Advanced Java Programming CSE 7345/5345/ NTU 531

1. Welcome Back!!! Advanced Java ProgrammingCSE 7345/5345/ NTU 531 Session 7

2. Office Hours: by appt 3:30pm-4:30pm SIC 353 Chantale Laurent-Rice Welcome Back!!! trice75447@aol.com claurent@engr.smu.edu

3. Short reviewPackages • In Java, each class is defined in a single file called ClassName.java. • A package is a name for a set of related classes, • Java uses package names to locate classes at compile-time and at runtime. • Packages can be seen as some kind of libraries in which the classes are grouped. • The difference is that packages provide an additional scope. • Each class file must belong to a package: • Example: • Package dpack; • Package java.awt.event;

4. Packages con’t • If no package is given, the class is placed in a default package with no name. • A compilation unit (a file) declares one or more classes. It is a file that may contain several class declarations. It is used as an input for the java Compiler (javac) which outputs a series of class files (bytecodes). • There is a class file for each class in the compilation unit. • At the most one class is declared public. Example: Source code: ClassName.java hello.java Bytecode: className.class hello.class

5. Packages con’t • To use the classes, one or more modules in a program can import the entire package with the declaration, such as import graphics.*; • The asterisk indicates to the compiler that it should import all classes in the graphics package.

6. Standard packages • Java.applet- provides the means to create applet • Java.awt- provides class-based GUI with windows • Java.awt.*- have subpackages such as java.awt,color, java.awt.font, and java.awt.image • Java.beans- provides basic elements for JavaBeans • Java.io- provides I/O • Java.lang- wrapper classes such as: Char, int, Double, String and StringBuffer • java.math- math programmers • Java.net- network, socket handler, internet utility classes • Java.rmi- Remote Method Invocation provide support for distributed code controlled by remote interface • Java.security- implements security, encryption keys, and certificates • Java.sql- implements of Structured Query Language database fields types and methods • Java.text- provide parsers and formatters • Java.util- Java Application and applet (Random class, Collection, list, Set) packages container class. • Java.util.jar- subpackage w/I java.util. • Java.util.zip- subpackage for .zip file compression format.

7. Packages con’t • To import just one class: import graphics.Rectangle; • It is not correct to import the package itself: import graphics; • Some packages provide one or more subpackages, such as java.util.jar, a subpackage of java.util. • Importing a package does not import any subpackages. • You must do that explicitly using statements like these: • Import java.utils.*; • Import java.utils.jar.*;

8. What happen if you tried to compile and run the following code? public class EqualsTest{ public static void main(String[] args){ Long L = new Long( 7 ); 4. if( L.equals( 7L)) 5. System.out.println(“Equal”); else System.out.println(“Not Equal”); 6. } 7. } Small Quiz • The program would compile and print “Equal” • The program would compile and print “Not Equal”. • The compiler would object to line 4. • A runtime cast error would occur at line 4.

9. Small Quiz C. qualsTest.java:5: cannot resolve symbol symbol : method equals (long) location: class java.lang.Long if( L.equals( 7L)) ^ 1 error • The compiler knows that the equals method takes an Object rather than a primitive as input. Because the compiler does not compile answer a, b, d are incorrect.

10. What happen if you tried to compile and run the following code? public class EqualsTest{ public static void main(String[] args){ Object A = new Long ( 7 ); Long L = new Long( 7 ); 5. if( A.equals( L )) System.out.println(“Equal”); 6. else System.out.println(“Not Equal”); 7. } 8. } Small Quiz • The program would compile and print “Equal” • The program would compile and print “Not Equal”. • The compiler would object to line 5. • A runtime cast error would occur at line 5.

11. Small Quiz a. • Because the Long object created in line 3 does not lose its identity when cast to Object A, so the equals method knows the class is correct and compares the values. • Answer c, d, do not occur because this is the correct form for comparing objects with the equals method. Therefore, they are incorrect.

12. class D3 implements B { public void display() { System.out.println("D3"); } } class InterfaceRefVar{ public static void main(String[] args){ B b; b = new D1(); b.display(); b = new D2(); b.display(); b = new D3(); b.display(); } } interface B{ void display(); } class D1{ } class D2 implements B{ public void display() { System.out.println("D2"); } } interface What compile-time error is generated for the following program?

