Chapter 9. The java.awt Package

ActiveEvent	Java 1.2
java.awt

This interface is implemented by events that know how to dispatch themselves. When the event dispatch system encounters an ActiveEvent on the event queue, it simply invokes the dispatch() method of the event, instead of attempting to dispatch the event on its own. This interface is implemented by java.awt.event.InvocationEvent, which is used by the invokeLater() and invokeAndWait() methods of EventQueue.

Implementations: java.awt.event.InvocationEvent

Adjustable	Java 1.1
java.awt	PJ1.1

This interface defines the methods that should be implemented by an object that maintains a user-adjustable numeric value. The adjustable value has specified minimum and maximum values, and it may be incremented or decremented either a unit at a time or a block at a time. An Adjustable object generates an AdjustmentEvent when it is adjusted and maintains a list of AdjustmentListener objects interested in being notified when such an event occurs.

This interface abstracts the essential functionality of the Scrollbar and javax.swing.JScrollBar components.

Implementations: Scrollbar, javax.swing.JScrollBar

Passed To: java.awt.event.AdjustmentEvent.AdjustmentEvent(), java.awt.peer.ScrollPanePeer.{setUnitIncrement(), setValue()}

Returned By: ScrollPane.{getHAdjustable(), getVAdjustable()}, java.awt.event.AdjustmentEvent.getAdjustable()

AlphaComposite	Java 1.2
java.awt

This implementation of the Composite interface blends colors according to their levels of alpha transparency. AlphaComposite does not have a public constructor, but you can obtain a shared immutable instance by calling the static getInstance() method, specifying the desired compositing rule (one of the eight integer constants defined by the class), and specifying an alpha value. Alternatively, if you use an alpha value of 1.0, you can simply use one of the eight predefined AlphaComposite constants. Once you have obtained an AlphaComposite object, you use it by passing it to the setComposite() method of a Graphics2D object.

The most common way to use an AlphaComposite object is to specify the SRC_OVER compositing rule and an alpha value greater than 0 but less than 1. This causes the source colors you draw to be given the specified level of alpha transparency, so that they are blended with whatever colors already exist on the screen, making the destination colors appear to show through the translucent source colors. This technique allows you to achieve transparency effects using opaque colors when you are drawing onto a drawing surface, like a screen, that does not have an alpha channel.

The other compositing rules of AlphaComposite are best understood when both the source (your drawing) and the destination (the drawing surface) have alpha channels. For example, you can create translucent Color objects with the four-argument version of the Color() constructor, and you can create an off-screen image with an alpha channel by passing the constant TYPE_INT_ARGB to the java.awt.image.BufferedImage() constructor. (Once your compositing operation has been performed in an off-screen image with an alpha channel, you can view the results by copying the contents of the image to the screen, of course.) When your source and destination have alpha channels built in, you do not usually specify an alpha value for the AlphaComposite itself. If you do, however, the transparency values of the source colors are multiplied by this alpha value.

AlphaComposite supports the following compositing rules:

SRC

Replace the colors of the destination with the colors of the source, ignoring the destination colors and the transparency of the source.

SRC_OVER

Combine the source and destination colors combined based on the transparency of the source, so that the source appears to be drawn over the destination.

DST_OVER

Combine the source and destination colors based on the transparency of the destination, so that the source appears to be drawn underneath the destination.

SRC_IN

Draw the colors of the source using the transparency values of the destination, completely ignoring the colors of the destination.

SRC_OUT

Draw the colors of the source using the inverse transparency values of the destination.

DST_IN

Modify the colors of the destination using the alpha values of the source and ignoring the colors of the source.

DST_OUT

Modify the colors of the destination using the inverted alpha values of the source and ignoring the colors of the source.

CLEAR

Ignore the color and transparency of both the destination and the source. This clears the destination by making it a fully transparent black.

Hierarchy: Object-->AlphaComposite(Composite)

Returned By: AlphaComposite.getInstance()

Type Of: AlphaComposite.{Clear, DstIn, DstOut, DstOver, Src, SrcIn, SrcOut, SrcOver}

AWTError	Java 1.0
java.awt	serializable error PJ1.1

Signals that an error has occurred in the java.awt package.

Hierarchy: Object-->Throwable(Serializable)-->Error-->AWTError

AWTEvent	Java 1.1
java.awt	serializable event PJ1.1

This abstract class serves as the root event type for all AWT events in Java 1.1 and supersedes the Event class that was used in Java 1.0.

