Object Oriented Programming with JAVA

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• Object Oriented ProgrammingwithJAVA
• Graphical User Interface
• GUI
• Lecture 7

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Using Objects with Graphics

• import java.awt.
• import java.util..
• import javax.swing.
• class MyLine
• private int x1 // x coordinate of first endpoint
• private int y1 // y coordinate of first endpoint
• private int x2 // x coordinate of second
  endpoint
• private int y2 // y coordinate of second
  endpoint
• private Color myColor // color of this shape
• // constructor with input values
• public MyLine( int x1, int y1, int x2, int y2,
  Color color )
• this.x1 x1 // set x coordinate of first
  endpoint
• this.y1 y1 // set y coordinate of first
  endpoint
• this.x2 x2 // set x coordinate of second
  endpoint
• this.y2 y2 // set y coordinate of second
  endpoint
• myColor color // set the color
• // end MyLine constructor

// Draw the line in the specified color public
void draw( Graphics g ) g.setColor( myColor
) g.drawLine( x1, y1, x2, y2 ) // end
method draw // end class MyLine
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Using Objects with Graphics ,cont

• class DrawPanel extends JPanel
• private Random randomNumbers new Random()
• private MyLine lines // array of lines
• // constructor, creates a panel with random
  shapes
• public DrawPanel()
• setBackground( Color.WHITE )
• lines new MyLine 5 randomNumbers.nextInt( 5
  )
• // create lines
• for ( int count 0 count lt lines.length
  count )
• // generate random coordinates
• int x1 randomNumbers.nextInt( 300 )
• int y1 randomNumbers.nextInt( 300 )
• int x2 randomNumbers.nextInt( 300 )
• int y2 randomNumbers.nextInt( 300 )
• // generate a random color
• Color color new Color( randomNumbers.nextInt(
  256 ),
• randomNumbers.nextInt( 256 ), randomNumbers.nextIn
  t( 256 ) )
• // add the line to the list of lines to be
  displayed
• lines count new MyLine( x1, y1, x2, y2,
  color )

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Using Objects with Graphics ,cont

• // for each shape array, draw the individual
  shapes
• public void paintComponent( Graphics g )
• super.paintComponent( g )
• // draw the lines
• for ( MyLine line lines )
• line.draw( g )
• // end method paintComponent
• // end class DrawPanel
• public class TestDraw
• public static void main( String args )
• DrawPanel panel new DrawPanel()
• JFrame application new JFrame()
• application.setDefaultCloseOperation(
  JFrame.EXIT_ON_CLOSE )
• application.add( panel )
• application.setSize( 300, 300 )
• application.setVisible( true )
• // end main
• // end class TestDraw

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Displaying Text and Images in a Window

• import java.awt.FlowLayout // specifies how
  components are arranged
• import javax.swing.JFrame // provides basic
  window features
• import javax.swing.JLabel // displays text and
  images
• import javax.swing.SwingConstants // common
  constants used with Swing
• import javax.swing.Icon // interface used to
  manipulate images
• import javax.swing.ImageIcon // loads images
• //Youcan just use gt import java.swing.
• public class LabelTest
• public static void main( String args )
• LabelFrame labelFrame new LabelFrame() //
  create LabelFrame
• labelFrame.setDefaultCloseOperation(
  JFrame.EXIT_ON_CLOSE )
• labelFrame.setSize( 275, 180 ) // set frame size
• labelFrame.setVisible( true ) // display frame
• // end main
• // end class LabelTest

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Example cont

• class LabelFrame extends JFrame
• private JLabel label1 // JLabel with just text
• private JLabel label2 // JLabel constructed with
  text and icon
• private JLabel label3 // JLabel with added text
  and icon
• // LabelFrame constructor adds JLabels to JFrame
• public LabelFrame()
• super( "Testing JLabel" ) // to set title
• setLayout( new FlowLayout() ) // set frame
  layout
• //setLayout( new FlowLayout(FlowLayout.LEFT) )
  // left right . center
• // JLabel constructor with a string argument
• label1 new JLabel( "Label with text" )
• label1.setToolTipText( "This is label1" )
• // The tool tip text is displayed inside a
  colored rectangle. When the user //moves the
  mouse away, the tool tip is removed.
• add( label1 ) // add label1 to JFrame
• // JLabel constructor with string, Icon and
  alignment arguments

