Describing Similar Things In English, we commonly describe things by - PowerPoint PPT Presentation

Describing Similar Things In English, we commonly describe things by saying “it is like x except... ” For example: Mt. Holyoke is like other colleges except it only admits women. Java is like Flash except you create graphics by programming. 1 Types of Variation Extra behaviors: A strobe light is a light that flashes. Behavior has a different effect: A poisonous snake is a snake that delivers venom when it bites. Extra properties: A textbook is a book that includes exercises. 2 Is-A Hierarchies Animal Vertebrate Invertebrate Mammals Birds Fish Insects Worms 3 Tuesday, February 5, 13

Java Class Hierarchies Person UML Notation meaning is-a Student K12Student CollegeStudent 4 Java Class Hierachy public class Person { Superclass private String name; public Person (String theName) {…} public String getName() {…} } Subclass public class Student extends Person { public Student (String theName) {…} } 5 Inheritance Student “inherits” the public class Person { getName method. private String name; public Person (String theName) {…} public String getName() {…} } public class Student extends Person { public Student (String theName) {…} } Student s = new Student(“Alice”); System.out.println (s.getName()); 6 Tuesday, February 5, 13

Adding Behavior to a Subclass public class Student extends Person { private double gpa; public Student (string theName) {…} public void setGPA (double newGPA){…} } Student s = new Student(“Alice”); System.out.println(s.getName()); s.setGPA (3.6); Person p = new Person(“Bob”); System.out.println(p.getName()); p.setGPA (3.6); 7 Overriding Methods public class Person { public Person (String theName) {…} public String toString() { return name; } public String getName() {…} private String name; } A subclass can provide its own public class Student extends Person { definition of an private double gpa; public Student (String theName) {…} inherited method. public void setGPA (double newGPA){…} public String toString() { return getName() + “ has gpa “ + gpa; } } 8 public class Person { Overridden public Person (String theName) {…} public String toString() { Methods return name; } public String getName() {…} private String name; } public class Student extends Person { private double gpa; public Student (String theName) {…} public void setGPA (double newGPA){…} public String toString() { return getName() + “ has gpa “ + gpa; } } Person p = new Person(“Lucy”); System.out.println (p.toString()); 9 Tuesday, February 5, 13

public class Person { Overridden public Person (String theName) {…} public String toString() { return name; Methods } public String getName() {…} private String name; } public class Student extends Person { private double gpa; public Student (String theName) {…} public void setGPA (double newGPA){…} public String toString() { return getName() + “ has gpa “ + gpa; } } Student s = new Student(“Linus”); s.setGPA(3.1); System.out.println (s.toString()); 10 What is a Student? It is like a Person except that: It has a GPA The GPA can be set Since it is like a Person, it must have a name How does the name get set? 11 Constructing a Student public Student (String theName) { super (theName); gpa = 0.0; } The Student constructor calls the Person constructor. This must be the first statement in the subclass’ s constructor. 12 Tuesday, February 5, 13

extends JComponent public class HelloFromVenus extends JComponent { public void paintComponent (Graphics g) { super.paintComponent(g); int width = getWidth(); … } public static void main (String[] args) { … contentPane.add(new HelloFromVenus(), BorderLayout.CENTER); } 13 What is a JComponent? Something we can paint by overriding: public void paintComponent (Graphics g) Something that has a width, which we can find out by calling: public int getWidth () Something we can add to a panel, the content pane, … public Component add(Component comp) 14 JComponent Component Hierarchy Container means “extends” can also be read from bottom to top as “is a”. A JComponent JComponent “is a” Container. HelloFromVenus 15 Tuesday, February 5, 13

extends JPanel public class PizzaOrder extends JPanel { public PizzaOrder () { add (new JLabel (“Name”)); … } public static void main (String[] args) { … contentPane.add(new PizzaOrder(), BorderLayout.CENTER); } 16 What is a JPanel? Something we can add Swing components to: public Component add(Component comp) Something we can add to a panel, the content pane, … public Component add(Component comp) 17 Component Container JPanel Hierarchy JComponent JPanel PizzaOrder 18 Tuesday, February 5, 13

Animation Animation Works the same way as a movie - scene changes every 30 milliseconds To program an animation: Say that your class “extends Animation” Define the nextFrame method to update the scene. This is called every 30 milliseconds: protected void nextFrame() Call the start method to start the animation public void start() 19 Tuesday, February 5, 13