Difference between obj1 = obj.clone() and obj1= obj

[Minni Sharma]

Hi All,
Can you please tell me the difference between obj1 = obj.clone() {shallow cloning } and obj1= obj

[akhter wahab]

as i know obj1=obj.clone() in this a new obj1 will be made in the memory same as the obj
and by doing obj1=obj a new reference of obj is made named as obj1 in the memory new obj will not be made it will point the old obj ..

please consider my answer after confirming from at least one person more

[Rajesh Nagaraju]

obj1=obj.clone() -- does a shallow cloning

[Rob Spoor]

In most cases obj.clone() indeed returns a clone, or copy. This may be a shallow clone (by default), or a deep clone (if clone() has been overridden to clone all internals as well).

I said "in most cases" because technically it's allowed that obj1.clone() == obj1. This hardly ever occurs though; I still have to see the first occurrence in real code.

[Naman Patidar]

@Rob : obj1.clone()==obj1 will always return false. colne() method creates a bit-by-bit copy of object so the objects will have different hashcodes.
@ minni :
obj1 = obj.clone() {shallow cloning } : this will create a copy of obj object (a new object altogether) and assign it to obj1.
obj1= obj : this will assign same obj object to obj1;

[Vinoth Kumar Kannan]

if object.clone() does a bit by bit copy, then mustn't the hashcode values of both be same?! Just asking, I'm not sure though.

[Naman Patidar]

bit-by-bit copy means copy of object itself not of reference.

Object obj = new Object();
obj => is reference, pointing to actual object created by "new Object()".
reference contains a hashcode/value which in turn point to real object.

[Rob Spoor]

Naman Patidar wrote:@Rob : obj1.clone()==obj1 will always return false. colne() method creates a bit-by-bit copy of object so the objects will have different hashcodes.

Not necessarily. The API clearly states:

Creates and returns a copy of this object. The precise meaning of "copy" may depend on the class of the object. The general intent is that, for any object x, the expression:

x.clone() != x

will be true, and that the expression:

x.clone().getClass() == x.getClass()

will be true, but these are not absolute requirements. While it is typically the case that:

x.clone().equals(x)

will be true, this is not an absolute requirement.

The following are therefore all valid implementations:

public Object clone()
{
    return this; // so obj1.clone() == obj1
}

public Object clone()
{
    return "Hello World"; // so obj1.clone().getClass() != obj1.getClass() and !obj1.clone().equals(obj1)
}

However, it is very usual to use super.clone(), and if all classes up the chain do that then yes, obj1.clone() != obj1 and all fields are copied.