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Example cont

• label2 new JLabel( "Label with text and icon",
  bug, SwingConstants.LEFT )
• label2.setToolTipText( "This is label2" )
• add( label2 ) // add label2 to JFrame
• label3 new JLabel() // JLabel constructor no
  arguments
• label3.setText( "Label with icon and text at
  bottom" )
• label3.setIcon( bug ) // add icon to JLabel
• label3.setHorizontalTextPosition(
  SwingConstants.CENTER )
• label3.setVerticalTextPosition(
  SwingConstants.BOTTOM )
• label3.setToolTipText( "This is label3" )
• add( label3 ) // add label3 to JFrame
• // end LabelFrame constructor
• // end class LabelFrame

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9
JApplet

• An applet is a Java program that is meant to be
  embedded on a web page. When the applet is
  activated, the applet code is downloaded to the
  client's machine and executed
• Import javax.swing.JApplet. .

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Introduction to buttons, events, and
ActionListener

• Input from user can be done by mouse, keyboard,
  others.
• Two ways,
• Blocking mode.
• Event driven mode.
• Scanner scannew Scanner(System.in)
• scan.nextInt()
• Not feasible for GUI.

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Common java.awt.Component methods

• boolean isVisible() checks if this component is
  set to be visible. Components are initially
  visible, with the exception of top-level
  components such as JFrame.
• void setVisible(boolean b) shows or hides the
  component depending on whether b is true or
  false.
• boolean isEnabled() checks if this component is
  enabled. An enabled component can receive
  keyboard input. Components are initially enabled.

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Common java.awt.Component methods

• void setEnabled(boolean b) enables or disables
  a component.
• Point getLocation() returns the location of the
  top-left corner of this component, relative to
  the top-left corner of the surrounding container.
  (A Point object p encapsulates an x- and a
  ycoordinate which are accessible by p.x and p.y.)
• Point getLocationOnScreen() returns the
  location of the top-left corner of this
  component, using the screen's coordinates.
• void setBounds(int x, int y, int width, int
  height) moves and resizes this component. The
  location of the top-left corner is given by x and
  y, and the new size is given by the width and
  height parameters.

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Common java.awt.Component methods

• Dimension getSize() gets the current size of
  this component.
• void setSize(int width, int height) and
• void setSize(Dimension d) resizes the component
  to the specified width and height.

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Ex Handling buttons

• import javax.swing.
• import java.awt.
• import java.awt.event. // must be
• public class ButtonTest
• public static void main(String args)
• MyFrame xnew MyFrame()
• enum EventTypeCLOSE, HELLO
• class MyFrame extends JFrame
• public MyFrame()
• initializeComponents()
• setSize(WIDTH, HEIGHT)
• setVisible(true)

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Ex Handling buttons , cont

• void initializeComponents()
• setLayout(new FlowLayout())
• //hello button
• btnHellonew JButton("Hello")
• btnHello.addActionListener(new myListener(EventTyp
  e.HELLO))
• add(btnHello)
• //close button
• btnClosenew JButton("Close")
• btnClose.addActionListener(new myListener(EventTyp
  e.CLOSE))
• add(btnClose)
• JButton btnClose
• JButton btnHello
• final int WIDTH300
• final int HEIGHT300

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Ex Handling buttons , cont..

• class myListener implements ActionListener
• EventType action
• public myListener(EventType action)
• this.actionaction
• public void actionPerformed(ActionEvent event)
  // function in interface
• switch(action)
• case HELLO
• JOptionPane.showMessageDialog(null,"Hello events
  world")
• break
• case CLOSE
• System.exit(0)

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JFrame

• Some common used methods inside the JFrame are
• The setTitle method for changing the text in
  the title bar
• The setResizable method, which takes a boolean
  to determine if a frame will be resizeable by the
  user.
• The setLocation(x, y) sets the top-left corner
  of the frame relative to the desktop origin.
• The setBounds(x, y, width, height) lets you
  resize and relocate a component in one step

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JFrame structure.

• The structure of a JFrame is very complex.
• Four panes are layered in a JFrame
• The root pane
• layered pane
• glass pane are of no interest to us
• They are required to organize the menu bar
  and content pane and to implement the look and
  feel.
• The part that most concerns Swing programmers
  is the content pane. When designing a frame, you
  add components into the content pane.

