1. Reference Types CSCI-1302 Lakshmish Ramaswamy

2. Reference Variables Java supports 8 primitive types All other types are reference types Reference variable stores the memory address of where an object resides Null to indicate the variable is not referencing any object

3. Reference Example

4. Operations Type conversion Accessing internal field/method (dot operator) instanceof operator for verifying the type of a stored object Primitive operations are not allowed

5. Assignment Operator on References

6. Objects in Java Instance of a non-primitive type Reference variables store the memory location of the objects –Actual objects stored somewhere else –Object variables are a “name” for the memory location

7. dot Operator Accessing the internal field of an object Invoking methods on the object double Area = theCircle.area(); radius = theCircle.radius; Null Pointer exception if variable is storing a null reference

8. Declaration of Objects Button b; b.setLabel(“No”); p.add(b); Button b; b = new Button(); b.setLabel(“No”); p.add(b); Button b = new Button(“No”); p.add(b);

9. Garbage Collection Java destroys all objects that are not referenced Guarantees that object will be maintained if it is possible to access the object No guarantees on when an unreferenced object will be destroyed

10. “=“ Operator lhs = rhs means the value of rhs will be copied to lhs For objects memory location will be copied –lhs and rhs refer to the same object Button noButton = new Button (“no”); Button yesButton = noButton; yesButton.setLabel(“No”); p.add(noButton); p.add(yesButton);

11. Parameter Passing Value passed for objects is the reference So any method called is reflected upon the original copy public static void clearButton (Button b) { b.setLabel(“No”); B = null; }

12. Illustration of Parameter Passing

13. Project 1 Information CSCI-1302

14. Project Expectations Not using OO principles in the first assignment Will be done in a “procedural” fashion. Global variables should to be static and placed outside of main(). All methods should be static methods! Otherwise, must instantiate an object!

15. File/Class Name Your program should be named MineSweeper.java This means you have to create a class also called MineSweeper in this file. –public class MineSweeper

16. Static Final Variables (p. 20) Static Final variables are constants. –Ex. static final double PI = 3.14; Should be declared in all CAPS Declared outside of any function, but within the class declaration. These should be used whenever possible –I.e. NUM_ROWS, NUM_COLS for matrix dimensions.

17. The Board The board should be a 10x10 matrix of integers. –Int[][] board = new int[NUM_ROWS][NUM_COLS] Should store, COVERED, FLAGGED, or the integer representing # of adjacent mines.