gui
DESCRIPTION
GUI. Swing Class Hierarchy. Swing Components. Swing Conatiners. JFrame – top-level window to store components. Swing Conatiners. JPanel – container; can be embedded in JFrame. Layouts. FlowLayout arranges elements in a row elements centered by default within container GridLayout - PowerPoint PPT PresentationTRANSCRIPT
GUI
Swing Class Hierarchy
Swing Components
Swing Conatiners
JFrame – top-level window to store components
Swing Conatiners
JPanel – container; can be embedded in JFrame
Layouts
FlowLayout
arranges elements in a row
elements centered by default within container
GridLayout
subdivides container into cells of identical sizes
components take up all available space of a cell
BorderLayout
subdivides container into 5 areas: N, S, E, W, Center
Layouts
3x3 GridLayout 4x1 GridLayout BorderLayout
FlowLayout used to place the 3 panels in the Jframe.
Listeners Process events
ActionListener (JButton, Timer, JComboBox)
ChangeListener (JSlider)
MouseListener, MouseMotionListener
Listeners are interfaces; must implement ALL specified methods
ActionListener: void actionPerformed(ActionEvent e)
ChangeListener: void stateChanged(ChangeEvent e)
MouseListener: void mouseClicked(MouseEvent e)
void mousePressed(MouseEvent e)
void mouseReleased(MouseEvent e)
void mouseEntered(MouseEvent e)
void mouseExited(MouseEvent e)
MouseMotionListener: void mouseMoved(MouseEvent e) void mouseDragged(MouseEvent e)
Adapter classes Convenience classes
server as intermediaries between available interfaces (e.g. listeners) and the user defined classes (e.g. listeners)
make it possible to implement only the “important” methods
Adapter classes Convenience classes
server as intermediaries between available interfaces (e.g. listeners) and the user defined classes (e.g. listeners)
make it possible to implement only the “important” methods
abstract class MouseAdapter implements MouseListener, MouseMotionListener
{
void mousePressed(MouseEvent e) { // empty body }
void mouseReleased(MouseEvent e) { // empty body }
void mouseEntered(MouseEvent e) { // empty body }
void mouseExited(MouseEvent e) { // empty body }
void mouseMoved(MouseEvent e) { // empty body }
void mouseDragged(MouseEvent e) { // empty body }
}
MouseListener methods
MouseMotionListener methods
Adapter classes Convenience classes
server as intermediaries between available interfaces (e.g. listeners) and the user defined classes (e.g. listeners)
make it possible to implement only the “important” methods
abstract class MouseAdapter implements MouseListener, MouseMotionListener
{
abstract void mousePressed(MouseEvent e);
abstract void mouseReleased(MouseEvent e);
abstract void mouseEntered(MouseEvent e);
abstract void mouseExited(MouseEvent e);
abstract void mouseMoved(MouseEvent e);
asbtract void mouseDragged(MouseEvent e);
}
File IO
File IO PrintWriter – for writing to file; same methods as in System.out
Pretend that all output goes to screen
try { PrintWriter output = new PrintWriter(“input-file.txt”);
output.println(“Hello”);
output.printl(42);
output.println(“3.1459”);
output.close();
}
catch (Exception e) {
// report error
}
File IO Scanner – for reading from file; same as in CS111
Contents is viewed as a stream of characters
Reading stops as soon as appropriate token found; otherwise fails
try {
Scanner input = new Scanner(new File(“input-file.txt”));
String word = input.next();
int answer = input.nextInt();
double pi = input.nextDouble();
input.close();
}
catch (Exception e) {
// report error
}
Command-Line
Command Line Arguments Make it possible to send data to the program on execution
public static void main(String[] args)
{
System.out.println(“Parameters given on start-up:”);
System.out.println(“Number of params: “ + args.length);
for (int i = 0; i < args.length; i++) {
System.out.println(args[i]); // i-th parameter value }
}
Exceptions
Exceptions Mechanism for handling unexpected conditions (errors)
Force the programmer to handle error conditions
Allow for separating the logic of the code from error-handling
Sometimes no other option to report the value:
constructor
minElement, maxElement
Example – see FileIO
Exceptions Can create our own type of exception (should inherit from Exception)
class EmptyArrayException extends Exception
{
public void EmptyArrayException()
{
super();
}
public void EmptyArrayException(String message)
{
super(message);
}
}
Exceptions Example of our own Exception --- throw/throws
int minElement(int[] numbers) throws EmptyArrayException
{
// empty array --- throw an exception
if (numbers.length == 0)
{
throw EmptyArrayException(“Empty array given”);
}
//
// ... compute smallest element ...
//
}
extends vs. implements
class vs. interface
multiple inheritance
An interface specifies a collection of methods
An interface does not have data members or code for methods
A class that implements the interface must provide code (implementation) for all methods listed in the interface
interface RemoteControllable{
public void play();public void stop();public void ffwd();
}
class VCR implements RemoteControllable{ // must provide code for all methods in RemoteControllable}class DVD implements RemoteControllable{ // must provide code for all methods in RemoteControllable}
Interfaces
Multiple Inheritance
String name; //speciesvoid setName(String n) { ... ... ... }
String name; // pet’s namevoid setName(String n) { ... ... ... }
Class Mammal Class Pet
Class Cat
Multiple Inheritance
String name; //speciesvoid setName(String n) { ... ... ... }
String name; // pet’s namevoid setName(String n) { ... ... ... }
Class Mammal Class Pet
Which name is inherited?
Which setName() is inherited?
Class Cat
Complex rules required to disambiguate in multiple inheritance
Java does not support multiple inheritance; C++ does
Multiple Inheritance
String name; //speciesvoid setName(String n) { ... ... ... }
String name; // pet’s namevoid setName(String n) { ... ... ... }
Class Mammal Class Pet
Which name is inherited?
Which setName() is inherited?
Class Cat
What if we still want a Cat to behave like a Mammal and Pet
interface Mammal{ // all methods (behaviors) common to mammals // no code is specified, just the behavior names
(methods)}
class Pet{ // description of generic pet}
class Cat extends Pet implements Mammal{ // has all behaviors of a Pet – could override some
// must implement all behaviors of Mammal}
Multiple Inheritance
Can now use Cat objects anywhere Mammal behaviors required or where Pet objects are required
public void hunt(Mammal predator, Mammal prey){ // do something; could send a Cat as // either prey or predator}
public void doTricks(Pet pet){ // do something; could send a Cat for pet}
Multiple Inheritance
A Java class can only extend from one other class (single inheritance)
A Java class can implement multiple interfaces – can ambiguity arise?
Multiple Interfaces Implementation
A Java class can only extend from one other class (single inheritance)
A Java class can implement multiple interfaces – no ambiguity since
an interface cannot have data members
an interface cannot have code (implementation) for methods
Multiple Interfaces Implementation