CLONING OBJECT IN JAVA

We can copy an object in 3 different ways. They are -

Shallow copy – It is a bit-wise copy of an object. A new object is created that has an exact copy of the values of the original object. If any of the fields of the object refers to other objects, just the reference addresses are copied i.e., only the memory address is copied.

Let us take an example –

class  A

{

int i;

int j;

}

A obj = new A();

obj.i=1;

obj.j=2;

A obj1 = obj;     //  Line 1

Here in the above comment section Line 1 we are not creating a new object, instead we are creating a  reference variable which is pointing to the object of obj in the heap. So in this situation, if we change the value of obj then obj1 will also get reflected. So inside our heap there will be one object, and inside stack we will have two reference pointing to same object in the heap.

Example –

public class Clon {

          int i;

          int j;

          @Override

          public String toString() {

                   return "i = "+i+" j = "+j;

          }

          public static void main(String[] args) {

                   Clon obj = new Clon();

                   obj.i=10;

                   obj.j=20;

                   Clon obj1 = obj;

                   System.out.println(obj);

                   System.out.println(obj1);

                   obj1.i=30;

                   System.out.println(obj);      // both gets reflected

                   System.out.println(obj1);

          }

}

Output –

i = 10 j = 20

i = 10 j = 20

i = 30 j = 20

i = 30 j = 20

Deep Copy – a deep copy copies all fields and makes copies of dynamically allocated memory pointed to, by the fields. A deep copy occurs when an object is copied along with the objects to which it refers. In deep copy we will create a new object and manually we will copy one-one value from one object to another.

Let us take an example –

class  A

{

int i;

int j;

}

A obj = new A();

obj.i=1;

obj.j=2;

A obj1 = new A();

obj1.i = obj.i;

obj1.j=obj.j;

In the above example even if any object value gets changed it doesnot reflect to the existing value of another object. Suppose if we have thousands of variables, then it’s not possible to go with deep copy.

Example –

public class Clon {

          int i;

          int j;

          @Override

          public String toString() {

                   return "i = "+i+" j = "+j;

          }

          public static void main(String[] args) {

                   Clon obj = new Clon();

                   obj.i=10;

                   obj.j=20;

                   Clon obj1 = new Clon();

                   obj1.i=obj.i;

                   obj1.j=obj.j;                  

                   System.out.println(obj);

                   System.out.println(obj1);

                   obj1.i=30;

                   System.out.println(obj); // i value not reflected

                   System.out.println(obj1);             

          }

}

Output –

i = 10 j = 20

i = 10 j = 20

i = 10 j = 20

i = 30 j = 20

Cloning – Cloning is the combination of deep copy and shallow copy. Here we don’t have to create object, clone will automatically create the object and it will copy all the values into the new object. To clone an object simply we are not allowed, we have to give some permissions using Cloneable interface which means the class should implements cloneable interface and overrides clone() method. Cloneable interface is a marker interface without any method declaration.

Example –

public class Clon implements Cloneable{

          int i;

          int j;

          @Override

          public String toString() {

                   return "i = "+i+" j = "+j;

          }

          public Object clone() throws CloneNotSupportedException{

                   return super.clone();

          }

          public static void main(String[] args) throws CloneNotSupportedException {

                   Clon obj = new Clon();

                   obj.i=10;

                   obj.j=20;

                   Clon obj1 = (Clon)obj.clone();

                   System.out.println(obj);

                   System.out.println(obj1);

                   obj1.i=30;

                   System.out.println(obj);

                   System.out.println(obj1);

          }

}

Output –

i = 10 j = 20

i = 10 j = 20

i = 10 j = 20

i = 30 j = 20