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Painting and Events in Java
Packages
Class framework
Windows, Painting, Events
Java Platform (JDK)
1
• The Java Platform includes extensive crossplatform libraries to do everything from threading
to database queries to user-interfaces.
Java Class Library
2
• Classes are grouped into packages (i.e.
namespaces) to avoid name collisions.
• To assign your source code to a package,
use the package keyword at the top of
source files.
• Typically, package = subdirectory
– e.g. “graphics” package is in subdirectory of
the same name
– alt. it can be included in a JAR file.
• Use the import keyword to include a class
from a different package in your code.
– This is how you include bundled Java
libraries.
3
Common Classes/Packages
Java Class Hierarchy
4
Package
Classes
(Examples)
Description
java.awt
Color, Graphics,
Graphics2D, event.
Contains all of the classes for
creating user interfaces and for
painting graphics and images.
javax.swing
JFrame, JButton,
JList, JToolbar
Provides a set of "lightweight" (allJava language) components that
works the same on all platforms.
java.io
File, FileReader,
FileWriter,
InputStream
Provides for system input and output
through data streams, serialization
and the file system.
java.lang
Boolean, Integer,
String, System,
Thread, Math
Provides classes that are
fundamental to the design of the
Java programming language.
java.util
ArrayList, HashMap,
Observable
Contains the collections framework,
legacy collection classes, event
model,…
Java 8 API Specification:
https://docs.oracle.com/javase/8/docs/api/overview-summary.html
• Implicit class hierarchy
– All classes in Java are derived from the Object class in
java.lang defines and implements common class
behavior
• e.g. clone(), toString(), finalize() methods
– Classes you write inherit this basic behavior.
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Getting Started
Creating a window
Painting
Events
6
Open a Window
package guis_1.v1;
import javax.swing.*;
public class GUIs1v1 {
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
@Override
public void run() {JFrame is a container for components.
Paint on components (coming).
JFrame frame = new JFrame("Window Title");
frame.setDefaultCloseOperation(
JFrame.EXIT_ON_CLOSE);
frame.setSize(400, 500);
frame.setVisible(true);
}
}
}
});
Open a Window
7
package guis_1.v1;
import javax.swing.*;
public class GUIs1v1 {
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
@Override
public void run() {
JFrame frame = new JFrame("Window Title");
frame.setDefaultCloseOperation(
JFrame.EXIT_ON_CLOSE);
frame.setSize(400, 500);
frame.setVisible(true);
}
}
}
});
invokeLater ensures that the program
can’t start accepting events from the
user before it’s ready to start processing
them.
Swing Component Hierarchy
8
• java.awt.Window is the base for all containers.
• javax.swing.Jcomponent is the root for all widgets.
9
Adding a Component
package guis_1.v2;
import javax.swing.*;
public class GUIs1v2 {
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
@Override
public void run() {
JFrame frame = new JFrame("Window Title");
frame.setDefaultCloseOperation(
JFrame.EXIT_ON_CLOSE);
frame.setSize(400, 500);
}
}
}
});
frame.add(new ColouredX());
frame.setVisible(true);
class ColouredX extends JComponent {
}
Painting the ColouredX
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class ColouredX extends JComponent {
private BasicStroke stroke = new BasicStroke(30.0f);
public void paintComponent(Graphics g) {
Graphics vs.
Graphics2D g2 = (Graphics2D) g;
Graphics2D
int w = this.getWidth();
int h = this.getHeight();
paintComponent is called
automatically. You never
g2.setStroke(this.stroke);
call it yourself.*
g2.setRenderingHint(
RenderingHints.KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON);
g2.setColor(Color.RED);
g2.drawLine(0, 0, w, h);
g2.setColor(Color.BLUE);
g2.drawLine(0, h, w, 0);
}
}
*Except, maybe, for pedagogical
reasons in part 1 of assignment 1.
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Responding to Events
12
Responding to Events (Painful)
class ColouredX extends JComponent {
private BasicStroke stroke = new BasicStroke(30.0f);
private LinkedList<Point> clicks =
List of clicked points.
new LinkedList<Point>();
public ColouredX() {
this.addMouseListener(
new ColouredXMouseListener(this));
}
public void addClick(Point p) {
this.clicks.add(p);
this.repaint();
}
Add a clicked point
to the list.
repaint()…
public void paintComponent(Graphics g) {
Graphics2D g2 = (Graphics2D) g;
this.paintX(g2);
g2.setColor(Color.BLACK);
for (Point p : this.clicks) {
g2.drawString("click", p.x, p.y);
}
Paint the clicked points.
}
public void paintX(Graphics2D g) { ... }
}
Responding to Events (Painful)
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class ColouredXMouseListener implements MouseListener {
private ColouredX cx;
public ColouredXMouseListener(ColouredX cx) {
this.cx = cx;
}
@Override
public void mouseClicked(MouseEvent e) {
this.cx.addClick(e.getPoint());
}
@Override
public void mousePressed(MouseEvent e) { }
@Override
public void mouseReleased(MouseEvent e) { }
}
@Override
Must implement
public void mouseEntered(MouseEvent
e)all{five
} methods
named in the MouseListener
@Override
interface in spite of only needing one.
public void mouseExited(MouseEvent e) { }
Responding to Events (Less Painful)
14
class ColouredXMouseListener extends MouseAdapter {
private ColouredX cx;
public ColouredXMouseListener(ColouredX cx) {
this.cx = cx;
}
@Override
public void mouseClicked(MouseEvent e) {
this.cx.addClick(e.getPoint());
}
}
ColouredX class
remains the same.
15
Every listener interface with more than
one method has a corresponding adapter
– an abstract class with an empty
method for each method in the interface.
Just override the relevant methods.
Responding to Events (Better)
class ColouredX extends JComponent {
...
private LinkedList<Point> clicks =
public ColouredX() {
this.addMouseListener(
new ColouredXMouseListener());
}
new LinkedList<Point>();
An inner class has
access to private
members in the
enclosing class.
class ColouredXMouseListener extends MouseAdapter {
@Override
public void mouseClicked(MouseEvent e) {
ColouredX.this.clicks.add(e.getPoint());
repaint();
}
Changes to ColouredXMouseListener:
}
1. Ref to ColouredX is gone.
2. Constructor is gone; no need to pass argument.
public void paintComponent(Graphics g) {
...
Changes to ColouredX:
}
1. addClick is gone; content moved to mouseClicked
}
Responding to Events (Ideomatic)
16
class ColouredX extends JComponent {
...
private LinkedList<Point> clicks =
new LinkedList<Point>();
public ColouredX() {
this.addMouseListener(
new MouseAdapter() {
@Override
public void mouseClicked(MouseEvent e) {
clicks.add(e.getPoint());
repaint();
}
}
Anonymous inner class: Java’s
);
equivalent to passing a function.
}
public void paintComponent(Graphics g) {
...
}
}
17
Animation in Java
18
Animation using a Timer
class ColouredX
...
private Point
private final
private Timer
extends JComponent {
ballPos = new Point(100, 0);
int FPS = 40;
FPS = Frames Per Second
timer;
public ColouredX() {
this.addMouseListener(...);
javax.swing.Timer
this.timer =
new Timer(1000/FPS, new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
ballPos.y += 2;
repaint();
}
});
this.timer.start();
}
19
}
public void paintComponent(Graphics g) {
Paint the ball at
...
its new location.
g2.setColor(Color.ORANGE);
g2.fillOval(this.ballPos.x, this.ballPos.y, 30, 30);
}