Difference between c++ and java Object creation

[rohan yadav]

Hi everyone, This question was asked in an interview of mine,

Why it is always necessary to use new operator while creating object in Java, while there is no such a need in c++??

Can anyone tell me the answer

[Manish Singh]

Do we always use new to create objects in Java?

What about

String s1 = "abc";

int i1 = 10;

int [] ar = {1,2,3}

[Alec Lee]

Also, I can create new object by these in Java:

    
   Object o = Class.forName("abc.MyClass").newInstance();

No new operatior involved.

[Alec Lee]

Maybe the interviewer want to test whether you know the difference between class concept in C++ and Java (but using a bad question). I don't know about C++ much. But as I recall, C++ class is just a compiler construct (someone please correct me if I am wrong). It doesn't exist in runtime. Java class is a real entity existing in runtime - as represented by the Class object for that class.

[David Newton]

Manish Singh wrote:int i1 = 10;

Not an object.

[Campbell Ritchie]

David Newton wrote:

Manish Singh wrote:int i1 = 10;

Not an object.

He must have meant Integer i1 = 10;

[Henry Wong]

I think this question is better answered from the C++ side, than the Java side -- as from the Java side, you'll just get into small details like the reflextion, autoboxing, etc. etc. etc..... not that it is wrong, but the answer is simpler from the C++ view.

In Java, all variables to objects are references. In C++, you can declare a variable to objects, just like any other type. You can declare a variable of that object type. You can declare a pointer to it. etc. The "new" operator is only needed when you want to allocate (and construct) the object, for assignment to a pointer. If it is not a pointer, then it is not necessary.

Henry