13. interface The line “b = new D1();” generates an error because the types are incompatible for assignment. Class D1 does not implements interface B. • C:\InterfaceRefVar.java:23: incompatible types • found : D1 • required: B • b = new D1(); • ^ • 1 error

14. Chapter 10 Getting Started with GUI Programming • GUI Class Hierarchy • Frames • Creating frames, centering frames, adding components to frames • Layout Managers • FlowLayout, GridLayout, BorderLayout • Drawing on Panels • The paintComponent method • Using Colors, Fonts, and Font Metrics • Drawing Geometric Figures • Lines, Rectangles, Ovals, Arcs, and Polygons • Event-Driven Programming • Event Source, Listener, Listener Interface

15. AWT/JFC • AWT was a powerful toolkit when introduced • it was the original driving force behind Java’s popularity • is today’s standard , a limited implementation • not designed to provide a serious, main UI for the needs of many programmers. • Now Swing, which has about four times the number of user interface (UI) components as the AWT • Swing is part of the standard Java distribution

16. AWT (Optional)

17. Question? • Is JFC and Swing the same?

18. JFC • Many programmer that that JFC and Swing are the same thing, but that’s not so; the JFC contains Swing and quite a number of other items.

19. What’s in JFC? Swing- The large UI package Cut and paste- Clipboard support Accessibility features- Aimed at users with disabilities. The desktop Colors features- First introduced in Java 1.1 Java2D- Improved color, image, and text support Printing- Originally enabled in Java 1.1

20. What’s in Swing? ClassDescription AbstractButton Abstract superclass for Swing buttons ButtonGroup Encapsulates a mutually exclusive set of buttons ImageIcon Encapsulates an icon JApplet The Swing version of Applet JButton The Swing push button class JCheckBox The Swing check box class JComboBox Encapsulates a combo box JLabel The Swing version of a label JRadioButton The Swing version of a radio button JScrollPane Encapsulates a scrollable window JTable Encapsulates a table-based control JTextField The Swing version of a text field JTree Encapsulates a tree-based control

21. GUI Class Hierarchy (Swing)

22. JComponent

23. JApplets • Fundamental to Swing is the JApplet class, which extends Applet. • Applets that use Swing must be subclasses of JApplet. • JApplet is rich with functionality that is not found in Applet. • For Example: • JApplet support various “panes”, such as the content pane, the glass pane, and the root pane.

24. Frames • Frame is a window that is not contained inside another window. Frame is the basis to contain other user interface components in Java GUI applications. • The Frame class can be used to create windows. • For Swing GUI programs, use JFrame class to create widows.

25. UI Components

26. Creating Frames • import javax.swing.*; • public class MyFrame { • public static void main(String[] args) { • JFrame frame = new JFrame("Test Frame"); • frame.setSize(400, 300); • frame.setVisible(true); • frame.setDefaultCloseOperation( • JFrame.EXIT_ON_CLOSE); • } • } NOTE: You must have JDK 1.3 or higher to run the slides. Run

27. Centering Frames By default, a frame is displayed in the upper-left corner of the screen. To display a frame at a specified location, you can use the setLocation(x, y) method in the JFrame class. This method places the upper-left corner of a frame at location (x, y).

28. Centering Frames, cont. Run

29. Adding Components into a Frame • // Add a button into the frame • frame.getContentPane().add( • new JButton("OK")); Run

30. NOTE The content pane is a subclass of Container. The statement in the preceding slide can be replaced by the following two lines: Container container = frame.getContentPane(); container.add(new JButton("OK")); You may wonder how a Container object is created. It is created when a JFrame object is created. A JFrame object uses the content pane to hold components in the frame.

31. Layout Managers • Java’s layout managers provide a level of abstraction to automatically map your user interface on all window systems. • The UI components are placed in containers. Each container has a layout manager to arrange the UI components within the container.

32. Kinds of Layout Managers • FlowLayout (Chapter 10) • GridLayout (Chapter 10) • BorderLayout (Chapter 10) • CardLayout (Chapter 12) • GridBagLayout (Chapter 12)

33. Example 10.1Testing the FlowLayout Manager The components are arranged in the container from left to right in the order in which they were added. When one row becomes filled, a new row is started. Run

34. FlowLayout Constructors • public FlowLayout(int align, int hGap, int vGap) Constructs a new FlowLayout with a specified alignment, horizontal gap, and vertical gap. The gaps are the distances inpixel between components. • public FlowLayout(int alignment) Constructs a new FlowLayout with a specified alignment and a default gap of five pixels for both horizontal and vertical. • public FlowLayout() Constructs a new FlowLayout with a defaultcenter alignment and a default gap of five pixelsfor both horizontal and vertical.

