What does immutability mean in Java?

• A. Objects can be modified after creation
• B. Objects cannot be created without parameters
• C. Objects cannot be modified after they are created
• D. Objects can change states frequently

Answer: (C)

Immutability in Java refers to the property of an object that prevents its state from being modified once it has been created. When an object is immutable, its fields cannot be changed, which means that any operation that appears to modify the object actually results in the creation of a new object instead. This characteristic is useful for several reasons, including improved thread safety, ease of use, and consistent behavior.

For example, the String class in Java is immutable. When you create a new string or perform operations such as concatenation, the original string remains unchanged; instead, a new string object is created. This ensures that the original content is preserved and can safely be accessed by multiple threads without additional synchronization.

Understanding immutability is crucial in object-oriented programming as it promotes simpler and more predictable code. This is particularly important in concurrent programming, where immutable objects can be shared among threads without the risk of being altered unintentionally.