Lecture 13: Dynamic Jlist and Drawing on JPanel

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Lecture 13 Dynamic Jlist and Drawing on JPanel

• Dynamic JLists
• To have a JList change during the execution of a
  program, we must deal with its underlying model,
  which contains the actual data.

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Lecture 13 Dynamic Jlist and Drawing on JPanel

• Example
• Create a model for a list
• DefaultListModel model new DefaultListModel()
• Create the list
• JList list new JList(model)
• Add items to the list by adding them to the model
• model.addElement("one")
• model.addElement("two")
• model.add(1, "oneandhalf")

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Lecture 13 Dynamic Jlist and Drawing on JPanel

• Remove items from the list by removing them from
  the model
• model.remove(0)
• model.removeElement("two")
• Size of list returned by
• model.getSize()
• Clear the list using
• model.clear()

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Lecture 13 Dynamic Jlist and Drawing on JPanel

• Drawing on a Panel
• An application that allows the user to draw on a
  panel.
• Application creates a panel on a frame for
  drawing.
• Uses Point class to save points.

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Lecture 13 Dynamic Jlist and Drawing on JPanel

• Variations of mouseDown
• Click
• Shift-click
• Double-click
• Uses of mouseDrag
• Draw a line (draw)
• Draw a filled oval (erase)

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Lecture 13 Dynamic Jlist and Drawing on JPanel

• Point Class

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public class java.awt.Point extends
java.lang.Object // Fields public int
x public int y // Constructors public
Point(int x, int y) // Methods public boolean
equals(Object obj) public void move(int x, int
y) public String toString() public void
translate(int dx, int dy)
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Lecture 13 Dynamic Jlist and Drawing on JPanel

• Note
• The drawing color can be set by two different
  methods
• setColor(Color c) in the class Graphics
• setForeground(Color c) in the class Component
• Doodle
• Add a DrawPanel, an inner class, to a frame.
• Capture mouse events to allow drawing on the
  panel.

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import java.awt. import java.awt.event. import
javax.swing. public class Doodle extends
JFrame Point lineStart new Point(0,0)
int circleSize 16 JPanel panel
Doodle() setTitle("Doodle")
addWindowListener(new WindowAdapter()
public void windowClosing(WindowEvent e)
System.exit(0) )
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panel new DrawPanel()
panel.setBackground(Color.cyan)
panel.addMouseListener(new Down())
panel.addMouseMotionListener(new Drag())
getContentPane().add(panel) class
DrawPanel extends JPanel public void
paintComponent(Graphics g)
super.paintComponent(g)
g.setColor(Color.blue)
g.drawString("Left button draws.",10,20)
g.drawString("Right button or shift-left
button erases.",10,35)
g.drawString("Double click clears
screen.",10,50)
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class Down extends MouseAdapter
public void mousePressed(MouseEvent e)
int x e.getX(), y e.getY()
if (e.isMetaDown() e.isShiftDown())
setForeground(panel.getBackground())
else setForeground(Color.blue)
if (e.getClickCount() 2) // double click
panel.repaint() else
lineStart.move(x,y)
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class Drag extends MouseMotionAdapter
public void mouseDragged(MouseEvent e)
int x e.getX(), y e.getY()
Graphics g getGraphics() if
(e.isMetaDown() e.isShiftDown())
g.fillOval(x-circleSize/2, y-circleSize/2,

circleSize, circleSize) else
g.drawLine(lineStart.x, lineStart.y, x, y)
lineStart.move(x,y)
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public static void main(String args)
JFrame jf new Doodle()
jf.setSize(600,500) jf.setVisible(true)

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Lecture 13 JTextArea

• JTextArea
• Constructors
• JTextArea(int rows, int cols)
• JTextArea(String text, int rows, int cols)

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Lecture 13 JTextArea

• Usage
• JTextArea ta new JTextArea("Message", 5, 20)
• ta.setEditable(false) // default is true
• ta.select(3,7)
• ta.selectAll()
• String s ta.getSelectedText()
• ta.setText("Replace all text")