How to make object in java. I have Test Class but not constructor

Question

I'm very confused about object:

I'm creating a object Here is my Test Class : Test.java

public class Test {

     public static void main(String[] argc){
      Test obj; //1. ---> here object is created
      Test obj = new Test(); //2. --> or here object is created
      }
    }

Please

Answer 1

Every class without a self-coded constructor has the so called default contructor . This one is invisible and would have this code:

public Test() {

}

In line 1 you only declare a variable of type Test . In line 2 you actually create an object of type Test and assign it to the variable obj .

Answer 2

The first version

Test obj;

just declares obj value, not creates it. You can use it later in your code. Currently it contains null pointer, or points to nothing.

In the second version

Test obj = new Test();

combines declaration ( Test obj ), creation ( new Test() part) and assignment ( = ).

Answer 3

As explained in this java tutorial , Object creation as three parts:
1. Declaration : To declare obj variable:
Test obj;

It simply declares a variable. For primitive variables, this declaration also reserves the proper amount of memory, but for reference variables it does not create object.

2. Instantiation : To instantiate obj variable:
   Test obj = new Test();

Operator new is required to allocate memroy for the obj and returning the reference to that memory. The new operator also invokes the object constructor.

3. Initialization : To initialization obj variable it's constructor needs to be called. In Java, constructor is invoked by the new operator. In other languages eg C, C++ when you instantiate any variable using malloc it doesn't call constructor, which needs to be called explicitly. However new operator behaves similar.