Each AWTEvent has a source object, as all EventObject objects do. You can query the source of an event with the inherited getSource() method. The AWTEvent class adds an event type, or ID, for every AWT event. Use getID() to query the type of an event. Subclasses of AWTEvent define various constants for this type field.

The various _MASK constants are used by applets and custom components that call the enableEvents() method of Component to receive various event types without having to register EventListener objects.

Hierarchy: Object-->java.util.EventObject(Serializable)-->AWTEvent

Subclasses: java.awt.event.ActionEvent, java.awt.event.AdjustmentEvent, java.awt.event.ComponentEvent, java.awt.event.InputMethodEvent, java.awt.event.InvocationEvent, java.awt.event.ItemEvent, java.awt.event.TextEvent, javax.swing.event.AncestorEvent, javax.swing.event.InternalFrameEvent

Passed To: Too many methods to list.

Returned By: Component.coalesceEvents(), EventQueue.{getNextEvent(), peekEvent()}

AWTEventMulticaster	Java 1.1
java.awt	PJ1.1

AWTEventMulticaster is a convenience class used when writing a custom AWT component. It provides an easy way to maintain a list of AWT EventListener objects and notify the listeners on that list when an event occurs.

AWTEventMulticaster implements each of the event listener interfaces defined in the java.awt.event package, which means that an AWTEventMulticaster object can serve as any desired type of event listener. (It also means that the class defines quite a few methods.) AWTEventMulticaster implements what amounts to a linked list of EventListener objects. When you invoke one of the EventListener methods of an AWTEventMulticaster, it invokes the same method on all of the EventListener objects in the linked list.

Rather than instantiate an AWTEventMulticaster object directly, you use the static add() and remove() methods of the class to add and remove EventListener objects from the linked list. Calling add() or remove() returns an AWTEventMulticaster with the appropriate EventListener object registered or deregistered. Using an AWTEventMulticaster is somewhat non-intuitive, so here is some example code that shows its use:

public class MyList extends Component {   // a class that sends ItemEvents
  // The head of a linked list of AWTEventMulticaster objects
  protected ItemListener listener = null;
  public void addItemListener(ItemListener l) {      // add a listener
    listener = AWTEventMulticaster.add(listener, l);
  }
  public void removeItemListener(ItemListener l) {   // remove a listener
    listener = AWTEventMulticaster.remove(listener, l);
  }
  protected void fireItemEvent(ItemEvent e) {        // notify all listeners
    if (listener != null) listener.itemStateChanged(e);
  }
  // The rest of the class goes here
}

Hierarchy: Object-->AWTEventMulticaster(java.awt.event.ActionListener(java.util.EventListener),java.awt.event.AdjustmentListener(java.util.EventListener),java.awt.event.ComponentListener(java.util.EventListener),java.awt.event.ContainerListener(java.util.EventListener),java.awt.event.FocusListener(java.util.EventListener),java.awt.event.InputMethodListener(java.util.EventListener),java.awt.event.ItemListener(java.util.EventListener),java.awt.event.KeyListener(java.util.EventListener),java.awt.event.MouseListener(java.util.EventListener),java.awt.event.MouseMotionListener(java.util.EventListener),java.awt.event.TextListener(java.util.EventListener),java.awt.event.WindowListener(java.util.EventListener))

AWTException	Java 1.0
java.awt	serializable checked PJ1.1

Signals that an exception has occurred in the java.awt package.

Hierarchy: Object-->Throwable(Serializable)-->Exception-->AWTException

Thrown By: Cursor.getSystemCustomCursor()

AWTPermission	Java 1.2
java.awt	serializable permission

This class encapsulates permissions for performing various AWT-related operations; applications do not typically use it. The name, or target, of a permission should be one of the following values: "accessClipboard", "accessEventQueue", "listenToAllAWTEvents", or "showWindowWithoutWarningBanner". Alternatively, a name of "*" implies all of these values. AWTPermission does not use actions, so the actions argument to the constructor should be null.

