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StringBuffer and StringBuilder

Last Updated on December 6, 2023 by Ankit Kochar

In Java, both StringBuffer and StringBuilder are classes that provide mutable, or modifiable, sequences of characters. These classes are particularly useful when there is a need for frequent modifications to strings, as opposed to the immutable String class. The key difference between StringBuffer and StringBuilder lies in their synchronization behavior. StringBuffer is thread-safe, meaning it is synchronized and can be safely used in a multithreaded environment, whereas StringBuilder is not thread-safe, making it more efficient for single-threaded applications. Both classes offer methods to manipulate and modify strings dynamically, facilitating efficient string handling in Java programs.

What is StringBuffer in Java?

String Buffer in Java provides a straightforward and efficient way to manage strings and is generally used in many applications for string-related operations. String Buffer class in Java provides a number of methods for performing operations such as concatenating two strings, adding characters in a string, and removing characters from a string. The String Buffer class is similar to the String class in Java, but it differs in the aspect that String Buffer objects can be modified, whereas String objects are immutable (i.e., meaning that once created they cannot be changed later on).

To learn and explore more about StringBuffer in Java, please go to this page.

What is StringBuilder in Java?

The String Builder class in Java is very similar to the String Buffer class, with only a few differences. One of the differences is that the String Builder class is not thread-safe and because of this, its methods are found to be faster compared to the String Buffer methods. The String Builder class does not ensure synchronization, while the String Buffer class methods are synchronized. However, when most of the string operations are executed on the same thread, the String Builder class is preferred over the String Buffer class.

Syntax of StringBuilder Class in Java
The basic syntax for using the String Builder class in Java is

StringBuilder sb = new StringBuilder("PrepBytes");

Let’s take an example to understand how to use the String Builder class in Java

import java.util.*;
import java.lang.*;

class StringBuilderExample {

  public static void main(String[] args) {
    StringBuilder sb = new StringBuilder("PrepBytes");
    // Updating/Modifying the StringBuilder object value
    sb.append(" Articles");


PrepBytes Articles

Explanation: In the above example, we first create a String Builder object of “PrepBytes” and later on we try to append “articles” in our String Builder object to demonstrate its mutable string functionality.

StringBuilder Vs StringBuffer

There are some differences between String Buffer and String Builder class in Java and an overview of those differences is provided in the below StringBuilder Vs StringBuffer table.

Key Point StringBuffer StringBuilder
Basic StringBuffer was featured in the first release of Java. StringBuilder was first introduced in Java 5.
Performance It is thread-safe and because of this feature, many threads cannot access the same resource at the same time, thus operations in StringBuffer are slow. Since it is not thread-safe, string operations in StringBuilder are faster than String Buffer.
Synchronization It is synchronized. It is not synchronized.

In conclusion, StringBuffer and StringBuilder play crucial roles in Java programming, providing mutable string representations for scenarios that demand dynamic changes to string content. While StringBuffer ensures thread safety at the cost of some performance due to synchronization, StringBuilder sacrifices thread safety for enhanced efficiency in single-threaded applications. Developers must choose between these classes based on their specific application requirements, striking a balance between mutability and thread safety.

FAQ Related to StringBuffer and StringBuilder

Here are some frequently asked questions on String Buffer and String Builder classes in Java

Q1: Can I modify the contents of a StringBuffer or StringBuilder object after creation?
Yes, both StringBuffer and StringBuilder are mutable, allowing you to modify the sequence of characters they hold after creation using various methods.

Q2: Are StringBuffer and StringBuilder part of the Java Collections Framework?
No, StringBuffer and StringBuilder are not part of the Java Collections Framework. They belong to the java.lang package and are specifically designed for string manipulation.

Q3: Is there a significant performance difference between StringBuffer and StringBuilder for typical use cases?
In typical single-threaded scenarios, StringBuilder is more performant than StringBuffer due to its lack of synchronization overhead. However, the difference may not be noticeable for small-scale operations.

Q4: How does the length of a StringBuffer or StringBuilder affect memory usage?
The length() method of both classes returns the current length of the sequence. While increasing the length does not affect memory usage, decreasing it might result in unused memory, as the capacity remains unchanged.

Q5: Can I concatenate strings efficiently using StringBuffer or StringBuilder?
Yes, both classes provide append() methods, allowing you to concatenate strings efficiently. This is often more performant than using the + operator for concatenation, especially when dealing with multiple concatenations in a loop.

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