What is an Immutable Object?

An immutable object is an object that cannot be modified once it has been created. In other words, its state cannot be changed after it has been instantiated. Any attempt to change its value results in the creation of a new object with the updated value, leaving the original object unchanged.

This concept is often used in programming languages that support functional programming, where immutability is a key feature. Immutable objects are useful in situations where the state of an object should not be changed, such as in multi-threaded environments where concurrent access to mutable objects can lead to race conditions and data corruption.

Immutable objects have several advantages over mutable objects. Firstly, they are thread-safe and can be safely shared between threads without the need for synchronization. Secondly, they are easier to reason about, as their state cannot change unexpectedly. Thirdly, they can be used as keys in hash tables and sets, as their hash value is fixed and does not change over time.

Examples of immutable objects in Java include String, Integer, and LocalDate. Once a String object has been created, its value cannot be changed. Any attempt to modify it results in the creation of a new String object with the updated value. Similarly, once an Integer object has been created, its value cannot be changed.

Immutable objects are not suitable for all situations, however. In some cases, mutable objects are more appropriate, such as when the state of an object needs to be updated frequently. In these cases, it is important to ensure that access to mutable objects is synchronized to prevent race conditions and data corruption.

In summary, an immutable object is an object that cannot be modified once it has been created. It is useful in situations where the state of an object should not be changed, such as in multi-threaded environments. Immutable objects have several advantages over mutable objects, including thread-safety, ease of reasoning, and suitability for use as keys in hash tables and sets.