Hierarchy: Object-->java.security.Permission(java.security.Guard,Serializable)-->java.security.BasicPermission(Serializable)-->AWTPermission

BasicStroke	Java 1.2
java.awt

This class defines properties that control how lines are drawn. By default, lines are one-pixel wide and solid. To change these attributes, pass a BasicStroke (or another implementation of Stroke) to the setStroke() method of a Graphics2D object. BasicStroke supports the following line attribute properties:

lineWidth

The thickness of the line.

endCap

The end cap style of the line. CAP_BUTT specifies that a line ends exactly at its end points, without caps. CAP_SQUARE causes a line to end with square caps that extend beyond the end points by a distance equal to one-half of the line width. CAP_ROUND specifies that a line ends with round caps with a radius of one-half of the line width.

lineJoin

The join style when two line segments meet at the vertex of a shape. JOIN_MITER specifies that the outside edges of the two line segments are extended as far as necessary until they intersect. JOIN_BEVEL causes the outside corners of the vertex to be joined with a straight line. JOIN_ROUND specifies that the vertex is rounded with a curve that has a radius of half the line width.

miterLimit

The maximum length of the miter used to connect two intersecting line segments. When two lines intersect at an acute angle and the line join style is JOIN_MITER, the length of the miter gets progressively longer as the angle between the lines gets smaller. This property imposes a maximum length on the miter; beyond this length, the miter is squared off.

dashArray

The pattern of dashes and spaces that make up a dashed line. This attribute is an array, where the first element and all the additional odd elements specify the lengths of dashes. The second element and all the additional even elements specify the lengths of the spaces. When the dash pattern is complete, it starts over at the beginning of the array, of course.

dashPhase

The distance into the dash pattern that line drawing begins. Note that this value is not an index into the dash array, but a distance. For example, if you've specified a dash of length 5 followed by a space of length 3 and want to begin your line with the space rather than the dash, you set this property to 5.

See Stroke for a discussion of how line drawing is performed in Java 2D.

Hierarchy: Object-->BasicStroke(Stroke)

BorderLayout	Java 1.0
java.awt	serializable layout manager PJ1.1

A LayoutManager that arranges components that have been added to their Container (using the Container.add() method) with the names "North", "South", "East", "West", and "Center". These named components are arranged along the edges and in the center of the container. The hgap and vgap arguments to the BorderLayout constructor specify the desired horizontal and vertical spacing between adjacent components.

In Java 1.1, five constants were defined to represent these strings. In Java 1.2, an additional four constants have been added to represent the four sides of the container in a way that is independent of writing direction. For example, BEFORE_LINE_BEGINS is the same as WEST in locales where text is drawn from left to right, but is the same as EAST in locales where text is drawn from right to left.

Note that an application should never call the LayoutManager methods of this class directly; the Container for which the BorderLayout is registered does this.

In Java 1.1, five constants were defined to represent these strings. In Java 1.2, an additional four constants have been added to represent the four sides of the container in a way that is independent of writing direction. For example, BEFORE_LINE_BEGINS is the same as WEST in locales where text is drawn from left to right but is the same as EAST in locales where text is drawn right to left.

Hierarchy: Object-->BorderLayout(LayoutManager2(LayoutManager),Serializable)

Button	Java 1.0
java.awt	serializable AWT component PJ1.1

This class represents a GUI push button that displays a specified textual label. Use setActionCommand() to specify an identifying string that is included in the ActionEvent events generated by the button.

Hierarchy: Object-->Component(java.awt.image.ImageObserver,MenuContainer,Serializable)-->Button

Passed To: Toolkit.createButton()

Canvas	Java 1.0
java.awt	serializable AWT component PJ1.1

A Component that does no default drawing or event handling on its own. You can subclass it to display any kind of drawing or image and handle any kind of user input event. Canvas inherits the event-handling methods of its superclass. In Java 1.1, you can also subclass Component directly to create a lightweight component, instead of having to subclass Canvas.

Hierarchy: Object-->Component(java.awt.image.ImageObserver,MenuContainer,Serializable)-->Canvas

Passed To: Toolkit.createCanvas()

CardLayout	Java 1.0
java.awt	serializable layout manager PJ1.1

A LayoutManager that makes each of the components it manages as large as the container and ensures that only one is visible at a time. The standard LayoutManager methods are called by the Container object and should not be called directly by applet or application code. first(), last(), next(), previous(), and show() make a particular Component in the Container visible. The names with which the components are added to the container are used only by the show() method.

