Programming
language 2
Java GUI – part 1
Loredana STANCIU
loredana.stanciu@upt.ro
Room B616
What is a user interface
That part of a program that interacts with the user of the
program:
simple command-line interfaces
point-and-click graphical user interfaces
A common set of tools for graphical user interface design
that work on a variety of platforms
A user interface toolkit called the Abstract Windowing
Toolkit, or the AWT
Components and containers
A graphical user interface is built of graphical elements
called components: buttons, scrollbars, and text fields
Components do not stand alone, but rather are found
within containers.
Contain and control the layout of components
Components and containers
Components must fit completely within the
container
Creates a tree of elements, starting with the
container at the root of the tree and expanding out
to the leaves
GUI – Graphical User interface
Types of components
Types of components
Button
Button()
Creates a button
Button(String label)
Creates a labeled button
void addActionListener(ActionListener l)
Adds the specified action listener to receive
action events from this button.
Button
String getLabel()
Gets the label of the current button.
void setLabel(String label)
Sets the button's label to be the specified string.
Button — example
You can create a button by creating an
instance of the Button class:
Button buttonOne = new Button();
Button buttonOne = new Button("This is a
button");
You can add a button to a frame by using the
add() method:
aFrame.add(buttonOne);
CheckBox
A graphical component that can be in either an
"on" (true) or "off" (false) state.
setLayout(new GridLayout(3, 1));
add(new Checkbox("one", null, true));
add(new Checkbox("two"));
add(new Checkbox("three"));
CheckBox
Checkbox()
Creates a check box with no label
Checkbox(String label)
Creates a check box with the specified label
Checkbox(String label, boolean state)
Creates a check box with the specified label
and sets the specified state
Checkbox(String label,
CheckboxGroup group, boolean state,)
Creates a check box with the label, set to the
state, and in the check box group
CheckBox
void addItemListener (ItemListener l)
Adds the specified item listener to receive
item events from this check box.
String getLabel()
Gets the label of this check box.
Boolean getState()
Determines whether this check box is in the
"on" or "off" state
CheckBox
void setCheckboxGroup(CheckboxGroup g)
Sets this check box's group to be the
specified check box group.
void setLabel(String label)
Sets this check box's label to be the string
argument.
void setState(boolean state)
Sets the state of this check box to the specified
state.
CheckboxGroup
Used to group together a set of Checkbox
buttons.
Exactly one check box button in a
CheckboxGroup can be in the "on" state at any
given time
Pushing any button sets its state to "on" and
forces any other button that is in the "on" state
into the "off" state
CheckboxGroup — Example
setLayout(new GridLayout(3, 1));
CheckboxGroup cbg = new CheckboxGroup();
add(new Checkbox("one", cbg, true));
add(new Checkbox("two", cbg, false));
add(new Checkbox("three", cbg, false));
Chioce
A pop-up menu of choices. The current choice is
displayed as the title of the menu.
Choice ColorChooser = new Choice();
ColorChooser.add("Green");
ColorChooser.add("Red");
ColorChooser.add("Blue");
Chioce
Choice()
Creates a new choice menu.
void add(String item)
Adds an item to this Choice menu.
void addItemListener(ItemListener l)
Adds the specified item listener to receive
item events from this Choice menu.
String getItem(int Index)
Gets the string at the specified index in this
Choice menu.
Chioce
int getItemCount()
Returns the number of items in this Choice
menu.
int getSelectedIndex()
Returns the index of the currently selected
item.
String getSelectedItem()
Gets a representation of the current choice
as a string.
Chioce
void insert(String item, int index)
Inserts the item into this choice at the
specified position.
void remove(int position)
Removes an item from the choice menu at
the specified position.
void remove(String item)
Removes the first occurrence of item from the
Choice menu.
Chioce
void removeAll()
Removes all items from the choice menu.
void select(int position)
Sets the selected item in this Choice menu to
be the item at the specified position.
void select(String str)
Sets the selected item in this Choice menu to
be the item whose name is equal to the
specified string.
Label
A component for placing text in a container.
