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ComponentUI.javaAPI DocJava SE 5 API11937Fri Aug 26 14:58:02 BST 2005javax.swing.plaf

ComponentUI.java

/*
 * @(#)ComponentUI.java	1.24 03/12/19
 *
 * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package javax.swing.plaf;

import javax.swing.JComponent;
import javax.swing.SwingUtilities;
import javax.accessibility.Accessible;

import java.awt.Container;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Insets;


/**
 * The base class for all UI delegate objects in the Swing pluggable
 * look and feel architecture.  The UI delegate object for a Swing
 * component is responsible for implementing the aspects of the
 * component that depend on the look and feel.
 * The <code>JComponent</code> class 
 * invokes methods from this class in order to delegate operations
 * (painting, layout calculations, etc.) that may vary depending on the
 * look and feel installed.  <b>Client programs should not invoke methods
 * on this class directly.</b>
 * 
 * @see javax.swing.JComponent
 * @see javax.swing.UIManager 
 * 
 */
public abstract class ComponentUI {
    /**
     * Sole constructor. (For invocation by subclass constructors,
     * typically implicit.)
     */
    public ComponentUI() {
    }

    /**
     * Configures the specified component appropriate for the look and feel.
     * This method is invoked when the <code>ComponentUI</code> instance is being installed
     * as the UI delegate on the specified component.  This method should
     * completely configure the component for the look and feel,
     * including the following:
     * <ol>
     * <li>Install any default property values for color, fonts, borders,
     *     icons, opacity, etc. on the component.  Whenever possible, 
     *     property values initialized by the client program should <i>not</i> 
     *     be overridden.
     * <li>Install a <code>LayoutManager</code> on the component if necessary.
     * <li>Create/add any required sub-components to the component.
     * <li>Create/install event listeners on the component.
     * <li>Create/install a <code>PropertyChangeListener</code> on the component in order
     *     to detect and respond to component property changes appropriately.
     * <li>Install keyboard UI (mnemonics, traversal, etc.) on the component.
     * <li>Initialize any appropriate instance data.
     * </ol>
     * @param c the component where this UI delegate is being installed
     *
     * @see #uninstallUI
     * @see javax.swing.JComponent#setUI
     * @see javax.swing.JComponent#updateUI
     */
    public void installUI(JComponent c) {
    }

    /**
     * Reverses configuration which was done on the specified component during
     * <code>installUI</code>.  This method is invoked when this 
     * <code>UIComponent</code> instance is being removed as the UI delegate 
     * for the specified component.  This method should undo the
     * configuration performed in <code>installUI</code>, being careful to 
     * leave the <code>JComponent</code> instance in a clean state (no 
     * extraneous listeners, look-and-feel-specific property objects, etc.).
     * This should include the following:
     * <ol>
     * <li>Remove any UI-set borders from the component.
     * <li>Remove any UI-set layout managers on the component.
     * <li>Remove any UI-added sub-components from the component.
     * <li>Remove any UI-added event/property listeners from the component.
     * <li>Remove any UI-installed keyboard UI from the component.
     * <li>Nullify any allocated instance data objects to allow for GC.
     * </ol>
     * @param c the component from which this UI delegate is being removed;
     *          this argument is often ignored,
     *          but might be used if the UI object is stateless
     *          and shared by multiple components
     *
     * @see #installUI
     * @see javax.swing.JComponent#updateUI
     */
    public void uninstallUI(JComponent c) {
    }

    /**
     * Paints the specified component appropriate for the look and feel.
     * This method is invoked from the <code>ComponentUI.update</code> method when 
     * the specified component is being painted.  Subclasses should override 
     * this method and use the specified <code>Graphics</code> object to 
     * render the content of the component.
     *
     * @param g the <code>Graphics</code> context in which to paint
     * @param c the component being painted;
     *          this argument is often ignored,
     *          but might be used if the UI object is stateless
     *          and shared by multiple components
     *
     * @see #update
     */ 
    public void paint(Graphics g, JComponent c) {
    }

    /**
     * Notifies this UI delegate that it's time to paint the specified
     * component.  This method is invoked by <code>JComponent</code> 
     * when the specified component is being painted. 
     * By default this method will fill the specified component with
     * its background color (if its <code>opaque</code> property is
     * <code>true</code>) and then immediately call <code>paint</code>.
     * In general this method need not be overridden by subclasses;
     * all look-and-feel rendering code should reside in the <code>paint</code>
     * method.
     *
     * @param g the <code>Graphics</code> context in which to paint
     * @param c the component being painted;
     *          this argument is often ignored,
     *          but might be used if the UI object is stateless
     *          and shared by multiple components
     * 
     * @see #paint
     * @see javax.swing.JComponent#paintComponent
     */ 
    public void update(Graphics g, JComponent c) {
	if (c.isOpaque()) {
	    g.setColor(c.getBackground());
	    g.fillRect(0, 0, c.getWidth(),c.getHeight());
	}
	paint(g, c);
    }

