JAVA Syllabus
QUESTIONS & ANSWERS

Difference between String and StringBuffer class?

In Java, both the String class and the StringBuffer class are used to work with text data, but they have significant differences in terms of their immutability, performance, and usage. Let's explore the differences between the String class and the StringBuffer class:

  1. Immutability:
  • String: As mentioned earlier, the String class in Java is immutable, meaning once a String object is created, its value cannot be changed. Any operation that appears to modify a String, such as concatenation or substring extraction, actually creates a new String object with the modified content. This immutability ensures that String objects are thread-safe, hashable, and can be safely shared among different parts of a program.

  • StringBuffer: In contrast, the StringBuffer class is mutable. It allows you to modify its content after creation. You can append, insert, or delete characters in a StringBuffer without creating new objects. This makes StringBuffer more efficient when it comes to frequently changing the contents of a string.

  1. Performance:
  • String: Due to its immutability, working with String objects can result in performance overhead when performing operations that create new String objects, especially in scenarios with frequent modifications or concatenations. Each time you perform an operation on a String, a new String object is created, leading to unnecessary memory allocation and garbage collection.

  • StringBuffer: Because StringBuffer objects are mutable, they are more efficient when it comes to frequent modifications. Appending or modifying the content of a StringBuffer does not require creating new objects, as the content can be modified directly in the underlying buffer. This makes StringBuffer more suitable for scenarios where you need to build or modify strings dynamically.

  1. Thread Safety:
  • String: As immutable objects, String instances are inherently thread-safe. Multiple threads can share and read the same String object without any concerns about concurrent modifications.

  • StringBuffer: The StringBuffer class includes built-in synchronization to make it thread-safe. This means multiple threads can safely modify a StringBuffer object without encountering data corruption. However, this synchronization comes with a performance cost, which makes StringBuffer less efficient for single-threaded scenarios.

Usage Recommendations:

  • Use String when you have a fixed text that doesn't require frequent modifications. For example, when dealing with constants or configuration values.
  • Use StringBuffer when you need to build or modify strings dynamically, especially in multi-threaded environments where thread-safety is required. It is commonly used for string manipulations in performance-critical or concurrent applications.


Java 5 onwards, there's also the StringBuilder class, which is similar to StringBuffer but lacks synchronization, making it more efficient in single-threaded scenarios. If you don't need thread-safety, StringBuilder is often preferred over StringBuffer due to its better performance.

25/07/2023, 11:49 am Read : 165 times