Displays a single line of read-only text.
setLayout(new
FlowLayout(FlowLayout.CENTER, 10, 10));
add(new Label("Hi There!"));
add(new Label("Another Label"));
Label
Label(String text);
Creates a new instance of Label
String getText();
Returns a label’s text
void setText(String text);
Sets a label’s text to the specified text
Scrollbar
Provides a convenient means for allowing a user to
select from a range of values.
redSlider=new
Scrollbar(Scrollbar.VERTICAL, 0, 1, 0,
255);
add(redSlider);
ranger = new
Scrollbar(Scrollbar.HORIZONTAL, 0, 60, 0,
300);
add(ranger);
Scrollbar
Scrollbar()
Constructs a new vertical scroll bar.
Scrollbar(int orientation)
Constructs a new scroll bar with the specified
orientation.
Scrollbar
Scrollbar(int orientation, int value,
int visible, int minimum, int maximum)
Constructs a new scroll bar with the specified
orientation, initial value, visible amount, and
minimum and maximum values.
void addAdjunstmentListener(Adjust
mentListener l)
Adds the specified adjustment listener to receive
instances of AdjustmentEvent from this scroll
bar.
TextField
A text component that allows for the editing of a
single line of text.
TextField tf1, tf2, tf3, tf4;
tf1 = new TextField();
tf2 = new TextField("", 20);
tf3 = new TextField("Hello!");
tf4 = new TextField("Hello", 30);
TextField
TextField()
Creates a new instance of TextField
TextField(String text)
Creates a new instance of TextField with
the specified text
void setColumns(int columns)
Sets the number of columns in a textbox
void setText(String text)
Sets a textfield text to the specified text
List
A scrolling list of text items. The list can be set up
so that the user can choose either one item or
multiple items.
List lst = new List(4, false);
lst.add("Mercury"); lst.add("Venus");
lst.add("Earth"); lst.add("JavaSoft");
lst.add("Mars"); lst.add("Jupiter");
lst.add("Saturn"); lst.add("Uranus");
lst.add("Neptune"); lst.add("Pluto");
List
List()
Creates a new scrolling list.
List(int row)
Creates a new scrolling list initialized with the
specified number of visible lines.
List(int rows, boolean multipleMode)
Creates a new scrolling list initialized to display
the specified number of rows.
List
void add(String item)
Adds the specified item to the end of scrolling
list.
void add(String item, int index)
Adds the specified item to the the scrolling list
at the position indicated by the index.
void addActionListener(ActionListener l)
Adds the specified action listener to receive
action events from this list.
List
void remove( int position)
Removes the item at the specified position
from this scrolling list.
void remove( String item)
Removes the first occurrence of an item from
the list.
void removeAll()
Removes all items from this list.
List
void replaceItem(String value, int
index)
Replaces the item at the specified index in
the scrolling list with the new string.
void select(int index)
Selects the item at the specified index in the
scrolling list.
TextArea
A multi-line region that displays text.
It can be set to allow editing or to be read-only.
new TextArea("Hello", 5, 40);
TextArea
TextArea(int rows, int columns)
Constructs a new text area with the specified
number of rows and columns and the empty
string as text.
TextArea(String text)
Constructs a new text area with the specified
text.
TextArea(String text, int rows, int
columns)
Constructs a new text area with the specified
text, and with the specified number of rows and
columns.
TextArea
TextArea(String text, int rows, int
columns, int scrollbars)
Constructs a new text area with the specified
text, and with the rows, columns, and scroll bar
visibility as specified.
void append(String str)
Appends the given text to the text area's
current text.
void insert(String str, int position)
Inserts the specified text at the specified
position in this text area.
Types of containers
Window
A top-level display surface (a window)
An instance of the Window class has no border
and no title
Frame
A top-level display surface (a window) with a
border and title
An instance of the Frame class may have a
menu bar
Types of containers
Dialog
A top-level display surface (a window) with a
border and title
An instance of the Dialog class cannot exist
without an associated instance of the Frame
class.
Panel
A generic container for holding
components.
An instance of the Panel class provides a
container to which to add components.
