike String, which is immutable, StringBuilder lets you modify strings without creating new objects each time. 

However, StringBuilder is not synchronized, making it faster than StringBuffer in single-threaded environments. It is ideal for applications where thread safety is not a concern and performance is a priority.

Features of StringBuilder:

• Mutable: Allows modifications to the string content without creating new objects.
• Faster than StringBuffer: Since it is not synchronized, StringBuilder performs better in single-threaded scenarios.
• Non-Thread-Safe: It is not thread-safe, making it unsuitable for use in multithreaded environments unless external synchronization is applied.
• Dynamic Capacity: Just like StringBuffer, StringBuilder dynamically grows in size as needed to accommodate the added content.

Example Code for StringBuilder in Java:

public class StringBuilderExample {
    public static void main(String[] args) {
        // Creating a StringBuilder object
        StringBuilder sb = new StringBuilder("Java");
        
        // Appending to the StringBuilder
        sb.append(" Programming");
        
        // Inserting at a specific position
        sb.insert(4, "Language ");
        
        // Reversing the StringBuilder
        sb.reverse();
        
        // Output the result
        System.out.println("Modified StringBuilder: " + sb);
    }
}

• A StringBuilder object sb is initialized with the string "Java".
• The append() method adds the string " Programming" to the end of sb.
• The insert() method inserts "Language " at the 4th position of the string.
• The reverse() method reverses the entire string content of sb.

Output:

Modified StringBuilder: gnimmargorP egauL avaJ

In this example, StringBuilder efficiently handles string manipulations like appending, inserting, and reversing. It's faster than StringBuffer because it does not use synchronization, making it ideal for single-threaded applications.

Also Read: Java Language History: Key Milestones and Development

Now that you know how StringBuilder differs from StringBuffer, let’s look at the similarities between the two.

Similarities Between StringBuffer and StringBuilder: What's Common Between Them?
While StringBuffer and StringBuilder have key differences, they share many similarities. Both classes are designed for mutable strings, meaning they allow modifications without creating new objects, which helps improve performance when working with strings that require frequent changes. 

They both offer similar methods for string manipulation, such as append(), insert(), reverse(), and delete(). Additionally, they provide a dynamic buffer that grows as the string content increases, ensuring efficient memory management. 

Here's a breakdown of their common features:

Common Features of StringBuffer and StringBuilder:

Both StringBuffer and StringBuilder are designed for performance when working with strings that undergo frequent modifications. While their thread-safety features differ, their core functionality for string manipulation remains quite similar.

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Next, let’s look at how they compare in terms of performance analysis.

Performance Analysis for StringBuffer vs. StringBuilder

StringBuilder outperforms StringBuffer in single-threaded scenarios because it lacks synchronization overhead. For example, in 1,000,000 operations, StringBuilder completes in 633 ms versus StringBuffer’s 808 ms. With 100,000,000 operations, StringBuilder finishes in 6,179 ms, while StringBuffer takes 7,448 ms. 

This performance gap is due to StringBuffer’s thread safety, which adds extra processing. In summary, use StringBuilder for speed in single-threaded code and reserve StringBuffer for thread-safe, multithreaded environments.

To check the performance of StringBuilder and StringBuffer, let us see an example with code:

public class Conc_Test{  
    public static void main(String[] args){  
  sTime = System.currentTimeMillis();  
        StringBuilder sb1 = new StringBuilder("Lorem");  
        for (int j=0; j<9999; j++){  
            sb1.append("Ipsum");  
        }  
        System.out.println("StringBuilder Time: " + (System.currentTimeMillis() - sTime)); 
        long sTime = System.currentTimeMillis();  
        StringBuffer sb2 = new StringBuffer("Lorem");  
        for (int j=0; j<9999; j++){  
            sb2.append("Ipsum");  
        }  
        System.out.println("StringBuffer Time: " + (System.currentTimeMillis() - sTime));  
           }  
}

As we can acknowledge from the code above, StringBuilder performs better than StringBuffer in speed. Additionally, the memory consumption of the two differs, with StringBuffer using more memory than StringBuilder.

Output:

StringBuilder Time: 0ms
StringBuffer Time: 15ms

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Next, let’s look at how upGrad can help you develop relevant skills for StringBuffer vs. StringBuilder in Java, so you can add it to your portfolio and enhance your career.

How Can upGrad Help You Learn StringBuffer vs. StringBuilder in Java?

Choosing between StringBuffer vs. StringBuilder depends on your application’s needs. Use StringBuffer in multithreaded environments, like a banking system, where thread-safety is crucial. For single-threaded applications, such as a game or real-time data processor, StringBuilder offers better performance due to its lack of synchronization. Understanding these scenarios ensures optimal performance and reliability in your Java projects.

To help you deepen your understanding of these classes and Java in general, upGrad offers specialized software development courses. These courses provide hands-on projects, the latest tools, and best practices in Java development, ensuring you’re well-prepared for the demands of 2025 and beyond.

In addition to the core Java topics, here are some free programs that can complement your learning journey:

• Data Structures & Algorithms
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• Programming with Python: Introduction for Beginners

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References:
https://blog.vanillajava.blog/2024/11/stringbuffer-is-dead-long-live.html
https://www.digitalocean.com/community/tutorials/string-vs-stringbuffer-vs-stringbuilder
https://www.baeldung.com/java-string-builder-string-buffer