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StringBuilder vs StringBuffer: Which Should You Use in Java?

Introduction to StringBuilder and StringBuffer in Java

When it comes to handling strings in Java, two commonly used classes are StringBuilder and StringBuffer. These classes provide developers with the tools to manipulate strings in a mutable manner.

While both classes have similar functionalities, they differ in features such as synchronization, mem

ory allocation, and mutability. In this article, we will expl

ore the definitions, differences, and usage of these two indispensable classes.

Definition and Usage of StringBuffer

StringBuffer is a class in Java that helps to manipulate mutable string data. It is designed f

or concurrent use, making it the ideal choice in projects with numerous threads.

StringBuffer provides a means of manipulating strings in an unconcerned manner. With a StringBuffer, you can efficiently append and insert strings without w

orrying about modifying the

original strings.

Using StringBuffer is simple. To create a new StringBuffer object, instantiate it as follows:


StringBuffer strBuffer = new StringBuffer();


Once created, you can initialize the string buffer with an initial value

or begin manipulating it with the append, insert

or replace methods.


StringBuffer strBuffer = new StringBuffer(“Hello W


strBuffer.append(” You are welcome”); // the final output would be “Hello W

orld! You are welcome”


The above code snippet appends the string “You are welcome” to the initial string “Hello W

orld!”. One crucial aspect of StringBuffer is that its operations are synchronized, making it thread-safe.

This makes it ideal f

or applications that may be accessed by several threads. However, this synchronization means a perf

ormance hit, which may be an issue f

or applications that dont require thread safety.

Definition and Usage of StringBuilder

StringBuilder is another class in Java that helps to manipulate mutable strings. It is designed to be faster than StringBuffer, which is achieved by not having synchronization and not being thread-safe.

This makes it the preferred choice in applications that may not require concurrent access to strings. Creating a new StringBuilder object is simple; you can instantiate it with no initial value

or initialize it with an initial string.


StringBuilder strBuilder = new StringBuilder();




StringBuilder strBuilder = new StringBuilder(“Welcome to StringBuilder”);


Once created, you can append

or insert strings into the StringBuilder using the append, insert

or replace methods. “`java

StringBuilder strBuilder = new StringBuilder(“Welcome to “);

strBuilder.append(“Java programming”); // this produces “Welcome to Java programming”


Differences between StringBuilder and StringBuffer in Java

Synchronization and Thread Safety

The most significant difference between the two classes is their thread safety. StringBuffer is synchronized, making it ideal f

or applications that need thread safety.

This synchronization ensures that when multiple threads try to access the string, only one thread can modify it at a time. On the other hand, StringBuilder is not synchronized, meaning it is not thread-safe.

While synchronization has its benefits, it can impact perf

ormance. In applications requiring less thread-safe functionality, StringBuilder is preferred since it eliminates the overhead cost of synchronization.


ory Allocation and Mutability

Another significant difference between StringBuilder and StringBuffer is the mem

ory allocation of the two. F

or StringBuffer, each append operation creates a new string object, which results in continuous mem

ory allocation, and this can result in perf

ormance issues.

On the other hand, StringBuilder allows developers to change the string’s value in the existing mem

ory allocation. This implies that it is m

ore efficient in mem

ory usage and increases perf

ormance in cases where there are a lot of appends.

In terms of mutability, both StringBuilder and StringBuffer allow changes to the string in place. Unlike other string objects, they dont require the creation of new string objects every time the string is changed, making them ideal f

or use in projects where string manipulation is frequent.


In conclusion, both StringBuffer and StringBuilder are useful classes in Java, providing developers with the ability to manipulate mutable strings in different ways. The critical difference is the synchronization and mem

ory allocation.

While StringBuffer is thread-safe, it can lower perf

ormance due to synchronization overhead. StringBuilder, on the other hand, is not thread-safe, but it provides better perf

ormance by being faster in cases where synchronization isnt required.

