What does immutability of objects mean and what are its advantages and disadvantages?

Objects are immutable if, after creation, their state cannot be changed — all their fields remain constant.

Advantages:

• Thread safety: immutable objects can be used safely in multithreaded environments without synchronization.
• Simplicity: fixed state reduces errors.
• Caching and reuse: immutable objects can be safely stored and transferred.

Disadvantages:

• Performance: changing an object requires creating a new one, which can lead to additional memory and time costs.
• Flexibility: not always convenient, especially if the object needs to be changed frequently.

In Java, immutable objects are usually created using:

• final fields
• no setters
• initializing all fields via constructor

Example:

public final class Person {
    private final String name;
    private final int age;

    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public String getName() { return name; }
    public int getAge() { return age; }
}

Such an object cannot be changed after creation.