Java Working with Numbers (Java: An Eventful Approach, Ch 3),

1. CS 120 Lecture 13 JavaWorking with Numbers(Java: An Eventful Approach, Ch 3), 23 October 2012 Slides Credit: Bruce, Danyluk and Murtagh

2. Recall: Accessing Location Info private Location firstPoint; public void onMousePress( Location pressPt ) { new Text("Pressed", pressPt, canvas ); firstPoint = press; } public void onMouseRelease ( Location releasePt) { new Text("Released", releasePt, canvas ); new Line( firstPoint, releasePt, canvas ); }

3. Being Unpredictable • Formal parameters: • allow us to refer to information that is unknown when the program is written • Generalize our methods • Are there other ways we access and use “unknown” information?

4. The Highs and Lows • What if we want to move an object only vertically by dragging the mouse? Pong: public void onMouseDrag( Location mousePos ) { paddle.moveTo( 10, mousePos.getY() ); }

5. Accessor Methods • Methods that return information about an object • Examples: mousePos.getY(); canvas.getWidth();

6. Expressions vs Statements • Statements: • “Top of the morning to you.” • paddle.moveTo(10,mousePos.getY() ); Perform a useful action • Expressions: • “the morning” • mousePos.getY() Used in statements

7. Fun with Numbers • initialPosition.getX() and -5 are both numbers • Can add, subtract, divide, multiply numbers • initialPosition.getX() + 5 • 5 - initialPosition.getX() • initialPosition.getX() / 5 • initialPosition.getY() * 3 • What happens with 9/5?

8. Order of Arithmetic Operations 2 + (initialPosition.getX() – initialPosition.getY()) * 5 • Precedence Rules: • Perform operations within parentheses first • Divisions and multiplications before additions and subtractions • Operations of equal precedence performed left to right • PE(MD)(AS)

9. Instance Variables • We can give names to numeric values as we can name objects private int brightness; // shades of gray brightness = 50;

10. Using Variables • First declare: private int brightness; private Color purple; • Then initialize brightness = 50; purple = new Color( 255, 0, 255 ); • We can also reassign values to variables brightness = 34; Unless…

11. Using Constants private static final int BRIGHTNESS = 255; • The keyword final indicates we cannot reassign a new value to brightness • The Java convention for naming constants is all caps

12. Displaying Numeric Information • We can combine numbers and text for display Text countDisplay; int programNum = 3; countDisplay = new Text("This is program #" + programNum, …); With text information the + operation does string concatenation!

13. System.out.println • Two ways to display textual information • Text class • System.out.println(…); • System.out.println("Number " + 5 ); • prints Number 5 to the Java Console

14. Playing Dice with the Universe • How can we simulate a roll of dice? • Through random numbers!

15. Random Numbers RandomIntGenerator die; die = new RandomIntGenerator( 1, 6 ); //display a random integer between 1 and 6 System.out.println( die.nextValue() );

16. public class RollAnotherOne extends WindowController { private static final int NUM_SIDES = 6; private RandomIntGenerator die = new RandomIntGenerator ( 1, NUM_SIDES ); public void begin() { new Text("Click to make me roll the dice ", TEXT_X, PROMPT_Y, canvas ); } public void onMouseClick (Location point ){ roll1 = die.nextValue(); roll2 = die.nextValue(); System.out.println("You rolled a " + roll1 + "and a " + roll2 + " for a total of " + ( roll1 + roll2 ) ); } }

17. Review • Numbers • Expressions and statements • Variables and Constants • System.out.println(…) • Generating random numbers

18. Student To Do’s • Read Java: An Eventful Approach • Ch. 3 (Today) • Ch. 4-5 • Practice, practice…. practice! • Work through examples by coding them! • Would you compete in a sport without practicing? • Would you perform on stage without practicing?