Object Cloning in Java: Create Exact Copies of Objects

Learn how to clone objects in Java using the clone() method from the Object class. Understand the importance of implementing the Cloneable interface in your class to enable cloning and how to handle CloneNotSupportedException when the interface is not implemented.

Object Cloning in Java

Object cloning is a way to create an exact copy of an object. The clone() method of the Object class is used for this purpose.

The java.lang.Cloneable interface must be implemented by the class whose object we want to clone. If not, the clone() method throws CloneNotSupportedException.

Syntax of the clone() method:


protected Object clone() throws CloneNotSupportedException

Why use `clone()` method?

The clone() method saves the extra processing needed to create an exact copy of an object using the new keyword.

Advantages of Object Cloning

Saves writing lengthy and repetitive code.
Easiest and most efficient way to copy objects, especially in old projects.
Fastest way to copy arrays.

Disadvantages of Object Cloning

Requires changes to syntax: implementing Cloneable, defining clone(), and handling CloneNotSupportedException.
The Cloneable interface has no methods, just indicates the ability to clone.
Object.clone() is protected, so we must provide our own clone() method.
Object.clone() doesn't invoke any constructor, so we have no control over object construction.
Supports only shallow copying; we must override for deep cloning.

Example of `clone()` method

Syntax


class Student18 implements Cloneable {
int rollno;
String name;

Student18(int rollno, String name) {
  this.rollno = rollno;
  this.name = name;
}

public Object clone() throws CloneNotSupportedException {
  return super.clone();
}

public static void main(String args[]) {
  try {
    Student18 s1 = new Student18(101, "amit");
    Student18 s2 = (Student18) s1.clone();

    System.out.println(s1.rollno + " " + s1.name);
    System.out.println(s2.rollno + " " + s2.name);

  } catch (CloneNotSupportedException c) {
    c.printStackTrace();
  }
}
}

Output


101 amit
101 amit

In the example above, both reference variables have the same values. The clone() method copies the values of an object to another object.

If we create another object using the new keyword and assign the values, it will require a lot of processing. To save this processing, we use the clone() method.

Object Cloning in Java: Create Exact Copies of Objects