What approaches exist for creating immutable objects in object-oriented programming?

The following approaches are used to create immutable objects in object-oriented programming:

1. Using final classes and final fields (in Java) — the class is declared as final so it cannot be inherited, and fields are declared as final so they cannot be changed after initialization.

2. Absence of setters — do not provide methods to modify the object's state after creation.

3. Initializing all fields through the constructor — all values are set when the object is created.

4. Deep copying mutable objects — if an object contains references to mutable objects, their copies should be created so external changes do not affect the state.

Example of a simple immutable class in Java:

public final class ImmutablePoint {
    private final int x;
    private final int y;

    public ImmutablePoint(int x, int y) {
        this.x = x;
        this.y = y;
    }

    public int getX() { return x; }
    public int getY() { return y; }
}

Such an object cannot be changed after creation.