Say that the program has just been loaded and is just about to start running.
How many reference variables are there? 3
How many objects are there? Zero
Point
Objects
Here is a picture of the variables just as the program starts running.
No objects have been instantiated yet, so the reference variables
a
, b
, and c
do not refer to any objects.
To emphasize this, a slash has been put through the box for each variable.
import java.awt.*; class PointEg1 { public static void main ( String arg[] ) { Point a, b, c; // reference variables a = new Point(); // create a Point at (0, 0); // save the reference in "a" b = new Point( 12, 45 ); // create a Point at (12, 45); // save the reference in "b" c = new Point( b ); // create a Point containing data equivalent // to the data referenced by "b" } }
The program:
a
, b
, and c
,
which can hold references to objects of type Point
.Point
object with x=0 and y=0.a
.Point
object with x=12 and y=45.b
.Point
object that is similar to the second.c
.
Once each Point
object is instantiated, it is the same as any other
(except for the particular values in the data).
It does not matter which constructor was used to instantiate it.
What are the values of x
and y
in the third point?