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java.awt
Class Component

java.lang.Object   
  java.awt.Component

All Implemented Interfaces:: ImageObserver , MenuContainer , Serializable

Direct Known Subclasses:: Button , Canvas , Checkbox , Choice , Container , Label , List , Scrollbar , TextComponent

public abstract class Component
extends Object
implements ImageObserver , MenuContainer , Serializable
extends Object
implements ImageObserver , MenuContainer , Serializable

A component is an object having a graphical representation that can be displayed on the screen and that can interact with the user. Examples of components are the buttons, checkboxes, and scrollbars of a typical graphical user interface.

The Component class is the abstract superclass of the nonmenu-related Abstract Window Toolkit components. Class Component can also be extended directly to create a lightweight component. A lightweight component is a component that is not associated with a native opaque window.

Serialization

It is important to note that only AWT listeners which conform to the Serializable protocol will be saved when the object is stored. If an AWT object has listeners that aren't marked serializable, they will be dropped at writeObject time. Developers will need, as always, to consider the implications of making an object serializable. One situation to watch out for is this:

    import java.awt.*;
    import java.awt.event.*;
    import java.io.Serializable;
    
    class MyApp implements ActionListener, Serializable
    {
        BigObjectThatShouldNotBeSerializedWithAButton bigOne;
        Button aButton = new Button();
      
        MyApp()
        {
            // Oops, now aButton has a listener with a reference
            // to bigOne!
            aButton.addActionListener(this);
        }
    
        public void actionPerformed(ActionEvent e)
        {
            System.out.println("Hello There");
        }
    }

In this example, serializing aButton by itself will cause MyApp and everything it refers to to be serialized as well. The problem is that the listener is serializable by coincidence, not by design. To separate the decisions about MyApp and the ActionListener being serializable one can use a nested class, as in the following example:

    import java.awt.*;
    import java.awt.event.*;
    import java.io.Serializable;

    class MyApp java.io.Serializable
    {
         BigObjectThatShouldNotBeSerializedWithAButton bigOne;
         Button aButton = new Button();

         class MyActionListener implements ActionListener
         {
             public void actionPerformed(ActionEvent e)
             {
                 System.out.println("Hello There");
             }
         }
 
         MyApp()
         {
             aButton.addActionListener(new MyActionListener());
         }
    }

Note: For more information on the paint mechanisms utilitized by AWT and Swing, including information on how to write the most efficient painting code, see Painting in AWT and Swing.

For details on the focus subsystem, see How to Use the Focus Subsystem, a section in The Java Tutorial, and the Focus Specification for more information.

See Also:: Serialized Form

Nested Class Summary
`protected class`	`Component.AccessibleAWTComponent` Inner class of Component used to provide default support for accessibility.
`protected class`	`Component.BltBufferStrategy` Inner class for blitting offscreen surfaces to a component.
`protected class`	`Component.FlipBufferStrategy` Inner class for flipping buffers on a component.

Field Summary
`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()`.

Fields inherited from interface java.awt.image.ImageObserver
`ABORT , ALLBITS , ERROR , FRAMEBITS , HEIGHT , PROPERTIES , SOMEBITS , WIDTH`

Constructor Summary
`protected`	`Component ()` Constructs a new component.