Hierarchy: Object-->CardLayout(LayoutManager2(LayoutManager),Serializable)

Checkbox	Java 1.0
java.awt	serializable AWT component PJ1.1

This class represents a GUI checkbox with a textual label. The Checkbox maintains a boolean state--whether it is checked or not. The checkbox may optionally be part of a CheckboxGroup that enforces radio button behavior.

Hierarchy: Object-->Component(java.awt.image.ImageObserver,MenuContainer,Serializable)-->Checkbox(ItemSelectable)

Passed To: CheckboxGroup.{setCurrent(), setSelectedCheckbox()}, Toolkit.createCheckbox()

Returned By: CheckboxGroup.{getCurrent(), getSelectedCheckbox()}

CheckboxGroup	Java 1.0
java.awt	serializable PJ1.1

A CheckboxGroup object enforces mutual exclusion (also known as radio button behavior) among any number of Checkbox buttons. A Checkbox component can specify a CheckboxGroup object when created or with its setCheckboxGroup() method. If a Checkbox within a CheckboxGroup object is selected, the CheckboxGroup ensures that the previously selected Checkbox becomes unselected.

Hierarchy: Object-->CheckboxGroup(Serializable)

Passed To: Checkbox.{Checkbox(), setCheckboxGroup()}, java.awt.peer.CheckboxPeer.setCheckboxGroup()

Returned By: Checkbox.getCheckboxGroup()

CheckboxMenuItem	Java 1.0
java.awt	serializable AWT component PJ1.1(opt)

This class represents a checkbox with a textual label in a GUI menu. It maintains a boolean state--whether it is checked or not. See also MenuItem.

Hierarchy: Object-->MenuComponent(Serializable)-->MenuItem-->CheckboxMenuItem(ItemSelectable)

Passed To: Toolkit.createCheckboxMenuItem()

Choice	Java 1.0
java.awt	serializable AWT component PJ1.1

This class represents an option menu or dropdown list. The addItem() method adds an item with the specified label to a Choice menu. getSelectedIndex() returns the numerical position of the selected item in the menu, while getSelectedItem() returns the label of the selected item.

Hierarchy: Object-->Component(java.awt.image.ImageObserver,MenuContainer,Serializable)-->Choice(ItemSelectable)

Passed To: Toolkit.createChoice()

Color	Java 1.0
java.awt	serializable PJ1.1

This class describes a color in terms of the individual components of that color. These components are either float values that range between 0 and 1 or 8-bit integers that range from 0 to 255. Prior to Java 1.2, only the RGB (red, green, blue) color space was supported. With the advent of Java 2D, the Color class has been extended to support alpha transparency and arbitrary java.awt.color.ColorSpace objects. In addition, the Java 1.2 Color class implements the Paint interface and is used to perform Java 2D drawing and filling operations that use solid colors.

Color objects can be obtained in a number of ways. The Color() constructors allow color components to be directly specified. The class also defines several color constants. The SystemColor subclass defines other useful Color constants that are related to standard colors used on the system desktop. The static methods HSBtoRGB() and RGBtoHSB() convert between the RGB color space and the HSB (hue, saturation, brightness) color space and can be used to create colors specified using the more intuitive HSB color components. brighter() and darker() return variants on the current color and are useful for creating shading effects.

An RGB color can be expressed as a 24-bit number, where the top 8 bits specifies the red component, the middle 8 bits specifies the green component, and the low 8 bits specifies the blue component. Colors are often represented using a string representation of this 24-bit number. It is particularly common to use a hexadecimal representation for a color, since it keeps the red, green, and blue components distinct. For example, the string "0xFF0000" represents a bright red color: the red component has a value of 255, and both the green and blue components are 0. The static decode() method converts color strings encoded in this way to Color objects. Each getColor() method looks up the specified key in the system properties list and then decodes the value and returns the resulting Color or the specified default color, if no color is found in the properties list.

getRGB() returns the red, green, and blue components of a color as a 24-bit number. getRed(), getBlue(), getGreen(), and getAlpha() return the individual components of a color as integers. getComponents() is a generalized method that returns the color and transparency components of a color in a float array, using an optionally specified ColorSpace. getColorComponents() is similar but returns only the color components, not the transparency component. getRGBComponents() returns the color and alpha components as float values using the RGB color space. getRGBColorComponents() does the same but does not return the alpha component. Each of these methods either fills in the elements of a float[] array you provide or allocates one of its own, if you pass null.