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JFrame structure.
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Text Fields

• a single-line area in which the user can enter
  text via the keyboard.
• JTextField
• JPasswordField
• Methods commonly used
• setText(String)
• String getText()
• setToolTipText(String)
• private JTextField textField1 // text field with
  set size
• textField1 new JTextField( 10 )
• textField1.setText("initial")
• String s textField1.getText()
• JOptionPane.showMessageDialog( null, s)
• textField1.setToolTipText(" text field")

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Text field Example

• import java.awt.
• import java.awt.event.
• import javax.swing.
• class TextFieldFrame extends JFrame
• private JTextField textField1 // text field with
  set size
• private JTextField textField2 // text field
  constructed with text
• private JTextField textField3 // text field with
  text and size
• private JPasswordField passwordField // password
  field with text
• // TextFieldFrame constructor adds JTextFields to
  JFrame
• public TextFieldFrame()
• super("Testing JTextField and JPasswordField" )
• setLayout( new FlowLayout() ) // set frame
  layout
• // construct textfield with 10 columns
• textField1 new JTextField( 10 )
• add( textField1 ) // add textField1 to JFrame
• // construct textfield with default text
• textField2 new JTextField( "Enter text here" )

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Text field Example , cont..

• add( textField2 ) // add textField2 to JFrame
• // construct textfield with default text and 21
  columns
• textField3 new JTextField( "Uneditable text
  field", 21 )
• textField3.setEditable( false ) // disable
  editing
• add( textField3 ) // add textField3 to JFrame
• // construct passwordfield with default text
• passwordField new JPasswordField( "Hidden text"
  )
• add( passwordField ) // add passwordField to
  JFrame
• // register event handlers
• TextFieldHandler handler new TextFieldHandler()
  
• textField1.addActionListener( handler )
• textField2.addActionListener( handler )
• textField3.addActionListener( handler )
• passwordField.addActionListener( handler )
• // end TextFieldFrame constructor

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• // private inner class for event handling
• private class TextFieldHandler implements
  ActionListener
• // process text field events
• public void actionPerformed( ActionEvent event )
• String string "" // declare string to display
• // user pressed Enter in JTextField textField1
• if ( event.getSource() textField1 )
• string String.format( "textField1 s",
• event.getActionCommand() )
• // user pressed Enter in JTextField textField2
• else if ( event.getSource() textField2 )
• string String.format( "textField2 s",
• event.getActionCommand() )
• // user pressed Enter in JTextField textField3
• else if ( event.getSource() textField3 )
• string String.format( "textField3 s",
• event.getActionCommand() )
• // user pressed Enter in JTextField passwordField
• else if ( event.getSource() passwordField )

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Text field Example , cont..

• public class TextFieldTest
• public static void main( String args )
• TextFieldFrame textFieldFrame new
  TextFieldFrame()
• textFieldFrame.setDefaultCloseOperation(
  JFrame.EXIT_ON_CLOSE )
• textFieldFrame.setSize( 325, 150 ) // set frame
  size
• textFieldFrame.setVisible( true ) // display
  frame
• // end main
• // end class TextFieldTest

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Strings

• length() returns the length of the string
• charAt(i) returns the character at index I
• , also concat(str) for concatenation
• format(), like printf, it returns a formated
  string
• String fs
• fs String.format("The value of the float
  variable is " "f, while the value of the
  integer " "variable is d, and the string "
  "is s", floatVar, intVar, stringVar)
• System.out.println(fs)

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Strings cont.

• To convert strings to numbers, use the number
  subclass parseyyyy(str) method.
• float a Float.parseFloat(23.56)
• int b Integer.parseInt(203)
• To convert number to string you use the number
  subclass method toString()
• int i
• double d
• String s3 Integer.toString(i)
• String s4 Double.toString(d)
• you can also use concatenation int i4
  String si

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String Useful methods
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String Useful methods, cont
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String Useful methods, cont
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Strings Example

• public class Filename
• private String fullPath
• private char pathSeparator, extensionSeparator
• public Filename(String str, char sep, char ext)
• fullPath str
• pathSeparator sep
• extensionSeparator ext
• public String extension()
• int dot fullPath.lastIndexOf(extensionSeparator)
  
• return fullPath.substring(dot 1)
• public String filename() // gets filename
  without extension
• int dot fullPath.lastIndexOf(extensionSeparator)
  
• int sep fullPath.lastIndexOf(pathSeparator)
• return fullPath.substring(sep 1, dot)
• public String path()
• int sep fullPath.lastIndexOf(pathSeparator)

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Strings Example

• public class FilenameDemo
• public static void main(String args)
• final String FPATH "/home/mem/index.html"
• Filename myHomePage new Filename(FPATH,'/',
  '.')
• System.out.println("Extension
  "myHomePage.extension())
• System.out.println("Filename "
  myHomePage.filename())
• System.out.println("Path " myHomePage.path())