Real World. static methods and Console & JavaFX App Intros. Lecture 16. Go ahead and PULL Lecture Materials & Sign-in on PollEv

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1 Go ahead and PULL Lecture Materials & Sign-in on PollEv Poll Everywhere: pollev.com/comp110 Lecture 16 static methods and Console & JavaFX App Intros Real World Spring 2016

2 Today Our first apps without magical COMP110 support code! But first static methods.

3 Methods We ve been learning about methods all semester How do we call a method? On an instance of a class. Example: My8Ball my8ball = new My8Ball(); my8ball.desperatelyshake(); System.out.println(my8Ball.getAnswer()); These are called instance methods.

4 Instance Methods An instance must be constructed before an instance method can be called on it. Instance variables hold values for as long as an instance is around in our program. We can read and change their values from instance methods. Continuing from Lecture 15 s example: we can model as many 8Balls in our program as we d like. After shaking any 8Ball, it maintains its state, meaning it continues to return the same answer until shaken again.

5 static Methods Sometimes methods are useful without the modeling power and flexibility instance-level variables give us round ing a double is an example method. Ideally, round is just a method we give a double argument and it returns it to us as a properly rounded double. Java allows us to write a method that can be called without an instance. Java calls it a static method.

6 static Methods By adding the static keyword to an instance declaration it is changed to a static method: public class Math { public static double round(double input) { // elided } } Static methods are called on classes: Math.round(4.20); For this reason, they re often called class methods. This is more descriptive than static methods until you take COMP520.

7 Useful Static Methods The java.lang.math class (available without importing!) defines a number of useful class methods: double Math.round(double n) double Math.cos(double rad) double Math.pow(double a, double n) // a n Math class docs: You ll come across others, for sure.

8 When to write your own static methods We won t practice writing static methods in COMP110* Why? They re less useful than instance methods and generally discouraged Knowing when to write static methods is a nuanced design decision You re free and encouraged to call static methods in the standard library, though, i.e. Math s methods * With one glaring exception the main method

9 The main Method In Java, and many other languages, the main method is where every program starts running You ve seen it in our runners! We ve just quickly launched from main into COMP110 support code: public class Runner extends ClassGalleryApp { public static void main(string[] args) { // Elided } } The main method is a void method. It must also be declared public and static. The main method has a single parameter with a funny looking type: String[] This is an low-level array of Strings. It s conceptually the same as ArrayList<String>. We ll talk about low-level arrays later

10 Hands-on: Hello World Redux 1. Right click in the Package Explorer. 2. Select New Java Project. 1. Name it HelloWorldRedux, click OK. 3. Right click the project. Select New Package 1. Name it comp110, click OK. 4. Right click the comp110 package. Select New Class 1. Name it ConsoleApp 2. Check the box: Which method stubs would you like to create : public static void main(string[] args) 5. In the main method, write: System.out.println( hello, world ); 6. Run it!

11 package comp110; public class ConsoleApp { public static void main(string[] args) { System.out.println("hello, world"); } }

12 The main Method Let s Party Like It s 1999 Console apps are all previous offerings of COMP110 ever programmed. Problem sets, too.

13 Writing Graphical User Interfaces with JavaFX For the back side of this semester we ll be writing real GUI applications All of the Support Code GUIs you ve used so far were written with JavaFX JavaFX a BIG library that allows you to write apps using 2D graphics, 3D graphics, forms, controls, animations, sound, images, etc We only have time to explore a small portion of it, however, you ll get a real sense of what it s like

14 Code walk-through of comp110.lecture16.javafxapp

15 Adding a Button First: import javafx.scene.control.button; Do this after the label, before stage.show(); Declare a local variable Type: Button Name: shakebutton Initialize using Button(String label) constructor where label is Shake the 8 Ball! Add it to _pane s children: _pane.getchildren().add(shakebutton);

16 Button shakebutton = new Button("Shake the 8 Ball"); _pane.getchildren().add(shakebutton);

17 How do we make the button do something when pressed? We must tell the button what we want it to do when an action (like click) happens This is called event handling. When some event happens, how do we want the program to handle it? Events in programs include: mouse clicks, finger taps, key presses, and so on

18 Button s setonaction Method Button has a method named setonaction. It s signature looks like: void setonaction(eventhandler<actionevent> handler) Uh, what?!? Event handling can be complicated, luckily Java gives us an easy way to make EventHandlers We can provide a reference to an instance method that will be called when an action is taken shakebutton.setonaction(this::shakepressed); This is a method reference. This line reads hey, shakebutton, when you are pressed call my shakepressed method.

19 Button shakebutton = new Button("Shake the 8 Ball ); shakebutton.setonaction(this::shakepressed); _pane.getchildren().add(shakebutton);

20 Adding the Reveal Button Declare another local variable Type: Button Name: revealbutton Initialize using Button(String label) constructor where label is Reveal the Answer! Wire it up to call the revealpressed method when the button is clicked. Add it to _pane s children: _pane.getchildren().add(revealbutton);

21 Button revealbutton = new Button("Reveal the Answer"); revealbutton.setonaction(this::revealpressed); _pane.getchildren().add(revealbutton);

22 Hands-on: Adding a My8Ball 1. Declare an instance variable Visibility: private Type: My8Ball Name: _8ball 2. In the start method, initialize it to a new instance of My8Ball 3. In the shakepressed method, call the desparatelyshake method on _8ball 4. In the revealanswer method, call the getanswer method on _8ball and assign it to the answer variable 5. Run your app! 6. Check-in on PollEv.com/comp110

23 /* Instance Variables */ private VBox _pane; // Vertical Box stacks its controls downward. private My8Ball _8ball; // // Within the start method: public void start(stage stage) { // _8ball = new My8Ball(); // } public void shakepressed(actionevent e) { _8ball.desperatelyShake(); } public void revealpressed(actionevent e) { String answer = _8ball.getAnswer(); Alert alert = new Alert(AlertType.INFORMATION, answer); alert.show(); }

24 Follow Along: Packaging 1. Right click the project 2. Select Export 3. Choose Runnable JAR 4. Under Launch Configuration select JavaFXApp - Lecture Choose your Desktop as the Destination 6. Double click the JAR file from your desktop