Strings and Object References in Java

The String class is used for text manipulation. As you read, you will learn different ways to create Strings, methods to manipulate Strings, the String concatenation operator '+', and about how Strings are immutable.

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 .