Question

Shallow copy means a “copy” of an object with same values of their attributes whether primitive or reference values.

While performing shallow copy is it necessary to “create a new instance” ? as:

public class A {
    int aValue;
    B bObj;

    ...

    public A createShallow(A a1Obj) {
        A aObj = new A();
        aObj.aValue = a1Obj.aValue;
        aObj.bObj = a1Obj.bObj;

        return aObj;
    }
}

Or copy by assignment is also considered as shallow copy:

B b = new B(10);
A a = new A(1, b);

A a1 = a;

This article at wikipedia defines shallow copy as reference variables sharing same memory block. So according to this copy by assignment will also be a shallow copy.

But is not it a variables pointing to same object instead of “copy” of an Object ?

Answer 1

While performing shallow copy is it necessary to “create a new
instance” ?

Yes, you must create an instance to create a copy (either shallow or deep) of your object. Just doing the assignment of reference just creates a copy of reference which points to the same instance.

You have used a non-static method that is creating a copy. But generally I prefer two ways: –

Either use a copy-constructor: –

public A(A obj) {
    copy.aValue = obj.aValue;
}

And use it like: –

A first = new A();
A copy = new A(first);

Or, use a public static method which takes an instance and returns a copy of that.

public static A createCopy(A obj) {
    A copy = new A();
    copy.aValue = obj.aValue;
    return copy;
}