Transcript Getting started with BlueJ

First BlueJ Day
Houston, 2006
David J. Barnes
University of Kent
Getting started with BlueJ
• My personal route to using BlueJ
• Traditional approaches to teaching
Java and OOP
• The problems
• How BlueJ addresses the problems
First BlueJ Day, Houston, Texas, 1st March 2006
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My personal route
•
•
•
•
Looking for an OO language
Blue at SIGCSE 1997
Java by decree
Objects early via the command
line.
– Prentice-Hall textbook in 2000
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Traditional approaches to
teaching Java
• Strong influence of procedural
programming
• Heavy dependence on textbooks.
• ‘Hello world’
• GUI-based
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Hello World
A necessary starting point?
public class Hello
{
public static void main(String[] args)
{
System.out.println("Hello, world");
}
}
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Text output
public class OldMacDonald
{
public static void main(String[] args)
{
System.out.println("Old MacDonald had a farm");
System.out.println("E I E I O");
System.out.println("and on his farm he had a duck");
System.out.println("E I E I O");
System.out.println("With a quak quak here");
System.out.println("And a quak quak there");
System.out.println("Here a quak, there a quak");
System.out.println("Everywhere a quak quak");
System.out.println("Old MacDonald had a farm");
System.out.println("E I E I O");
}
}
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Text input and output
import java.util.Scanner;
public class Square
{
public static void main(String[] args)
{
Scanner reader = new Scanner(System.in);
System.out.print("Input a number: ");
int number = reader.nextInt();
System.out.println(number + " squared is " +
(number * number));
}
}
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Classes to wrap functions
Data Fields
Conversion:
square metres
to square yards
for a piece of
fabric
sqMeters
Methods
toSqYards
readSqMeters
displayFabric
getDouble
displayResult
...
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GUIs
import java.awt.*;
public class Message extends Frame {
Font f;
public Message() {
f = new Font("SansSerif", Font.BOLD, 24);
setBackground(Color.yellow);
setSize(400, 150); setVisible(true);
}
public void paint(Graphics g) {
g.setFont(f);
g.setColor(Color.blue);
g.drawString("Welcome to Java", 100, 100);
}
}
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GUIs (continued)
public class FirstApp extends wheel.users.Frame {
private wheels.users.Ellipse _ellipse;
public FirstApp() {
_ellipse = new wheels.users.Ellipse();
}
// magic to let the FirstApp execute
public static void main(String[] args) {
FirstApp app = new FirstApp();
}
}
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The problems
• Java’s main method is a
requirement.
• Traditional (procedural) curricula
exert a strong influence.
• GUI-based examples are
attractive, but often carry a lot of
baggage.
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What I would like to teach
• Classes and objects from day 1
• Object fundamentals
– state
– behaviour
– multiplicity
– independence
• Let students experience objects
• Emphasise modelling
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Avoiding the problems
•
•
•
•
Jump start
Don't use main
Don't start with I/O
Beware the complexities of GUIs
– custom libraries may have potential
• Pick early examples very carefully
– avoid simply converting old examples
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What does BlueJ have to
offer?
• Liberation from a main method
• A visual and interactive
environment that is simple to use
• An environment that supports OO
concepts
– the opportunity to experience objects
– access to object state and behaviour
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Using BlueJ – first steps
Shapes and Pictures
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Next steps
• Avoid teaching BlueJ
– BlueJ is a means to support OO
teaching.
• Choose examples that illustrate
key concepts
• Beware of falling back into old
ways
• Avoid the completeness trap
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Next steps (continued)
• Don't be afraid to use 'large'
examples
– Encourage students to read code
– Apprenticeship is appropriate
• Use sensible examples
• Avoid giving them a blank screen
– Design is hard
– Syntax can be a stumbling block
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Summary
• Teaching proper OO may require a
radical rethink of material
• BlueJ provides excellent support
for a truly OO curriculum
• OO is possible from day 1 –
‘objects first’
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