/*
  Author:  James Tam
  Version: January 27, 2021

  Learning objective: discovering that references are
  separate from the item (e.g. object, array) being referred
  to.
*/
public class Driver
{
    public static void main(String [] args)
    {
        //Reference to a person object not
        //an actual object.
        Person aPersonReference = null;

        //Reference to a string not a string.
        String stringReference = null;

        //Reference to an 'int' array no array has been created yet.
        int [] intArrayReference = null;

        //Runtime error 1: 'crashes' the program because no 
        //object exist yet (constructor hasn't been called).
        //The following will create a Person object if uncommented.
        //aPersonReference = new Person("Charlie Sheen");
        stringReference = aPersonReference.getName(); 

        //Runtime error 2: No string object exists yet.
        //Comment out the code for Runtime error 1 and you will
        //see the program crash when it attempts to call a 
        //String method on a non-existance object.
        //Either of the following will create String objects 
        //if they are uncommented.
        // stringReference = "abc";
        // stringReference = new String("Hru?");
        System.out.println(stringReference.toUpperCase());

        //Runtime error 3: No array exists yet.
        //Comment out the code for Runtime error 2 & 3 and you will
        //see the program crash when it attempts to access an 
        //element of an non-existance array.
        //The following will create an integer array if uncommented.
        //intArrayReference = new int[3];
        intArrayReference[2] = 888; 
    }
}