Hierarchy: Object-->Color(Paint(Transparency),Serializable)

Subclasses: SystemColor, javax.swing.plaf.ColorUIResource

Passed To: Too many methods to list.

Returned By: Too many methods to list.

Type Of: Too many fields to list.

Component	Java 1.0
java.awt	serializable AWT component PJ1.1(mod)

Component is the superclass of all GUI components (except menu components) in the java.awt package. You cannot instantiate a Component directly; you must use a subclass.

Component defines many methods. Some of these are intended to be implemented by subclasses, including some that are for handling events. Other methods are used internally by the AWT. And many are useful utility methods for working with GUI components. getParent() returns the Container that contains a Component. setBackground(), setForeground(), and setFont() set the specified display attributes of a component. hide(), show(), enable(), and disable() perform the specified actions for a component. createImage() creates either an Image object from a specified ImageProducer or an off-screen image that can be drawn into and used for double-buffering during animation. Component also has quite a few deprecated methods, as a result of the Java 1.1 event model and the introduction of the JavaBeans method-naming conventions. The class defines numerous methods for handling many types of events, using the 1.0 and 1.1 event models, in both their high-level and low-level forms.

In Personal Java environments, the setCursor() method can be ignored. Also, the Personal Java API supports the isDoubleBuffered() method, even though it is not part of the Java 1.1 API from which Personal Java is derived.

Hierarchy: Object-->Component(java.awt.image.ImageObserver,MenuContainer,Serializable)

Subclasses: Button, Canvas, Checkbox, Choice, Container, Label, java.awt.List, Scrollbar, TextComponent, javax.swing.Box.Filler

Passed To: Too many methods to list.

Returned By: Too many methods to list.

Type Of: Too many fields to list.

ComponentOrientation	Java 1.2
java.awt	serializable

This class encapsulates differences in the way characters in GUI components are arranged into lines and the way lines are grouped into blocks. In western languages like English, characters are arranged left to right and lines are arranged top to bottom, but this is not true throughout the world. In Hebrew, for example, characters are arranged from right to left, and in traditional Chinese, characters are arranged from top to bottom.

The isHorizontal() and isLeftToRight() methods specify the necessary orientation information. The class defines two constants for commonly used orientation types. Authors of AWT, Swing, and JavaBeans components may want to take orientation into account when developing their components (see the getComponentOrientation() method of Component). Applications that use these components should typically not have to worry about this class.

You can query the default orientation for a given java.util.Locale by calling the static getOrientation() method. Set the componentOrientation property of all components in a window by passing a ResourceBundle object to the applyResourceBundle() method of a Window. This looks up the "Orientation" resource in the bundle and, if it is not found, uses the default orientation for the locale of the bundle.

Hierarchy: Object-->ComponentOrientation(Serializable)

Passed To: Component.setComponentOrientation()

Returned By: Component.getComponentOrientation(), ComponentOrientation.getOrientation()

Type Of: ComponentOrientation.{LEFT_TO_RIGHT, RIGHT_TO_LEFT, UNKNOWN}

Composite	Java 1.2
java.awt

This interface defines how two colors are combined to yield a composite color. When Java 2D performs a drawing operation, it uses a Composite object to combine the colors it wants to draw with the colors that already exist on the screen or in the off-screen image.

The default compositing operation is to draw the new color on top of the color already on the screen. If the new color is fully opaque, the existing color is ignored. If the new color is partially transparent, however, it is combined with the color already on the screen to produce a composite color. To specify a different compositing operation, pass a Composite object to the setComposite() method of a Graphics2D object.

AlphaComposite is a commonly used implementation of Composite; it combines colors in a number of possible ways based on their alpha-transparency levels. AlphaComposite is suitable for most uses; very few applications should have to define a custom implementation of Composite.

Note that the only method of Composite, createContext(), does not perform compositing itself. Instead, it returns a CompositeContext object suitable for compositing colors encoded using the specified color models and rendering hints. It is the CompositeContext object that performs the actual work of combining colors.

Implementations: AlphaComposite

Passed To: Graphics2D.setComposite()

Returned By: Graphics2D.getComposite()

CompositeContext	Java 1.2
java.awt

This interface defines the methods that do the actual work of compositing colors. The CompositeContext interface is used internally by Java 2D; applications never need to call CompositeContext methods. And only applications that implement a custom Composite class need to implement this interface.

