Why is immutability so important in programming?

Immutability provides several advantages:

• Safety in multithreaded environments: Immutable objects can be safely shared between threads without the need for synchronization or locks, simplifying the development of multithreaded applications and preventing data races.
• Predictability: The state of an immutable object never changes after creation. This simplifies understanding the data flow in a program and debugging, as you know exactly that the object will not change unexpectedly.
• Caching and memoization: Immutable objects are easy to cache. If two objects are equal (equals), their hash codes will always be the same (assuming correct implementation of hashCode), and their state will not change, allowing safe reuse of computed results.
• Design simplification: Designing with immutable objects can lead to more modular and understandable code. Functions that accept and return immutable objects are pure and have no side effects on input data.
• Performance improvements in some cases: Although creating a new object for each change might seem inefficient, the JVM garbage collector is optimized for handling a large number of short-lived objects, and the absence of locks in a multithreaded environment can offset the costs.

Example of creating an immutable class:

public final class ImmutableClass {

    private final int value;
    private final String name;

    public ImmutableClass(int value, String name) {
        this.value = value;
        this.name = name;
    }

    public int getValue() {
        return value;
    }

    public String getName() {
        return name;
    }

    // No setters
    // final fields
    // final class
    // All fields are primitives or other immutable objects,
    // or return copies of mutable objects when necessary (none here)

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        ImmutableClass that = (ImmutableClass) o;
        if (value != that.value) return false;
        return name != null ? name.equals(that.name) : that.name == null;
    }

    @Override
    public int hashCode() {
        int result = value;
        result = 31 * result + (name != null ? name.hashCode() : 0);
        return result;
    }
}