CP122 CS I. Abstract Interfaces, Graphical User Interfaces, Inheritance

Transcription

1 CP122 CS I Abstract Interfaces, Graphical User Interfaces, Inheritance

2 AirPods now available for order Tech News!

3 Tech News! AirPods now available for order Google reportedly stopping work on its own self-driving car

4 Hacker's Tip of the Day What's the difference between a 32-bit CPU and a 64-bit CPU?

5 Hacker's Tip of the Day 32-bit or 64-bit refers to the size of several things: RAM address size RAM value size CPU register size Size stored or loaded in one CPU operation

6 Hacker's Tip of the Day 2^32 around 4 billion (4 GB of RAM) 2^64 around 18 quintillion (18 EB of RAM)

7 Interfaces Some classes are related to one another based on the methods they define. How can we capture this relationship and add its structure to our programs?

8 Video Game Design Suppose we're writing a role-playing fantasy video game Players run around completing quests, fighting monsters, and picking up items

9 Video Game Design There are dozens of different kinds of items: Weapons, armor, potions, treasure, etc. Can we write classes for a couple of these items? Armor.java, Potion.java

10 Item Values Each item in our game had a value Each item in our game had a getvalue() method It would be great to capture the relationship between items that have values

11 Java Interfaces public interface HasValue { double getsellvalue(); double getbuycost();

12 Java Interfaces public interface HasValue { double getsellvalue(); double getbuycost(); This looks like a class, but it's an abstraction called an interface.

13 Java Interfaces public interface HasValue { double getsellvalue(); double getbuycost(); The interface has a name just like a regular class.

14 Java Interfaces public interface HasValue { double getsellvalue(); double getbuycost(); The body of the interface defines method headers (but no method bodies!)

15 Java Interfaces public interface HasValue { double getsellvalue(); double getbuycost(); This interface will be used by classes we create. These classes must define the interface's methods.

16 Java Interfaces public interface HasValue { double getsellvalue(); double getbuycost(); Notice that there isn't an access specifier out front...interface methods are automatically public.

17 Java Interfaces public class Potion implements HasValue {... public double getsellvalue() { return itemvalue; public double getbuycost() { return itemvalue * 2;

18 Java Interfaces public class Potion implements HasValue {... public double getsellvalue() { return itemvalue; public double getbuycost() { return itemvalue The class * that 2; implements the interface has to provide the actual body of the required methods.

19 Java Interfaces public class Potion implements HasValue {... public double getsellvalue() { return itemvalue; public double getbuycost() { return itemvalue It is an error * 2; to implement an interface and then fail to provide actual method implementations.

20 Instantiating an Interface? HasValue myitem = new HasValue();

21 Instantiating an Interface? HasValue myitem = new HasValue(); This is an ERROR because interfaces are abstract and cannot be instantiated.

22 Instantiating an Interface? Potion mypotion = new Potion(); We can only instantiate objects of classes that implement the interface.

23 Interface Variables? Potion mypotion = new Potion(); HasValue itemofvalue = mypotion; We can use variables of the interface type...they just have to contain an object from one of the implementing classes.

24 Interface Instance Variables? public interface HasValue { double getsellvalue(); double getbuycost(); Instance variables are not allowed within interfaces.

25 Interface Constants? public interface HasValue { int MAX_VALUE = ; double getsellvalue(); double getbuycost(); Interfaces CAN have constants. This values represents all the gold in the kingdom.

26 Armor.java and Potion.java

27 Inheritance Example: World of TextCraft Text

28 Creating Java GUIs Create a JFrame object Create and add components to the frame Buttons, textfields, labels, etc. Set the size of the frame Make the frame visible

29 MyFirstGui.java

30 MySecondGui.java

31 How do GUIs interact with the user? GUI are a form of event-driven programming Whenever the user does anything events are created: Move the mouse Click a button Type a key on the keyboard

32 How do GUIs interact with the user? To make our programs react to the user: GUI Component (e.g. Button) Event Listener

33 How do GUIs interact with the user? Event Listener Listen and react to user actions Has to implement a listener interface

34 An event listener that listens for clicks public class ClickListener implements ActionListener { public void actionperformed(actionevent event) { System.out.println("Click");

35 An event listener that listens for clicks public class ClickListener implements ActionListener { public void actionperformed(actionevent event) { System.out.println("Click"); We're implementing the ActionListener interface. What is required?

36 An event listener that listens for clicks public class ClickListener implements ActionListener { public void actionperformed(actionevent event) { System.out.println("Click"); This is the only required method: actionperformed.

37 MyThirdGui.java

38 Using an Inner Class That ClickListener isn't really used anywhere besides in our GUI class We may want to do things in our GUI based on clicks. How would we do that?

39 MyFourthGui.java