String, StringBuffer, and StringBuilder in Java

Mutability Difference

The concept of immutability applies to the String class, whereas StringBuffer and StringBuilder are mutable classes that allow for modifications to their values.

When we say that String objects are immutable, it means that once a String object is created, its state (i.e., the sequence of characters it represents) cannot be modified. Any operation that appears to modify a String actually creates a new String object with the desired modifications, leaving the original String unchanged. This immutability property ensures that String objects are thread-safe and can be safely shared across different parts of a program.

On the other hand, StringBuffer and StringBuilder objects are mutable, meaning their values can be changed after creation. These classes provide methods for appending, deleting, or modifying the characters within the object, allowing for dynamic modifications. The difference between StringBuffer and StringBuilder lies in their synchronization behavior, with StringBuffer being synchronized and therefore suitable for multi-threaded environments, while StringBuilder is not synchronized and typically offers better performance in single-threaded scenarios.

The above code segment creates 500 new string variables. The "+" operator is overloaded for String and used to concatenated two string. Internally "+" operation is implemented using either StringBuffer or StringBuilder . In these type of situations you should use the Java StringBuffer/StringBuilder class.

When it comes to string operations that involve frequent modifications or concatenations, using mutable objects like StringBuffer or StringBuilder can indeed offer better performance compared to using String objects.

The reason behind this efficiency lies in the immutability of String objects. Since String objects cannot be modified directly, operations like concatenation require the creation of new String objects each time. This process involves allocating memory for the new object, copying the contents of the existing strings, and combining them. This can be computationally expensive and may lead to unnecessary memory allocation and deallocation.

On the other hand, StringBuffer and StringBuilder provide mutable alternatives specifically designed for efficient string modifications. These classes allow for in-place modifications, eliminating the need for repeated object creation. They offer methods like append() that efficiently append or modify the contents of the underlying string buffer without creating new objects.

In scenarios where string operations involve frequent modifications or concatenations, using StringBuffer or StringBuilder can help improve performance and reduce memory overhead compared to using String objects. These mutable classes provide a more efficient way to manipulate strings, making them ideal choices when dynamic modifications are required.

However, it's important to note that the choice between String and mutable classes should be made based on the specific requirements of the situation. If immutability and thread safety are paramount, String is the appropriate choice. If performance and efficient string modifications are the priority, StringBuffer or StringBuilder should be preferred.

Thread-Safety Difference

It is crucial to understand the contrasting characteristics of the StringBuffer and StringBuilder classes, particularly regarding their synchronization behavior and thread safety.

The StringBuffer class, as the name implies, is inherently synchronized, which renders it thread safe. This means that when multiple threads are involved, simultaneous invocation of StringBuffer methods by two threads is not permitted. The synchronization mechanism implemented within StringBuffer ensures that only one thread can access and modify the StringBuffer object at a given time. By enforcing this thread safety, StringBuffer guarantees the integrity and consistency of the data being manipulated.

Conversely, the StringBuilder class is designed to be non-synchronized, meaning it lacks built-in thread safety measures. Consequently, multiple threads can freely and concurrently call methods on the same StringBuilder object without encountering restrictions or synchronization barriers. The absence of synchronization in StringBuilder allows for parallel execution of operations, enhancing efficiency in multi-threaded environments. However, it is crucial to note that when working with StringBuilder in a multi-threaded context, proper synchronization mechanisms should be implemented externally to ensure data consistency and prevent race conditions.

Given the disparity in synchronization behavior, a key consideration arises: if multi-threading is not a requirement within your application, it is advisable to employ the StringBuilder class. The absence of internal synchronization in StringBuilder leads to enhanced performance, as there is no overhead associated with synchronization mechanisms. By utilizing StringBuilder, developers can utilize its efficiency to swiftly construct and manipulate strings in single-threaded scenarios.

Why we have two classes for same purpose?

The StringBuffer class is explicitly designed to be thread safe, ensuring that multiple threads can safely access and manipulate its contents. This inherent thread safety is achieved through the implementation of synchronization mechanisms within the StringBuffer class, which govern the concurrent access to its methods. The synchronization ensures that no two threads can simultaneously invoke methods on the same StringBuffer object, thereby preserving data integrity and preventing undesirable side effects that may arise from concurrent modifications.

On the other hand, the StringBuilder class, introduced in JDK 5 as an addition to the StringBuffer API, does not exhibit inherent thread safety. Unlike its synchronized counterpart, StringBuilder lacks built-in synchronization mechanisms, making it more suitable for scenarios where single-threaded environments are predominant. In such contexts, StringBuilder shines, offering superior performance and efficiency compared to StringBuffer. The absence of synchronization overhead allows StringBuilder to execute operations swiftly, catering to the demands of single-threaded applications.