35. Example 10.2Testing the GridLayout Manager The GridLayout manager arranges componentsin a grid (matrix) formation with the number ofrows and columns defined by the constructor. The components are placed in the grid from left to right starting with the first row, then the second, and so on. Run

36. GridLayout Constructors • public GridLayout(int rows,int columns) Constructs a new GridLayout with the specified number of rows and columns. • public GridLayout(int rows, int columns, int hGap, int vGap) Constructs a new GridLayout with thespecified number of rows and columns,along with specified horizontal andvertical gaps between components.

37. Example 10.3Testing the BorderLayout Manager The BorderLayout manager divides the container into five areas: East, South, West, North, and Center. Components are added to a BorderLayout by using the add method. add(Component, constraint), where constraint is BorderLayout.EAST, BorderLayout.SOUTH, BorderLayout.WEST, BorderLayout.NORTH, or BorderLayout.CENTER. Run

38. Example 10.3, cont. Run

39. Using Panels as Containers • Panels act as smaller containers for grouping user interface components. • It is recommended that you place the user interface components in panels and place the panels in a frame. You can also place panels in a panel.

40. Example 10.4 Testing Panel This example uses panels to organize components. The program creates a user interface for a Microwave oven. Run

41. Drawing on Panels JPanel can be used to draw graphics (including text) and enable user interaction. To draw in a panel, you create a new class that extends JPanel and override the paintComponent method to tell the panel how to draw things. You can then display strings, draw geometric shapes, and view images on the panel.

42. Drawing on Panels, cont. public class DrawMessage extends JPanel { /** Main method */ public static void main(String[] args) { JFrame frame = new JFrame("DrawMessage"); frame.getContentPane().add(new DrawMessage()); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setSize(300, 200); frame.setVisible(true); } /** Paint the message */ public void paintComponent(Graphics g) { super.paintComponent(g); g.drawString("Welcome to Java!", 40, 40); } }

43. Drawing on Panels, cont.

44. NOTE The Graphics class is an abstract class for displaying figures and images on the screen on different platforms. The Graphics class is implemented on the native platform in the JVM. When you use the paintComponent method to draw things on a graphics context g, this g is an instance of a concrete subclass of the abstract Graphics class for the specific platform. The Graphics class encapsulates the platform details and enables you to draw things uniformly without concerning specific platforms.

45. NOTE Whenever a component is displayed, a Graphics object is created for the component. The Swing components use the paintComponent method to draw things. The paintComponent method is automatically invoked to paint the graphics context when the component is first displayed or whenever the component needs to be redisplayed. Invoking super.paintComponent(g) is necessary to ensure that the viewing area is cleared before a new drawing is displayed.

46. NOTE To draw things, normally you create a subclass of JPanel and override its paintComponent method to tell the system how to draw. In fact, you can draw things on any GUI component.

47. The Color Class You can set colors for GUI components by using the java.awt.Color class. Colors are made of red, green, and blue components, each of which is represented by a byte value that describes its intensity, ranging from 0 (darkest shade) to 255 (lightest shade). This is known as the RGB model. Color c = new Color(r, g, b); r, g, and b specify a color by its red, green, and blue components. Example: Color c = new Color(228, 100, 255);

48. Setting Colors You can use the following methods to set the component’s background and foreground colors: setBackground(Color c) setForeground(Color c) Example: setBackground(Color.yellow); setForeground(Color.red);

49. The Font Class Font myFont = Font(name, style, size); Example: Font myFont = new Font("SansSerif ", Font.BOLD, 16); Font myFont = new Font("Serif", Font.BOLD+Font.ITALIC, 12);

50. Finding All Available Font Names GraphicsEnvironment e = GraphicsEnvironment.getLocalGraphicsEnvironment(); String[] fontnames = e.getAvailableFontFamilyNames(); for (int i = 0; i < fontnames.length; i++) System.out.println(fontnames[i]);