A CompositeContext object holds the state for a particular compositing operation (in multi-threaded programs, there may be several compositing operations in progress at once). A Graphics2D object creates CompositeContext objects as needed by calling the createContext() method of its Composite object.

Once a CompositeContext object has been created, its compose() method is responsible for combining the colors of the first two Raster objects passed to it and storing the resulting colors in the specified WriteableRaster. (This WriteableRaster is usually the same object as one of the first two arguments.) The dispose() method should free any resources held by the CompositeContext. It is called when the Graphics2D no longer requires the CompositeContext.

Returned By: AlphaComposite.createContext(), Composite.createContext()

Container	Java 1.0
java.awt	serializable AWT component PJ1.1

This class implements a component that can contain other components. You cannot instantiate Container directly but must use one of its subclasses, such as Panel, Frame, or Dialog. Once a Container is created, you can set its LayoutManager with setLayout(), add components to it with add(), and remove them with remove(). getComponents() returns an array of the components contained in a Container. locate() determines within which contained component a specified point falls. list() produces helpful debugging output.

Hierarchy: Object-->Component(java.awt.image.ImageObserver,MenuContainer,Serializable)-->Container

Subclasses: Panel, ScrollPane, Window, javax.swing.Box, javax.swing.CellRendererPane, javax.swing.JComponent, javax.swing.tree.DefaultTreeCellEditor.EditorContainer

Passed To: Too many methods to list.

Returned By: Too many methods to list.

Type Of: javax.swing.JRootPane.contentPane, javax.swing.tree.DefaultTreeCellEditor.editingContainer

Cursor	Java 1.1
java.awt	serializable PJ1.1

This class represents a mouse cursor. It defines a number of constants, which represent the 14 predefined cursors provided by Java 1.0 and Java 1.1. You can pass one of these constants to the constructor to create a cursor of the specified type. Call getType() to determine the type of an existing Cursor object. Since there are only a fixed number of available cursors, the static method getPredefinedCursor() is more efficient than the Cursor() constructor--it maintains a cache of Cursor objects that can be reused. The static getDefaultCursor() method returns the default cursor for the underlying system.

In Java 1.2, the Cursor class has a new getSystemCustomCursor() method that returns a named cursor defined by a system administrator in a systemwide cursors.properties file. Since there is no way to query the list of system-specific custom cursors, however, this method is rarely used. Instead, you can create your own custom cursor by calling the createCustomCursor() method of the Toolkit object. You should first check whether custom cursors are supported by calling the getBestCursorSize() method of Toolkit. If this method indicates a width or height of 0, custom cursors are not supported (by either the Java implementation or the underlying windowing system).

Hierarchy: Object-->Cursor(Serializable)

Passed To: Too many methods to list.

Returned By: Too many methods to list.

Type Of: Cursor.predefined, java.awt.dnd.DragSource.{DefaultCopyDrop, DefaultCopyNoDrop, DefaultLinkDrop, DefaultLinkNoDrop, DefaultMoveDrop, DefaultMoveNoDrop}

Dialog	Java 1.0
java.awt	serializable AWT component PJ1.1(mod)

This class represents a dialog box window. A Dialog can be modal, so that it blocks user input to all other windows until dismissed. It is optional whether a dialog has a title and whether it is resizable. A Dialog object is a Container, so you can add Component objects to it in the normal way with the add() method. The default LayoutManager for Dialog is BorderLayout. You can specify a different LayoutManager object with setLayout(). Call the pack() method of Window to initiate layout management of the dialog and set its initial size appropriately. Call show() to pop a dialog up and setVisible(false) to pop it down. For modal dialogs, show() blocks until the dialog is dismissed. Event handling continues while show() is blocked, using a new event dispatcher thread. In Java 1.0, show() is inherited from Window. Call the Window.dispose() method when the Dialog is no longer needed so that its window system resources may be reused.

In Personal Java environments, support for modeless dialogs is optional, and the Dialog() constructors can throw an exception if you attempt to create a modeless dialog. Also, the setResizable() method is optional, and calls to it can be ignored.