FRAMES
A top-level window with a title and a border.
It has minimize, maximize, and close buttons in its
top right corner and can be moved and resized
(by default)
Frames are created using the Frame class
FRAMES
Frame()
Creates a new instance of Frame that is
initially invisible
Frame(String title)
Creates a new instance of Frame that is
initially invisible with the specified title
NOTE: Initially, a frame will not be visible. You
have to set it to be visible using the
setVisible() method
FRAMES
boolean isResizable()
Returns a boolean value indicating whether a
frame is resizable or not
void setResizable(boolean resizable)
Sets whether or not a frame is resizable
void isVisible(boolean isVisible)
Sets whether or not a frame is visible
FRAMES
String getTitle()
Returns the title of a frame
void setTitle(String title)
Sets the title of a frame
void setSize(int width, int height)
Sets the size of a frame
void setLocation(int xCoord, int
yCoord)
Sets the location of the window
Frames
Frames are capable of generating the following
types of WindowEvents:
WINDOW_OPENED
WINDOW_CLOSING
WINDOW_CLOSED
WINDOW_ICONIFIED
WINDOW_DEICONIFIED
WINDOW_ACTIVATED
WINDOW_DEACTIVATED
WINDOW_GAINED_FOCUS
WINDOW_LOST_FOCUS
WINDOW_STATE_CHANGED
Frames — Example
You can create a frame creating an instance of
class Frame:
import java.awt.*;
class MyFrame {
public static void main(){
Frame frame = new Frame("My
title");
frame.setSize(200, 200);
frame.setVisible(true);
}}
Dialog
A top-level window with a title and a border that
is typically used to take some form of input from
the user.
The size of the dialog includes any area
designated for the border.
A dialog must have either a frame or another
dialog defined as its owner when it's constructed.
Dialog
Dialog(Dialog owner)
Constructs an initially invisible, non-modal
Dialog with an empty title and the specified
owner dialog.
Dialog(Dialog owner, String title)
Constructs an initially invisible, non-modal
Dialog with the specified owner dialog and
title.
Dialog(Frame owner)
Constructs an initially invisible, non-modal
Dialog with an empty title and the specified
owner frame.
Dialog
Dialog(Frame owner, String title)
Constructs an initially invisible, non-modal
Dialog with the specified owner frame and
title.
String getTitle()
Gets the title of the dialog.
void hide()
Hides the Dialog and then causes show() to
return if it is currently blocked.
Dialog
void show()
Makes the Dialog visible.
void setResizable(boolean resizable)
Sets whether this dialog is resizable by the
user.
void setTitle(String title)
Sets the title of the Dialog.
Panel
The simplest container class
Provides space in which an application can
attach any other component, including other
panels.
The default layout manager for a panel is the
FlowLayout layout manager.
Panel
Panel()
Creates a new panel using the default layout
manager.
Panel(LayoutManager layout)
Creates a new panel with the specified
layout manager.
