Transcript
Computer Science Notes
Chapter 12: GUI Basics
These notes are meant to accompany Introduction to Java Programming: Brief Version, eighth edition by Y. Daniel Lang.
Book’s Statement of Skills:
To distinguish between Swing and AWT. (13.2)
To describe the Java GUI API hierarchy. (13.3)
To create user interfaces using frames, panels, and simple GUI components. (13.4)
To understand the role of layout managers. (13.5)
To use the FlowLayout, GridLayout, and BorderLayout managers to lay out components in a container. (13.5)
To specify colors and fonts using the Color and Font classes. (13.6 – 13.7)
To use JPanel as a subcontainer. (13.8)
To apply common features such as borders, tool tips, fonts, and colors on Swing components. (13.9)
To use borders to visually group user-interface components. (13.9)
To create image icons using the ImageIcon class. (13.10)
Section 12.1: Introduction
Section 12.2: Swing vs. AWT
Old Java GUI classes were bundled in a library called the Abstract Windowing Toolkit (AWT)
The AWT was prone to some bugs and only suitable for simple GUI applications.
AWT components rely heavily on the native GUI (i.e., the GUI that comes with the computer’s operating system)
AWT components are called heavyweight because of this native GUI dependence.
The AWT components were replaced by more robust and flexible components in the Swing library.
The Swing components have the same names as the AWT components except with a “J” in front of them.
Swing components do not depend on the native GUI, and are called lightweight because of that.
Section 12.3: The Java GUI API
The GUI API has three categories of objects: component classes, container classes, and helper classes
Component classes:
Section 12.3.1: Swing GUI Components
A component is an object having a graphical representation that can be displayed on the screen and that can interact with the user.
JComponent is the base class for all Swing components except top-level containers.
To use a component that inherits from JComponent, you must place the component in a containment hierarchy whose root is a top-level Swing container. Top-level Swing containers -- such as JFrame, JDialog, and JApplet -- are specialized components that provide a place for other Swing components to paint themselves.
Some JComponents discussed in the book are:
JButton (page 572)
JToggleButton (page 578)
JCheckBox (page 578)
JRadioButton (page 581)
JLabel (page 583)
JTextField (page 584)
JTextArea (page 586)
JComboBox (page 590)
JList (page 593)
JScrollBar (page 596)
JSlider (page 599)
JMenuBar and JMenu and JMenuItem – (not in book) An implementation of a menu bar. You add JMenu objects to the menu bar to construct a menu. When the user selects a JMenu object, its associated JPopupMenu is displayed, allowing the user to select one of the JMenuItems on it.
Section 12.3.2: Container Classes
An instance of the Container class can hold instances of the Component class.
Container classes are GUI components that are meant to contain other GUI components.
The AWT container classes are Window, Panel, Applet, Frame, and Dialog.
The Swing container classes are Container, JFrame, JDialog, JApplet, and JPanel.
java.awt.Container – is used to group components; its subclasses are frames, panels, and applets.
javax.swing.JFrame – is a window not contained in other windows. It is used to hold other Swing components.
javax.swing.JPanel – is an invisible container that holds other user-interface components. Panels can be nested. JPanel is often used as a canvas to draw graphics.
javax.swing.JApplet – is a subclass of Applet; you must extend JApplet to create a Swing-based Java applet.
javax.swing.JDialog – is a popup window or message box generally used as a temporary window to receive additional information or provide some kind of notification to the user.
Section 12.3.3: GUI Helper Classes
Helper classes are used to describe the properties of GUI components:
Graphics – is an abstract class that provides the methods for drawing lines, Strings, and simple shapes.
Color - encapsulates colors in the default sRGB color space. This class is used to specify foreground and background colors for container classes, or the colors of lines, shapes, and Strings in drawings
Font – specifies font properties (like font type, style, and size) for text and drawings on GUI components.
FontMetrics – an abstract class used to get the properties of the fonts
Dimension – encapsulates the width and height of a component (as integers) in a single object
LayoutManager – an interface that specifies methods for arranging components in a container
Section 12.4: Frames
javax.swing
Class JFrame
java.lang.Object
java.awt.Component
java.awt.Container
java.awt.Window
java.awt.Frame
javax.swing.JFrame
All Implemented Interfaces:
ImageObserver, MenuContainer, Serializable, Accessible, RootPaneContainer, WindowConstants
(Selected) Field Summary for JFrame
static int
EXIT_ON_CLOSE
The exit application default window close operation.
(Selected) Constructor Summary for JFrame
JFrame()
Constructs a new frame that is initially invisible.
JFrame(String title)
Creates a new, initially invisible Frame with the specified title.
(Selected) Method Summary for JFrame
int
getDefaultCloseOperation()
Returns the operation that occurs when the user initiates a "close" on this frame.
Graphics
getGraphics()
Creates a graphics context for this component.