Hierarchy: Object-->Component(java.awt.image.ImageObserver,MenuContainer,Serializable)-->Container-->Window-->Dialog

Subclasses: FileDialog, javax.swing.JDialog

Passed To: Dialog.Dialog(), Toolkit.createDialog(), javax.swing.JDialog.JDialog()

Dimension	Java 1.0
java.awt	cloneable serializable PJ1.1

This class contains two integer fields that describe a width and a height of something. The fields are public and can be manipulated directly.

In Java 1.0 and Java 1.1, Dimension is a subclass of Object. In Java 1.2, with the introduction of Java 2D, it has become a concrete subclass of java.awt.geom.Dimension2D. Contrast Dimension with Dimension2D,which represents the width and height with double values.

Hierarchy: Object-->java.awt.geom.Dimension2D(Cloneable)-->Dimension(Serializable)

Subclasses: javax.swing.plaf.DimensionUIResource

Passed To: Too many methods to list.

Returned By: Too many methods to list.

Type Of: javax.swing.JTable.preferredViewportSize

Event	Java 1.0
java.awt	serializable PJ1.1

This class contains public instance variables that describe some kind of GUI event. In Java 1.1, this class has been superseded by AWTEvent and the java.awt.event package.

The class contains a large number of constants. Some of the constants specify the event type and are values for the id variable. Other constants are values for keys, such as the function keys, that do not have ASCII (Latin-1) values and are set on the key field. Other constants are mask values that are ORed into the modifiers field to describe the state of the modifier keys on the keyboard. The target field is very important--it is the object for which the event occurred. The when field specifies when the event occurred. The x and y fields specify the mouse coordinates at which it occurred. Finally, the arg field is a value specific to the type of the event. Not all fields have valid values for all types of events.

Hierarchy: Object-->Event(Serializable)

Passed To: Too many methods to list.

Type Of: Event.evt

EventQueue	Java 1.1
java.awt	PJ1.1

This class implements an event queue for AWT events in Java 1.1. When an EventQueue is created, a new thread is automatically created and started to remove events from the front of the queue and dispatch them to the appropriate component. It is this thread, created by the EventQueue, that notifies event listeners and executes most of the code in a typical GUI-driven application.

An application can create and use its own private EventQueue, but all AWT events are placed on and dispatched from a single system EventQueue. Use the getSystemEventQueue() method of the Toolkit class to get the system EventQueue object.

getNextEvent() removes and returns the event at the front of the queue. It blocks if there are no events in the queue. peekEvent() returns the event at the front of the queue without removing it from the queue. Passed an optional AWTEventid field, it returns the first event of the specified type. Finally, postEvent() places a new event on the end of the event queue.

In Java 1.2, EventQueue defines three useful static methods. isDispatchThread() returns true if the calling thread is the AWT event dispatch thread. To avoid thread-safety issues, all modifications to AWT and Swing components should be done from this dispatch thread. If another thread needs to operate on a component, it should wrap the desired operation in a Runnable object and pass that object to invokeLater() or invokeAndWait(). These methods bundle the Runnable object into an ActiveEvent that is placed on the queue. When the ActiveEvent reaches the head of the queue, the Runnable code is invoked by the event dispatch thread and can safely modify any AWT and Swing components. invokeLater() returns immediately, while invokeAndWait() blocks until the Runnable code has been run. It is an error to call invokeAndWait() from the event dispatch thread itself. See also ActiveEvent and javax.swing.SwingUtilities. Except for these useful static methods, most applications do not need to use the EventQueue class at all; they can simply rely on the system to dispatch events automatically.

Passed To: EventQueue.push()

Returned By: Toolkit.{getSystemEventQueue(), getSystemEventQueueImpl()}

FileDialog	Java 1.0
java.awt	serializable AWT component PJ1.1(opt)

This class represents a file selection dialog box. The constants LOAD and SAVE are values of an optional constructor argument that specifies whether the dialog should be an Open File dialog or a Save As dialog. You may specify a FilenameFilter object to control the files that are displayed in the dialog.

The inherited show() method pops the dialog up. For dialogs of this type, show() blocks, not returning until the user has selected a file and dismissed the dialog (which pops down automatically--you don't have to call hide()). Once show() has returned, use getFile() to get the name of the file the user selected.

Hierarchy: Object-->Component(java.awt.image.ImageObserver,MenuContainer,Serializable)-->Container-->Window-->Dialog-->FileDialog

Passed To: Toolkit.createFileDialog()