Cloning creates a copy of an object via Object.clone(). Cloneable is a marker interface with no methods — a class must implement it, or clone() throws CloneNotSupportedException. The default clone() is a shallow copy; classes needing a deep copy must override clone() to explicitly duplicate mutable referenced fields too.

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#Cloning#Cloneable

What is object cloning and the Cloneable interface in Java?

Why It's Widely Considered a Design Mistake

clone() is protected on Object (so you must override it just to make it callable), doesn't run any constructor (so invariants enforced by constructors are silently skipped), and Cloneable itself defines no clone() method — it just flips a hidden flag Object.clone() checks internally. Most modern Java code uses a copy constructor or static factory instead.

Cloneable: no methods, just a flag · Object.clone(): shallow by default, override for deep copy

Overriding clone() for a Deep Copy

java

class Box implements Cloneable {
    int[] items;

    @Override
    public Box clone() throws CloneNotSupportedException {
        Box copy = (Box) super.clone();
        copy.items = items.clone();   // deep-copy the array field too
        return copy;
    }
}