JMenuBar
getJMenuBar()
Returns the menubar set on this frame.
protected boolean
isRootPaneCheckingEnabled()
Returns whether calls to add and setLayout are forwarded to the contentPane.
protected String
paramString()
Returns a string representation of this JFrame.
void
remove(Component comp)
Removes the specified component from the container.
void
repaint(long time, int x, int y, int width, int height)
Repaints the specified rectangle of this component within time milliseconds.
void
setDefaultCloseOperation(int operation)
Sets the operation that will happen by default when the user initiates a "close" on this frame.
void
setIconImage(Image image)
Sets the image to be displayed as the icon for this window.
void
setJMenuBar(JMenuBar menubar)
Sets the menubar for this frame.
void
setLayout(LayoutManager manager)
Sets the LayoutManager.
void
update(Graphics g)
Just calls paint(g).
(Selected) Method Summary for Frame
Image
getIconImage()
Returns the image to be displayed as the icon for this frame.
Rectangle
getMaximizedBounds()
Gets maximized bounds for this frame.
String
getTitle()
Gets the title of the frame.
void
setMaximizedBounds(Rectangle bounds)
Sets the maximized bounds for this frame.
void
setResizable(boolean resizable)
Sets whether this frame is resizable by the user.
void
setTitle(String title)
Sets the title for this frame to the specified string.
(Selected) Method Summary for Window
void
pack()
Causes this Window to be sized to fit the preferred size and layouts of its subcomponents.
void
paint(Graphics g)
Paints the container.
void
setMinimumSize(Dimension minimumSize)
Sets the minimum size of this window to a constant value.
void
setSize(Dimension d)
Resizes this component so that it has width d.width and height d.height.
void
setSize(int width, int height)
Resizes this component so that it has width width and height height.
void
setVisible(boolean b)
Shows or hides this Window depending on the value of parameter b.
(Selected) Method Summary for Container
Component
add(Component comp)
Appends the specified component to the end of this container.
Component
add(Component comp, int index)
Adds the specified component to this container at the given position.
void
doLayout()
Causes this container to lay out its components.
Component
getComponent(int n)
Gets the nth component in this container.
Component
getComponentAt(int x, int y)
Locates the component that contains the x,y position.
int
getComponentCount()
Gets the number of components in this panel.
Component[]
getComponents()
Gets all the components in this container.
LayoutManager
getLayout()
Gets the layout manager for this container.
T[]
getListeners(Class listenerType)
Returns an array of all the objects currently registered as FooListeners upon this Container.
Dimension
getMaximumSize()
Returns the maximum size of this container.
Dimension
getMinimumSize()
Returns the minimum size of this container.
Point
getMousePosition(boolean allowChildren)
Returns the position of the mouse pointer in this Container's coordinate space if the Container is under the mouse pointer, otherwise returns null.
Dimension
getPreferredSize()
Returns the preferred size of this container.
void
paint(Graphics g)
Paints the container.
void
paintComponents(Graphics g)
Paints each of the components in this container.
void
remove(Component comp)
Removes the specified component from this container.
void
remove(int index)
Removes the component, specified by index, from this container.
void
removeAll()
Removes all the components from this container.
void
setFont(Font f)
Sets the font of this container.
void
setLayout(LayoutManager mgr)
Sets the layout manager for this container.
void
update(Graphics g)
Updates the container.
protected void
validateTree()
Recursively descends the container tree and recomputes the layout for any subtrees marked as needing it (those marked as invalid).
Field Summary for Component
static float
BOTTOM_ALIGNMENT
Ease-of-use constant for getAlignmentY.
static float
CENTER_ALIGNMENT
Ease-of-use constant for getAlignmentY and getAlignmentX.
static float
LEFT_ALIGNMENT
Ease-of-use constant for getAlignmentX.
static float
RIGHT_ALIGNMENT
Ease-of-use constant for getAlignmentX.
static float
TOP_ALIGNMENT
Ease-of-use constant for getAlignmentY().
(Selected) Method Summary for Component
boolean
contains(int x, int y)
Checks whether this component "contains" the specified point, where x and y are defined to be relative to the coordinate system of this component.
boolean
contains(Point p)
Checks whether this component "contains" the specified point, where the point's x and y coordinates are defined to be relative to the coordinate system of this component.
void
doLayout()
Prompts the layout manager to lay out this component.
float
getAlignmentX()
Returns the alignment along the x axis.
float
getAlignmentY()
Returns the alignment along the y axis.
Color
getBackground()
Gets the background color of this component.
Rectangle
getBounds()
Gets the bounds of this component in the form of a Rectangle object.
Component
getComponentAt(int x, int y)
Determines if this component or one of its immediate subcomponents contains the (x, y) location, and if so, returns the containing component.
Component
getComponentAt(Point p)
Returns the component or subcomponent that contains the specified point.
Font
getFont()
Gets the font of this component.
FontMetrics
getFontMetrics(Font font)
Gets the font metrics for the specified font.