Method Summary
`boolean`	`action (Event evt, Object what)` Deprecated. As of JDK version 1.1, should register this component as ActionListener on component which fires action events.
`void`	`add (PopupMenu popup)` Adds the specified popup menu to the component.
`void`	`addComponentListener (ComponentListener l)` Adds the specified component listener to receive component events from this component.
`void`	`addFocusListener (FocusListener l)` Adds the specified focus listener to receive focus events from this component when this component gains input focus.
`void`	`addHierarchyBoundsListener (HierarchyBoundsListener l)` Adds the specified hierarchy bounds listener to receive hierarchy bounds events from this component when the hierarchy to which this container belongs changes.
`void`	`addHierarchyListener (HierarchyListener l)` Adds the specified hierarchy listener to receive hierarchy changed events from this component when the hierarchy to which this container belongs changes.
`void`	`addInputMethodListener (InputMethodListener l)` Adds the specified input method listener to receive input method events from this component.
`void`	`addKeyListener (KeyListener l)` Adds the specified key listener to receive key events from this component.
`void`	`addMouseListener (MouseListener l)` Adds the specified mouse listener to receive mouse events from this component.
`void`	`addMouseMotionListener (MouseMotionListener l)` Adds the specified mouse motion listener to receive mouse motion events from this component.
`void`	`addMouseWheelListener (MouseWheelListener l)` Adds the specified mouse wheel listener to receive mouse wheel events from this component.
`void`	`addNotify ()` Makes this `Component` displayable by connecting it to a native screen resource.
`void`	`addPropertyChangeListener (PropertyChangeListener listener)` Adds a PropertyChangeListener to the listener list.
`void`	`addPropertyChangeListener (String propertyName, PropertyChangeListener listener)` Adds a PropertyChangeListener to the listener list for a specific property.
`void`	`applyComponentOrientation (ComponentOrientation orientation)` Sets the `ComponentOrientation` property of this component and all components contained within it.
`boolean`	`areFocusTraversalKeysSet (int id)` Returns whether the Set of focus traversal keys for the given focus traversal operation has been explicitly defined for this Component.
`Rectangle`	`bounds ()` Deprecated. As of JDK version 1.1, replaced by `getBounds()`.
`int`	`checkImage (Image image, ImageObserver observer)` Returns the status of the construction of a screen representation of the specified image.
`int`	`checkImage (Image image, int width, int height, ImageObserver observer)` Returns the status of the construction of a screen representation of the specified image.
`protected AWTEvent`	`coalesceEvents (AWTEvent existingEvent, AWTEvent newEvent)` Potentially coalesce an event being posted with an existing event.
`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.
`Image`	`createImage (ImageProducer producer)` Creates an image from the specified image producer.
`Image`	`createImage (int width, int height)` Creates an off-screen drawable image to be used for double buffering.
`VolatileImage`	`createVolatileImage (int width, int height)` Creates a volatile off-screen drawable image to be used for double buffering.
`VolatileImage`	`createVolatileImage (int width, int height, ImageCapabilities caps)` Creates a volatile off-screen drawable image, with the given capabilities.
`void`	`deliverEvent (Event e)` Deprecated. As of JDK version 1.1, replaced by `dispatchEvent(AWTEvent e)`.
`void`	`disable ()` Deprecated. As of JDK version 1.1, replaced by `setEnabled(boolean)`.
`protected void`	`disableEvents (long eventsToDisable)` Disables the events defined by the specified event mask parameter from being delivered to this component.
`void`	`dispatchEvent (AWTEvent e)` Dispatches an event to this component or one of its sub components.
`void`	`doLayout ()` Prompts the layout manager to lay out this component.
`void`	`enable ()` Deprecated. As of JDK version 1.1, replaced by `setEnabled(boolean)`.
`void`	`enable (boolean b)` Deprecated. As of JDK version 1.1, replaced by `setEnabled(boolean)`.
`protected void`	`enableEvents (long eventsToEnable)` Enables the events defined by the specified event mask parameter to be delivered to this component.
`void`	`enableInputMethods (boolean enable)` Enables or disables input method support for this component.
`protected void`	`firePropertyChange (String propertyName, boolean oldValue, boolean newValue)` Support for reporting bound property changes for boolean properties.
`void`	`firePropertyChange (String propertyName, byte oldValue, byte newValue)` Reports a bound property change.
`void`	`firePropertyChange (String propertyName, char oldValue, char newValue)` Reports a bound property change.
`void`	`firePropertyChange (String propertyName, double oldValue, double newValue)` Reports a bound property change.
`void`	`firePropertyChange (String propertyName, float oldValue, float newValue)` Reports a bound property change.
`protected void`	`firePropertyChange (String propertyName, int oldValue, int newValue)` Support for reporting bound property changes for integer properties.
`void`	`firePropertyChange (String propertyName, long oldValue, long newValue)` Reports a bound property change.
`protected void`	`firePropertyChange (String propertyName, Object oldValue, Object newValue)` Support for reporting bound property changes for Object properties.
`void`	`firePropertyChange (String propertyName, short oldValue, short newValue)` Reports a bound property change.
`AccessibleContext`	`getAccessibleContext ()` Gets the `AccessibleContext` associated with 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.
`Rectangle`	`getBounds (Rectangle rv)` Stores the bounds of this component into "return value" rv and return rv.
`ColorModel`	`getColorModel ()` Gets the instance of `ColorModel` used to display the component on the output device.
`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.
`ComponentListener []`	`getComponentListeners ()` Returns an array of all the component listeners registered on this component.
`ComponentOrientation`	`getComponentOrientation ()` Retrieves the language-sensitive orientation that is to be used to order the elements or text within this component.
`Cursor`	`getCursor ()` Gets the cursor set in the component.
`DropTarget`	`getDropTarget ()` Gets the `DropTarget` associated with this `Component`.
`Container`	`getFocusCycleRootAncestor`

java.awt Class Component

Serialization

java.awt
Class Component