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.

Grid Layout

3x3 GridLayout 4x1 GridLayout BorderLayoutGridLayout layout = new GridLayout(3, 3);panel.setLayout(layout);

button1 = new JButton( "1" );panel.add( button1 );

button2 = new JButton( "2" );panel.add( button2 );

button3 = new JButton( "3" );panel.add( button3 );

button4 = new JButton( "4" );panel.add( button4 );

... ... ... ... ...

Components are stretched to occupy the whole panel area.

Border Layout

3x3 GridLayout 4x1 GridLayout BorderLayoutBorderLayout layout = new BorderLayout();panel.setLayout(layout);

button1 = new JButton( "North" );panel.add( button1, BorderLayout.NORTH );

button2 = new JButton( "South" );panel.add( button2, BorderLayout.SOUTH );

button3 = new JButton( "East" );panel.add( button3, BorderLayout.EAST );

button4 = new JButton( "West" );panel.add( button4, BorderLayout.WEST );

button5 = new JButton( "Center" );panel.add( button5, BorderLayout.CENTER );

Center area gets most of the space. The other areas are given only as much as they need. Not all areas need to be occupied.

Listeners Process events from components, containers

ActionListener (JButton, Timer, JComboBox)

ChangeListener (JSlider)

MouseListener, MouseMotionListener (JPanel, JFrame)

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 the available interfaces and the user-defined (listener) classes that implement the interfaces

make it possible to implement only the methods of interest

Adapter classes Convenience classes

server as intermediaries between the available interfaces and the user-defined (listener) classes that implement the interfaces

make it possible to implement only the methods of interest

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 the available interfaces and the user-defined (listener) classes that implement the interfaces

make it possible to implement only the methods of interest

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);

}

Adapter classes Convenience classes

server as intermediaries between the available interfaces and the user-defined (listener) classes that implement the interfaces

make it possible to implement only the methods of interest

abstract class MouseAdapter implements MouseListener, MouseMotionListener

{

… … … … … … … … … … … … …

}

class LineListener extends MouseAdapter

{

… implement only the methods of interest …

}

File IO

Text File Output PrintWriter used for writing to file; same methods as in System.out

As if output is written to the screen with the extra steps of opening a file, closing the file, and catching exceptions

try { PrintWriter output = new PrintWriter("output-file.txt");

output.println("Hello");

output.printl(42);

output.println(3.1459);

output.close();

} catch (Exception e) {

// report error

}

Text File Input Scanner used for reading from file; same as in CS111

As if input is received from the keyboard with the extra steps of opening a file, closing the file, and catching exceptions

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

}

Need to know the file format

Whitespaces are ignored

Serialization Mechanism for making exact copies of objects

For simple classes enough to declare implements Serializable

Application – saving / reading actual objects from a file

Saving with Serialization ObjectOutputStream and method writeObject(obj)

try {

FileOutputStream file = new FileOutputStream("pets.ser");

ObjectOutputStream output = new ObjectOutputStream(file);

output.write(petsList.size());

for (Pet pet : petsList) {

output.writeObject(pet);

}

output.close();

}catch (Exception e) {

System.out.println("Could not write to file. " + e);

}

ObjectInputStream and method readObject()

try {

FileInputStream file = new FileInputStream("pets.ser");

ObjectInputStream output = new ObjectInputStream(file);

int count = input.readInt();

for (int i = 0; i < count; i++) {

Pet pet = input.readObject();

}

output.close();

}catch (Exception e) {

System.out.println("Could not read from file. " + e);

}

Reading with Serialization

Exceptions

Exceptions Mechanism for handling unexpected RUN-TIME 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

Interfaces 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}

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