Color
getForeground()
Gets the foreground color of this component.
Graphics
getGraphics()
Creates a graphics context for this component.
int
getHeight()
Returns the current height of this component.
Point
getLocation()
Gets the location of this component in the form of a point specifying the component's top-left corner.
Point
getLocationOnScreen()
Gets the location of this component in the form of a point specifying the component's top-left corner in the screen's coordinate space.
Dimension
getMaximumSize()
Gets the maximum size of this component.
Dimension
getMinimumSize()
Gets the mininimum size of this component.
Dimension
getSize()
Returns the size of this component in the form of a Dimension object.
int
getWidth()
Returns the current width of this component.
int
getX()
Returns the current x coordinate of the components origin.
int
getY()
Returns the current y coordinate of the components origin.
void
paint(Graphics g)
Paints this component.
void
paintAll(Graphics g)
Paints this component and all of its subcomponents.
void
repaint()
Repaints this component.
void
repaint(int x, int y, int width, int height)
Repaints the specified rectangle of this component.
void
repaint(long tm, int x, int y, int width, int height)
Repaints the specified rectangle of this component within tm milliseconds.
void
setBackground(Color c)
Sets the background color of this component.
void
setBounds(int x, int y, int width, int height)
Moves and resizes this component.
void
setBounds(Rectangle r)
Moves and resizes this component to conform to the new bounding rectangle r.
void
setFont(Font f)
Sets the font of this component.
void
setForeground(Color c)
Sets the foreground color of this component.
void
setLocation(int x, int y)
Moves this component to a new location.
void
setLocation(Point p)
Moves this component to a new location.
void
setMaximumSize(Dimension maximumSize)
Sets the maximum size of this component to a constant value.
void
setMinimumSize(Dimension minimumSize)
Sets the minimum size of this component to a constant value.
void
setName(String name)
Sets the name of the component to the specified string.
void
setPreferredSize(Dimension preferredSize)
Sets the preferred size of this component to a constant value.
void
setSize(Dimension d)
Resizes this component so that it has width d.width and height d.height.
void
setSize(int width, int height)
Resizes this component so that it has width width and height height.
String
toString()
Returns a string representation of this component and its values.
void
update(Graphics g)
Updates this component.
Section 12.4.1: Creating a Frame
Use the JFrame class ( http://download.oracle.com/javase/6/docs/api/javax/swing/JFrame.html ).
See http://www.cs.armstrong.edu/liang/intro8e/html/MyFrame.html
Section 12.4.2: Adding Components to a Frame
Use the add method (inherited from the parent class Container) to add a component
See http://www.cs.armstrong.edu/liang/intro8e/html/MyFrameWithComponents.html
Use the remove method (inherited from the parent class Container) to remove a component
Section 12.5: Layout Managers
Layout managers are classes that control how components are added to a frame…
All layout managers implement the LayoutManager interface.
Layout managers are set in a container using the setLayoutManager() method.
Section 12.5.1: FlowLayout
Components are added from left to right in the order they are added.
See http://www.cs.armstrong.edu/liang/intro8e/html/ShowFlowLayout.html
Section 12.5.2: GridLayout
Components are added to a grid whose number of rows and columns is specified in the constructor.
See http://www.cs.armstrong.edu/liang/intro8e/html/ShowGridLayout.html
Section 12.5.3: BorderLayout
Components are added to one of five regions of the window: North, South, East, West, or Center.
See http://www.cs.armstrong.edu/liang/intro8e/html/ShowBorderLayout.html
Section 12.5.4: Properties of Layout Managers
The properties can be set dynamically… See the online documentation.
To change layouts, you must use a two-step process: first, use the setLayout(newLayout) method, then use the validate() method to force the container to re-draw the components
To update a current layout after changing its properties, use the doLayout() method
Section 12.6: Using Panels as Subcontainers
A JPanel object is usually used to contain a grouping of other components.
You can set the layout of a JPanel as well as add components…
See http://www.cs.armstrong.edu/liang/intro8e/html/TestPanels.html
Section 12.7: The Color Class
Colors are made of red, green, and blue components from 0 to 255 (the RGB model).
Example of creating a color object using the public Color(int r, int g, int b) constructor:
Color color1 = new Color(128, 100, 100);
The setBackground(Color c) and setForeground(Color c) methods (in the java.awt.Component class) can be used to change the colors of a component’s foreground or background.
There are 13 pre-defined standard colors…
Section 12.8: The Font Class
You can create a font using the java.awt.Font class and set fonts for components using the setFont method of the Component class.
The Font constructor is: public Font (String name, int style, int size);
Section 12.9: Common Features of Swing GUI Components
See http://www.cs.armstrong.edu/liang/intro8e/html/TestSwingCommonFeatures.html
Section 12.10: Image Icons
The ImageIcon class stores a small image for use as an icon
See http://www.cs.armstrong.edu/liang/intro8e/html/TestImageIcon.html
