New A and new ();

Explain the meaning of the following statement:
1. new;

2. new ();

For the difference between new A and new A (), we can draw the following conclusion:
1. When the class body contains A display suitable for the default constructor, new A and new A () act the same way. They both call operator new to allocate memory and then call the default constructor to initialize the object.
2. When the class body has no display constructor, new A () first calls operator new to allocate memory for the object, and then uses null values to initialize the object member variable, while new A only calls operator new to allocate memory, and the object's member variables are meaningless random values! (Note: Applicable to basic data types, such as int)