Java: creating an object in 3 single steps (Declaration, Allocation/Initialization, Assignment)

Question

I am not sure about the definiton of Declaration and Initialization. And when is setting the Default Values Initialization.

1) For example the Declaration of the object rocky (class Dog):

Dog rocky;

This creates only an entry in the stack and there is no reference?

.

2) Creating an Instance of Dog:

new Dog();

Memory Allocation in the Heap, Default Values Initialization (variable legs to 0), create a Reference.

If I have no constructor: the compiler creates a default constructor. Is it empty? Constructor and Default Values Initialization have to be different kettle of fish and is one of the possible Instance Initializer (next Instance Initializer Block and Constructor).

.

3) Assignment: put the Reference-Value into the stack?

rocky = new Dog();

Am I right?

Thanks

Sample:

class Dog
{
    int legs;

    Dog()
        {
            System.out.println("constructor invoked");
        }
}

public class Foo
{
    public static void main(String[] args)
        {
            Dog rocky;

            new Dog();

            rocky = new Dog();
        }
}

Answer 1

The following allocates memory for a pointer to a Dog object:

Dog rocky;

The following allocates memory for a Dog object:

new Dog();

And the following allocates memory for a Dog pointer and a Dog object and sets the pointer's value to the memory location of the newly created Dog object:

Dog rocky = new Dog();

-

The compiler writes the default initialization into each Constructor you defined. If you don't define one, the compiler creates a default one. Example:

int legs = 4;

will be converted to

int legs;
public Dog() {
    legs = 4;
}

The default inizialisations are the first statements in your constructor.