GUI programming

1. GUI programming • AWT(Abstract Windows Toolkit)-GUI components library when Java was introduced • AWT was replaced by Swing components • import javax.swing.*;

2. GUI API class hierarch – p371 Object Dimension,Font, FontMetrics, Color, Graphics, Component LayoutManager, Container Panel, Window, Jcomponent Applet, Frame, Dialog

3. GUI – Container classes • Container classes are GUI components that are used as containers to contain other GUI components • Container, JFrame, JDialog, JApplet, and JPanel

4. Java GUI API – container classes • Container: used to group components. A layout manager is used to position and place components in a container • Frames, panels and applets are examples of containers • JFrame: window not contained inside another window. It is the container that holds other Swing user-interface components • JDialog: popup window or message box • JApplet: subclass of Applet. You must extend JApplet to create a Swing-based Java applet. • JPanel: invisible container that holds user-interface components. Panel can be nested. JPanle also can be used as a canvas to draw graphics

5. GUI helper classes • Helper classes are not subclass of Component. They are used to describe the properties of GUI components • Graphics: abstract class that provides a graphical context for drawing strings, lines, and simple shapes • Color: deals with colors of GUI components • Font: specifies fonts for the text and drawings on GUI components • FontMetrics is an abstract class used to get the properties of the font • Dimension: encapsulates the width and height of a component • LayoutManager: specify how components are arranged in a container

6. Frame • Create a Frame • import javax.swing.*; • public class MyFrame{ • public static void main( String[] args){ • JFrame frm = new JFrame(“Test Frame”); • frm.setSize(400, 300); • frm.setVisible(true); • frm.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); • } • }

7. Centering a Frame • To display the frame at specific location -up left corner at (x,y) • frm.setLocation(x,y); • Centering a frame • Dimension screen = Toolkit.getDefaultToolkit().getScreenSize(); • int width = screen.width; • int height = screen.height; • Dimension frmsize = frm.getSize(); • int x = (width – frmsize.width)/2; • int y = (height – frmsize.height)/2;

8. Adding components to a frame • Container container = frm.getContentPane(); • JButton btn_ok = new JButton(“OK”); • container.add(btn_ok);

9. Layout Managers • FlowLayout is the simplest layout manager. The components are arranged in the container from left to right in the order in which they were added • public FlowLayout(int align, int hgap, int vgap) – construct a new FlowLayout with the specified alignment, horizontal gap and vertical gap. • public FlowLayout( int alignment) – with Hgap and vGap 5 pixels • public FlowLayout() – center alignment and 5 pixels gaps.

10. GridLayout • The GridLayout manager arranges components in a grid with number of rows and columns defined by the constructor. • public GridLayout(int rows, int columns, int hgap, int vgap) • public GridLayout(int rows, int columns)- 0 gaps • public GridLayout() – one column in a single row

11. The number of row or column can be zero but not both; • If 0 rows and 3 columns for a grid with 10 components, GridLayout creates 3 columnds and 4 rows • If both the number of rows and columns are nonzero, the number of rows is the dominating parameter; that is, the number of rows is fixed, and the layout manager dynamically calculate the number of columns.

12. example • Container container = getContentPane(); • container.setLayout(new FlowLayout(FlowLayout.LEFT,10,20)); • container.setLayout(new GridLayout(4,3,10,20)); • for( int I = 0; I < 10; I++) • { • container.add(new Jbutton(“Component”+I); • }

13. BorderLayout • The BorderLayout manager divides the window into five areas: • East, South, West, North and Center • public BorderLayout(int hgap, int vgap) • public BorderLayout – construct a new BorderLayout without horizontal or vertical gaps • North and south can stretch horizontally • West and east can stretch vertocally • Center can stretch both horizontally and vertically to fill any empty space • Components are added to a BorderLayout by using add(component, index), where index is a constant BorderLayout.East, South, North, and West

14. panel • You can divide window into panels • Panels can act like smaller container to group user-interface components • You can add button in a panel and add the panel into the frame. • You also can use layout manger to set layout of components I the panel

15. panel • Create a panel and add buttons to the panel; • Panel p1 = new Panel(); • p1.setLayout(new GridLayout(3,3)); • p1.add(new Button(“OK”); • Add the panel to the container • container.add(p1);

16. Color class – java.awt.Color • Colors are made of red, green and blue, each of which is represented by a byte value 0(darkest)-255(lightest), known as RGB model • Constructor: • public Color( int r, int g, int b) • Color color = new Color(128, 100,100); • JButton jbtOK = new JButton(“OK”); • jbtOK.setBackground(color); • Jbt.setForeground(new Color(100,1,1));

17. Alternative • You can use one of 13 standard colors • black, blue, cyan, darkGray, gray, green, lightGray, magenta, orange, pink, red, white, yellow • They are defined as constants in java.awt.Color • jbtOK.setForeground(Color.red);

18. Font class – java.awt.Font • Constructor: • public Font(String name, int style, int size); • You can choose a font name from • SansSerif, Serif, Monospaced, Dialog, or DialogInput • You can choose a style from • Font.PLAIN, Font.BOLD, Font.ITALIC and Font.BOLD + Font.ITALIC • Specify a font size of any positive integer. • Font font1 = new Font(“SansSerif”, Font.BOLD, 16); • Font font2 = new Font(“Serif”, Font.BOLD+Font.ITALIC, 12); • JButton jbtOK = new JButton(“OK”); • jbtOK.setFont(font1);