void add(…)
Add a component to the panel
void remove(…)
Remove a component from the panel
Java event handling
Event handling in Java refers to executing some
code when specific actions occur such as a
window being minimized or a button being
clicked
There are special interfaces for this purpose and
they are located in the java.awt.event package
Handling window events
To handle window events, the WindowListener
interface is used
The class that handle window events must
implement this interface
The WindowListener interface has various
methods to handle window events
These methods are presented on the following
slides
Methods of the
WindowListener interface
windowOpened(WindowEvent e)
Called when a window first becomes visible
windowActivated(WindowEvent e)
Called when a window has become active
(meaning it is able to accept input events)
windowDeactivated(WindowEvent e)
Called when a window is deactivated
(meaning it has lost input focus)
Methods of the
WindowListener interface
windowIconified(WindowEvent e)
Called when a window is iconified (minimized)
windowDeiconified(WindowEvent e)
Called when a window has been restored from a
minimized state
windowClosing(WindowEvent e)
Called when a user attempts to close a frame
windowClosed(WindowEvent e)
Called when a window is closed
Handling action events
To handle action events (such as the clicking of
a button), the ActionListener interface is used
Method of the ActionListener interface:
actionPerformed(ActionEvent e)
Called when an action has occurred
Handling focus events
To handle focus events (such as when an object
such as a textbox is awaiting user input), the
FocusListener interface is used
Methods of the FocusListener interface:
focusGained(FocusEvent e)
Called when an object gains focus
focusLost(FocusEvent e)
Called when an object loses focus
Handling item events
Item events are triggered by components that
allow for a selection of items such as
Checkboxes
To handle item events, the ItemListener
interface is used
Method of the ItemListener interface:
itemStateChanged(ItemEvent e)
Called when the state of an item has
changed
Handling text events
Text events are triggered by components whose
fields are editable such as textboxes
To handle text events, the TextListener
interface is used
Method of the TextListener interface:
textValueChanged(TextEvent e)
Called when the data in a field of a
component has changed
Handling mouse events
Mouse events are triggered by the computers
mouse
Mouse events are actually handled by two
interfaces:
MouseListener: used to detect the
clicking of mouse buttons or the moving of a
mouse into or out of a listener's area
MouseMotionListener: used to detect the
movement of the mouse
Methods of the
MouseListener interface
mouseClicked(MouseEvent e)
Called when a mouse button is clicked
mouseEntered(MouseEvent e)
Called when the mouse enters a source
components area
Methods of the
MouseMotionListener interface
mouseMoved(MouseEvent e)
Called when the mouse is moved while in a
components area
mouseDragged(MouseEvent e)
Called when the mouse moves while a mouse
button is down while within a components area
Handling key events
Key events are triggered by keyboard actions
Key events are handled by the KeyListener
interface
Methods of the KeyListener interface:
keyPressed(KeyEvent e)
Called when a key is pressed down
keyReleased(KeyEvent e)
Called when a key is released
keyTyped(KeyEvent e)
Called when a key is typed
Making objects listen for
events
Once you implement the necessary interfaces,
and define the implementation of their methods,
you need to make objects listen for events
Example: if you implement the ActionListener
interface, and you define what its
actionPerformed() method does, and you
want the method to be called every time a
certain button is clicked, you need to make that
button listen for the event
Listen for action events
For action events use the addActionListener()
method
Example:
//create a button
Button aButton = new Button("This is a
button");
//specify that this button listens for
action events
aButton.addActionListener(this);
Listen for action events
The class that contains the previous button must
implement the interface ActionListener, so it
will have a function
actionPerformed(ActionEvent e)
You can find the source of this event calling the
function e.getSource()
This function will return an element of type
Object
Listen for focus events
For focus events use the addFocusListener()
method
Example:
//create a textbox
TextField aTextField = new TextField("This
is a textbox");
/*specify that this textbox listens for
focus events*/
aTextField.addFocusListener(this);
Listen for item events
For item events use the addItemListener()
method
Example:
//create a checkbox
CheckBox chkbox1 = new CheckBox("This is a
checkbox", false);
/*specify that this checkbox listens for
item events*/
chkbox1.addItemListener(this);
Listen for text events
For text events use the addTextListener()
method
Example:
//create a textbox
TextField aTextField = new TextField("This
is a textbox");
/*specify that this textbox listens for
text events*/
aTextField.addTextListener(this);
Listen for mouse events
For mouse events use the addMouseListener()
method
Example:
//create a frame
Frame aFrame = new Frame();
/*specify that this frame listens for
mouse events*/
aFrame.addMouseListener(this);
Listen for mouse motion
events
For mouse motion events use the
addMouseMotionListener() method
Example:
//create a frame
Frame aFrame = new Frame();
/*specify that this frame listens for
mouse motion events*/
aFrame.addMouseMotionListener(this);
Listen for key events
For key events use the addKeyListener()
method
Example:
//create a textbox
TextField aTextField = new TextField("This
is a textbox");
/*specify that this textbox listens for
key events*/
aTextField.addKeyListener(this);
References
Todd Sundsted, Introduction to the AWT. A
description of Java’s user interface toolkit,
http://www.javaworld.com/javaworld/jw-07-
1996/jw-07-awt.html
