Java tutorial
/* * Copyright (c) 1997, 2014, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package javax.swing.plaf; import javax.swing.JComponent; import javax.swing.SwingUtilities; import javax.accessibility.Accessible; import java.awt.Component; 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 appropriately 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 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 appropriately 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 is time to paint the specified * component. This method is invoked by <code>JComponent</code> * when the specified component is being painted. * * <p>By default this method fills the specified component with * its background color if its {@code opaque} property is {@code true}, * and then immediately calls {@code paint}. In general this method need * not be overridden by subclasses; all look-and-feel rendering code should * reside in the {@code paint} 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 * @return a {@code Dimension} object containing given component's preferred * size appropriate for the look and feel * @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 * @return {@code true} if the specified {@code x,y} location is contained * within the look and feel's defined shape for the given component * @see javax.swing.JComponent#contains * @see java.awt.Component#contains */ @SuppressWarnings("deprecation") 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. * * @param c a {@code JComponent} for which to create a UI delegate * @return a {@code ComponentUI} object for {@code c} */ public static ComponentUI createUI(JComponent c) { throw new Error("ComponentUI.createUI not implemented."); } /** * Returns the baseline. The baseline is measured from the top of * the component. This method is primarily meant for * <code>LayoutManager</code>s to align components along their * baseline. A return value less than 0 indicates this component * does not have a reasonable baseline and that * <code>LayoutManager</code>s should not align this component on * its baseline. * <p> * This method returns -1. Subclasses that have a meaningful baseline * should override appropriately. * * @param c <code>JComponent</code> baseline is being requested for * @param width the width to get the baseline for * @param height the height to get the baseline for * @throws NullPointerException if <code>c</code> is <code>null</code> * @throws IllegalArgumentException if width or height is < 0 * @return baseline or a value < 0 indicating there is no reasonable * baseline * @see javax.swing.JComponent#getBaseline(int,int) * @since 1.6 */ public int getBaseline(JComponent c, int width, int height) { if (c == null) { throw new NullPointerException("Component must be non-null"); } if (width < 0 || height < 0) { throw new IllegalArgumentException("Width and height must be >= 0"); } return -1; } /** * Returns an enum indicating how the baseline of the component * changes as the size changes. This method is primarily meant for * layout managers and GUI builders. * <p> * This method returns <code>BaselineResizeBehavior.OTHER</code>. * Subclasses that support a baseline should override appropriately. * * @param c <code>JComponent</code> to return baseline resize behavior for * @return an enum indicating how the baseline changes as the component * size changes * @throws NullPointerException if <code>c</code> is <code>null</code> * @see javax.swing.JComponent#getBaseline(int, int) * @since 1.6 */ public Component.BaselineResizeBehavior getBaselineResizeBehavior(JComponent c) { if (c == null) { throw new NullPointerException("Component must be non-null"); } return Component.BaselineResizeBehavior.OTHER; } /** * 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. * * @param c {@code JComponent} for which to get count of accessible children * @return the number of accessible children in the object * @see #getAccessibleChild */ 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. * * @param c a {@code JComponent} for which to get a child object * @param i zero-based index of child * @return the <code>i</code>th <code>Accessible</code> child of the object * @see #getAccessibleChildrenCount */ public Accessible getAccessibleChild(JComponent c, int i) { return SwingUtilities.getAccessibleChild(c, i); } }