4. The null Value



Answer:
  • What is the data type of the variable a?
    • a is a reference to a String object.
  • What is the data type of the variable b?
    • b is a reference to a Point object.
  • How many objects are there (so far)?
    • So far, there are no objects, just variables that can reference objects, once there are some.







The null Value



    

    

        
A reference variable holds information about the location of an object. It does not hold the object itself. This code

    

    





    

        

        

            
String a;
Point  b;

        

        

    





    

    

        
declares two reference variables but does not construct any objects. The following constructs objects and puts references in the variables:

    

    





    

        

        

            
a = "Elaine the fair" ;
b = new Point( 23, 491 );

        

        

    





    

    

    

        
null is a special value that means "no object." Set a reference variable to null when it is not referring to any object. Variables are often set to null when they are declared:

    

    





    

        

        

            
String a = null;
Point  b = null;



    
Question 3:
(Thought Question:) Do you think that null can be assigned to reference variables of any type? 
Click here for a .