Default constructor is automatically called after an object is created.
But in Java when we allocate memory using new operator i.e. classname obj = new classna
classname obj = new classna
If we consider an example like
classname obj = new classname();
classname obj initialize the object and new classname(); allocates memory location for the object. If you have a constructor, then the constructor is called, otherwise default constructor is called.
classname obj
new classname();