Difference between new operator in C++ and new operator in java

Question

As far as I know, the new operator does the following things: (please correct me if I am wrong.)

1. Allocates memory, and then returns the reference

Answer 1

In your "statement", I don't think "returns a reference to the first block of allocated memory is quite right. new returns a pointer (to the type of the object allocated). This is subtly different from a reference, although conceptually similar.

Answers to your questions:

1. In C++ an object stays around in memory (see note) until it is explicitly deleted with delete or delete [] (and you must use the one matching what you allocated with, so a new int[1];, although it is the same amount of memory as new int; can not be deleted with delete (and vice versa, delete [] can't be used for a new int). In Java, the memory gets freed by the garbage collector at some point in the future once there is "no reference to the memory".
2. Both throw an exception (C++ throws std::bad_alloc, Java something like OutOfMemoryError), but in C++ you can use new(std::nothrow) ..., in which case new returns NULL if there isn't enough memory available to satisfy the call.

Note: It is, as per comment, technically possible to "destroy" the object without freeing it's memory. This is a rather unusual case, and not something you should do unless you are REALLY experienced with C++ and you have a VERY good reason to do so. The typical use-case for this is inside the delete operator corresponding to a placement new (where new is called with an already existing memory address to just perform the construction of the object(s)). Again, placement new is pretty much special use of new, and not something you can expect to see much of in normal C++ code.