Shallow Vs Deep cloning sample

 

Shallow Cloning vs Deep Cloning in Java

The easiest way to remember:

Shallow Copy → copies the object, but shares referenced objects.
Deep Copy → copies the object AND creates copies of referenced objects.

1. Simple Example

Suppose we have a Person containing an Address.

class Address {
    String city;

    Address(String city) {
        this.city = city;
    }
}

class Person implements Cloneable {
    String name;
    Address address;

    Person(String name, Address address) {
        this.name = name;
        this.address = address;
    }

    // Shallow copy
    @Override
    protected Person clone() throws CloneNotSupportedException {
        return (Person) super.clone();
    }
}

Shallow Copy

Address address = new Address("Bangalore");

Person p1 = new Person("Ramesh", address);

// Shallow clone
Person p2 = p1.clone();

p2.address.city = "Hyderabad";

System.out.println(p1.address.city);

Output:

Hyderabad

Why?

           p1
            |
            |---- name = Ramesh
            |
            ↓
        Address A
        city = Hyderabad
            ↑
            |
            |---- p2

Both p1 and p2 point to the same Address object.

So:

p1.address == p2.address

is:

true

---

2. Deep Copy

For deep cloning, we create a new Address object as well.

class Person implements Cloneable {
    String name;
    Address address;

    Person(String name, Address address) {
        this.name = name;
        this.address = address;
    }

    @Override
    protected Person clone() throws CloneNotSupportedException {
        Person copy = (Person) super.clone();

        // Create a new Address object
        copy.address = new Address(this.address.city);

        return copy;
    }
}

Now:

Address address = new Address("Bangalore");

Person p1 = new Person("Ramesh", address);
Person p2 = p1.clone();

p2.address.city = "Hyderabad";

System.out.println(p1.address.city);
System.out.println(p2.address.city);

Output:

Bangalore
Hyderabad

Because:

       p1                    p2
        |                     |
        ↓                     ↓
   Address A             Address B
   Bangalore             Hyderabad

They have different Address objects.

p1.address == p2.address

returns:

false

---

Interview Shortcut ⭐

Shallow Clone	Deep Clone
New outer object	New outer object
Referenced objects are shared	Referenced objects are also copied
Faster	More expensive
Changes to nested object affect both	Changes are independent
super.clone() typically gives shallow copy	Need to explicitly clone/copy nested objects

One-line interview answer

Shallow cloning creates a new object but copies references as-is, whereas deep cloning creates a new object and recursively creates independent copies of referenced mutable objects.

Easy memory trick

Shallow = New Box + Same Objects
Deep    = New Box + New Objects

Important: Object.clone() by itself performs a shallow copy. Deep cloning is something you must implement explicitly (or use another copying strategy).