1

Języki Programowania

Graficzny interfejs użytkownika

2

GUI Principles



GUI

– Graphical User Interface



GUI’s are a good target for OO design



GUI’s main elements



Components

: GUI building blocks.



buttons, menus, sliders, etc.



Layout

: arranging components to

form a usable GUI.



using layout managers.



Events

: reacting to user input.



button presses, menu selections, etc.

 There are some tools for convenient GUI-based design



JBuilder, Eclipse, NetBeans

2

3

Java GUI classes



AWT

(Abstract Window Toolkit) (java.awt.*)

 pierwszy szkielet GUI dla Javy (Java 1.1)


pewne uzależnienia o implementacji języka



problemy implementacji na różnych platformach



Swing

(javax.swing.*)

 kolejne GUI wprowadzone od wersji Java 1.2
 zawiera cechy AWT i dodatkowe rozszerzenia


poprawione komponenty (bez uzależnienia się od implementacji)



mechanizmy do zmiany GUI w czasie działania programu



SWT

(Standard Widget Toolkit; from Eclipse)

4

AWT and Swing

AWT

was the original platform-dependent layer of

Java to build GUI’s.

Swing

(platform independent layer) was added later.

Swing is part of JFC (

Java Framework Collection

).

3

5

Event-driven programming

- sterowanie zdarzeniami

 GUIs are

event-driven programs

: external events cause

methods to be executed



Components (komponenty)

: objects we create which

have a screen presence (e.g. controls, window panes),
and with which the user interacts (e.g. buttons).



Events (zdarzenia)

: when a user interacts with a

component, java creates an event object (which records
the source)



Listeners

(„słuchacze”)

: Objects we create which

respond to events. A listener has a handler method,
which Java invokes when the event occurs.

6

Container (window) with
component (button)

All this for one button click ...

user

user clicks
button

event object
is generated

ae:ActionEvent

event is
queued
for action

Listener objects

... do something

pętla obsługi

zdarzeń

: remove from

queue, invoke

handlers in

registered

listeners

4

7

... which requires:

 In the program:

 write a class that creates a window and a

JButton

, adds the

JButton to the window, makes the window visible

 write listener classes (implements

ActionListener

) with handler

method (ActionPerformed)

 create listener objects and register them with the JButton

 At runtime:

 user clicks the button
 Java creates the ActionEvent object
 Java adds object to a queue of events
 Java repeatedly



takes object from queue



identifies their listeners



invokes each listener's handler with event as input

8

A first GUI ...

import

java.awt.*;

import

java.awt.event.*;

import

javax.swing.*;

public

class

SimplePanel

extends

JPanel {

private

JButton btn;

public

SimplePanel() {

super

();

btn =

new

JButton("Click me!");

add(btn);
ActionListener lstnr =

new

SimpleButtonListener();

btn.addActionListener(lstnr);
}

import AWT, AWT.event
and Swing packages

call to JPanel constructor

create a button

add it to the panel

create a listener

register it with the button

5

9

public

static

void

main(String[] args) {

JFrame frm =

new

JFrame("A simple GUI");

Container contentPane = frm.getContentPane();
JPanel pnl =

new

SimplePanel();

contentPane.add(pnl);
frm.setBounds(100, 300, 400, 200);
frm.setVisible(true);
}

}

SimplePanel continued

create a frame

get a handle on it

create a panel

add panel to frame

position it on screen

make it visible!

10

SimpleButtonListener

import

java.awt.event.*;

public class

SimpleButtonListener

implements

ActionListener {

private

int

count;

public

SimpleButtonListener() {

}

public

void

actionPerformed(ActionEvent ae) {

count++;
System.out.println(count);
}
}

tell Java it
is a Listener

state what happens
when the button is
pressed

6

11

That’s it ...

try do it in BlueJ yourself

you can also use JDK ...

no changes in source code needed

after 10 clicks

12

Components in the GUI

 the GUI needs 2

JButto

ns

, a subclass of

JPanel

,

and



javax.swing.JTextField



allows display / entry / edit of a line of text



constructor specifies initial value (and number of columns)



has methods

setText(...), getText(...),

etc.



javax.swing.JLabel



allows display of text / images



user cannot edit them



constructor supplies initial text



has methods

setText(...), getText(...),

etc.

7

13

JFrame

JPanel (in the ContentPane
of the JFrame)

JButton

JTextField

JLabel

Components in the GUI

14

GUI Containers

 some components are

containers



can have other components added to them

 JPanel

is a container

– it has

JButton

s added to it



a container can have other containers added to it

 JFrame

is a container

– it has a

JPanel

added to it (via its

content pane)

 (in fact, in Swing, all components are containers)

8

15

1. The Window Listener

 we mentioned that we could associate a listener with the

JFrame

 the WindowListener interface specifies 7 methods, which

respond to changes in a window's state:

 windowActivated(...)

: window is set to be active

 windowClosed(...)

: window is closed by program

 windowClosing(...)

: window closed by user

 windowDeactivated(...)

: window is no longer active

 windowDeiconified(...)

: window is restored to normal

 windowIconified(...)

: window is minimised

 windowOpened(...)

: window opened for first time

16

2. Using WindowAdapter

 instead of laboriously typing default methods for the

WindowListener

, we can instead inherit from

WindowAdapter

:



implements

WindowListener



supplies 7 default methods

 all we need to do is override the particular methods we

want

9

17

Good news for GUI developers



Even simple GUI seems to be very complicated to
develop in Java



Fortunetely, we have a number of IDEs (

Integrated

Development Environments

) to do it using a mouse and

„drag and pop” method

 JBuilder (from

Borland

)

 JCreator
 Eclipse
 NetBeans (

Sun Microsystems

)

18

NetBeans