Assignment 6

1
Section 11

• Assignment 6

2
Some engineering principles

• Design first, code later.
• Test, test, test. Use main in the tested classes
  to test them. Design a set of tests and run them
  all (grading guide for Assignment 2 can be a good
  example).
• Separation of content from presentation.

3
GUI - quick reminder

• JFrame - usually the main window. Can hold many
• JPanels - hold
• Components, i.e.
• JButton
• JTextFields
• many more
• using FlowLayouts to arrange them
• FlowLayout, GridLayout, ...

4
Example

• public class Ex extends JFrame
• public Ex()
• setTitle("Example 1")
• setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE)
  
• setSize(200, 200)
• getContentPane().setLayout(new FlowLayout())
• getContentPane().add(new JButton("OK"))
• setVisible(true)
• public static void main(String args)
• Ex e new Ex()

5
Events

• Event Objects sent by Components/Objects to other
  Objects.
• Source Components register listeners for its
  events.
• Listener objects must implement appropriate
  interfaces.

6
Example

• public class Ex1 extends JFrame implements
  ActionListener
• public Ex1()
• JButton bt new JButton("OK")
• setTitle("Example 1")
• setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE)
  
• setSize(200, 200)
• getContentPane().setLayout(new FlowLayout())
• bt.addActionListener(this)
• getContentPane().add(bt)
• setVisible(true)
• public void actionPerformed(ActionEvent e)
• if (e.getActionCommand().equals("OK"))
• System.out.println("Someone pressed the
  button!")
• public static void main(String args)

7
Example

• Design a Counter program
• Functionality
• Two buttons, one increments the value of the
  counter, the other decrements it.
• The value of the counter is displayed constantly.