    /**
     * Returns the specified component's preferred size appropriate for
     * the look and feel.  If <code>null</code> is returned, the preferred
     * size will be calculated by the component's layout manager instead 
     * (this is the preferred approach for any component with a specific
     * layout manager installed).  The default implementation of this 
     * method returns <code>null</code>.
     *
     * @param c the component whose preferred size is being queried;
     *          this argument is often ignored,
     *          but might be used if the UI object is stateless
     *          and shared by multiple components
     *
     * @see javax.swing.JComponent#getPreferredSize
     * @see java.awt.LayoutManager#preferredLayoutSize
     */
    public Dimension getPreferredSize(JComponent c) {
	return null;
    }

    /**
     * Returns the specified component's minimum size appropriate for
     * the look and feel.  If <code>null</code> is returned, the minimum
     * size will be calculated by the component's layout manager instead 
     * (this is the preferred approach for any component with a specific
     * layout manager installed).  The default implementation of this 
     * method invokes <code>getPreferredSize</code> and returns that value.
     *
     * @param c the component whose minimum size is being queried;
     *          this argument is often ignored,
     *          but might be used if the UI object is stateless
     *          and shared by multiple components
     *
     * @return a <code>Dimension</code> object or <code>null</code>
     *
     * @see javax.swing.JComponent#getMinimumSize
     * @see java.awt.LayoutManager#minimumLayoutSize
     * @see #getPreferredSize
     */
    public Dimension getMinimumSize(JComponent c) {
	return getPreferredSize(c);
    }

    /**
     * Returns the specified component's maximum size appropriate for
     * the look and feel.  If <code>null</code> is returned, the maximum
     * size will be calculated by the component's layout manager instead 
     * (this is the preferred approach for any component with a specific
     * layout manager installed).  The default implementation of this 
     * method invokes <code>getPreferredSize</code> and returns that value.
     *
     * @param c the component whose maximum size is being queried;
     *          this argument is often ignored,
     *          but might be used if the UI object is stateless
     *          and shared by multiple components
     * @return a <code>Dimension</code> object or <code>null</code>
     *
     * @see javax.swing.JComponent#getMaximumSize
     * @see java.awt.LayoutManager2#maximumLayoutSize
     */
    public Dimension getMaximumSize(JComponent c) {
	return getPreferredSize(c);
    }

    /**
     * Returns <code>true</code> if the specified <i>x,y</i> location is
     * contained within the look and feel's defined shape of the specified 
     * component. <code>x</code> and <code>y</code> are defined to be relative
     * to the coordinate system of the specified component.  Although
     * a component's <code>bounds</code> is constrained to a rectangle,
     * this method provides the means for defining a non-rectangular
     * shape within those bounds for the purpose of hit detection.
     *
     * @param c the component where the <i>x,y</i> location is being queried;
     *          this argument is often ignored,
     *          but might be used if the UI object is stateless
     *          and shared by multiple components
     * @param x the <i>x</i> coordinate of the point
     * @param y the <i>y</i> coordinate of the point
     *
     * @see javax.swing.JComponent#contains
     * @see java.awt.Component#contains
     */
    public boolean contains(JComponent c, int x, int y) {
	return c.inside(x, y);
    }

    /**
     * Returns an instance of the UI delegate for the specified component.
     * Each subclass must provide its own static <code>createUI</code>
     * method that returns an instance of that UI delegate subclass.
     * If the UI delegate subclass is stateless, it may return an instance
     * that is shared by multiple components.  If the UI delegate is
     * stateful, then it should return a new instance per component.
     * The default implementation of this method throws an error, as it
     * should never be invoked.
     */
    public static ComponentUI createUI(JComponent c) {
	throw new Error("ComponentUI.createUI not implemented.");
    }

    /**
     * Returns the number of accessible children in the object.  If all
     * of the children of this object implement <code>Accessible</code>,
     * this
     * method should return the number of children of this object.
     * UIs might wish to override this if they present areas on the
     * screen that can be viewed as components, but actual components
     * are not used for presenting those areas.
     *
     * Note: As of v1.3, it is recommended that developers call
     * <code>Component.AccessibleAWTComponent.getAccessibleChildrenCount()</code> instead
     * of this method.
     *
     * @see #getAccessibleChild
     * @return the number of accessible children in the object
     */
    public int getAccessibleChildrenCount(JComponent c) {
        return SwingUtilities.getAccessibleChildrenCount(c);
    }

    /**
     * Returns the <code>i</code>th <code>Accessible</code> child of the object.
     * UIs might need to override this if they present areas on the
     * screen that can be viewed as components, but actual components
     * are not used for presenting those areas.
     *
     * <p>
     *
     * Note: As of v1.3, it is recommended that developers call
     * <code>Component.AccessibleAWTComponent.getAccessibleChild()</code> instead of
     * this method.
     *
     * @see #getAccessibleChildrenCount
     * @param i zero-based index of child
     * @return the <code>i</code>th <code>Accessible</code> child of the object
     */
    public Accessible getAccessibleChild(JComponent c, int i) {
        return SwingUtilities.getAccessibleChild(c, i);
    }
}