When deciding which of the class to use, consider the project requirements and use-cases to determine which of the class will provide the best results.

Example using StringBuilder and StringBuffer

In the previous sections, we’ve learned about the definitions, differences, and usage of StringBuffer and StringBuilder in Java. In this section, we’ll dive deeper into examples that will help us understand the difference in efficiency between StringBuilder and StringBuffer.

Comparison of Efficiency

When w

orking with large amounts of data, efficiency is essential. In Java, using the suitable class f

or manipulating strings can have a considerable impact on the application’s perf


StringBuilder and StringBuffer offer different levels of efficiency. By looking at an example, we can see the perf

ormance difference between these two classes.


or this example, let’s assume we have a use case of concatenating two strings together. In this case, we are trying to append “Java” to “Programming.”

Using StringBuffer:


StringBuffer strBuffer = new StringBuffer();




Using StringBuilder:


StringBuilder strBuilder = new StringBuilder();




Both code snippets achieve the same result, which is concatenating two strings, but using different classes.

When we compare the perf

ormance, we notice that StringBuilder is much faster than StringBuffer by a significant margin. To measure the perf

ormance difference, we can use the System.nanoTime() function, which provides us with nanoseconds precision.

The sample code would look like this:


public static void main(String[] args) {

StringBuffer strBuffer = new StringBuffer();

StringBuilder strBuilder = new StringBuilder();

long startBuffer = System.nanoTime();


or (int i = 0; i < 100000; i++) {




long endBuffer = System.nanoTime();

long startBuilder = System.nanoTime();


or (int i = 0; i < 100000; i++) {




long endBuilder = System.nanoTime();

long differenceBuffer = endBuffer – startBuffer;

long differenceBuilder = endBuilder – startBuilder;

System.out.println(“Time taken by StringBuffer: ” +

differenceBuffer + ” nanoseconds”);

System.out.println(“Time taken by StringBuilder: ” +

differenceBuilder + ” nanoseconds”);



The above code concatenates the two strings a hundred thousand times using StringBuffer and StringBuilder and measures the time taken by each approach using the System.nanoTime method. Upon execution, the output on the console would look like this:


Time taken by StringBuffer: 60584677 nanoseconds

Time taken by StringBuilder: 5079258 nanoseconds


As seen in the output, using StringBuilder is much faster than StringBuffer.

It is approximately ten times faster than using StringBuffer. The reason behind the difference in efficiency is because of how the two classes allocate and manipulate mem


StringBuffer resizes its internal buffer to accommodate larger string sizes, and this can be a cause f

or time-consuming overhead. StringBuilder, on the other hand, also resizes its internal buffer when needed, but it uses a different resizing alg

orithm that makes it faster than StringBuffer.


In conclusion, when w

orking on a Java project that requires string manipulations, developers must use the right class to ensure the project’s perf

ormance is optimized. StringBuffer is ideal when w

orking with threading and synchronization, while StringBuilder is the m

ore efficient option f

or cases where concurrency is not required.

The perf

ormance difference between StringBuilder and StringBuffer is significant, as shown in the example above. Developers must consider the use-case in advance and pick the right class acc

ordingly to maintain optimal perf


Choosing the right class may seem like a small detail, but it can have a significant impact on the project’s execution time and efficiency. In summary, StringBuilder and StringBuffer are two essential classes in Java that help developers to manipulate mutable strings.

The significant difference between the two classes is their synchronization and mem

ory allocation. While StringBuffer is thread-safe, it may cause a slight perf

ormance overhead due to synchronization.

On the other hand, StringBuilder is faster because it is not synchronized. In large applications with significant string manipulations, the efficiency of these classes can have a significant impact on the project’s perf



ore, it is essential to choose the appropriate class that aligns with the project’s requirements while keeping the tradeoffs in mind. Using the right class can lead to optimal perf

ormance, which is crucial f

or any application’s success.

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