Java tutorial
/* * Copyright (c) 1997, 2018, 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 java.awt; import java.awt.image.BufferedImage; import java.security.AccessController; import java.security.PrivilegedAction; import java.util.Locale; import sun.awt.PlatformGraphicsInfo; import sun.font.FontManager; import sun.font.FontManagerFactory; import sun.java2d.HeadlessGraphicsEnvironment; import sun.java2d.SunGraphicsEnvironment; import sun.security.action.GetPropertyAction; /** * * The {@code GraphicsEnvironment} class describes the collection * of {@link GraphicsDevice} objects and {@link java.awt.Font} objects * available to a Java(tm) application on a particular platform. * The resources in this {@code GraphicsEnvironment} might be local * or on a remote machine. {@code GraphicsDevice} objects can be * screens, printers or image buffers and are the destination of * {@link Graphics2D} drawing methods. Each {@code GraphicsDevice} * has a number of {@link GraphicsConfiguration} objects associated with * it. These objects specify the different configurations in which the * {@code GraphicsDevice} can be used. * @see GraphicsDevice * @see GraphicsConfiguration */ public abstract class GraphicsEnvironment { /** * The headless state of the Toolkit and GraphicsEnvironment */ private static Boolean headless; /** * The headless state assumed by default */ private static Boolean defaultHeadless; /** * This is an abstract class and cannot be instantiated directly. * Instances must be obtained from a suitable factory or query method. */ protected GraphicsEnvironment() { } /** * Lazy initialization of local graphics environment using holder idiom. */ private static final class LocalGE { /** * The instance of the local {@code GraphicsEnvironment}. */ static final GraphicsEnvironment INSTANCE = createGE(); /** * Creates and returns the GraphicsEnvironment, according to the * platform-specific proxy class. * * @return the graphics environment */ private static GraphicsEnvironment createGE() { GraphicsEnvironment ge = PlatformGraphicsInfo.createGE(); if (isHeadless()) { ge = new HeadlessGraphicsEnvironment(ge); } return ge; } } /** * Returns the local {@code GraphicsEnvironment}. * @return the local {@code GraphicsEnvironment} */ public static GraphicsEnvironment getLocalGraphicsEnvironment() { return LocalGE.INSTANCE; } /** * Tests whether or not a display, keyboard, and mouse can be * supported in this environment. If this method returns true, * a HeadlessException is thrown from areas of the Toolkit * and GraphicsEnvironment that are dependent on a display, * keyboard, or mouse. * @return {@code true} if this environment cannot support * a display, keyboard, and mouse; {@code false} * otherwise * @see java.awt.HeadlessException * @since 1.4 */ public static boolean isHeadless() { return getHeadlessProperty(); } /** * @return warning message if headless state is assumed by default; * null otherwise * @since 1.5 */ static String getHeadlessMessage() { if (headless == null) { getHeadlessProperty(); // initialize the values } return defaultHeadless != Boolean.TRUE ? null : PlatformGraphicsInfo.getDefaultHeadlessMessage(); } /** * @return the value of the property "java.awt.headless" * @since 1.4 */ private static boolean getHeadlessProperty() { if (headless == null) { AccessController.doPrivileged((PrivilegedAction<Void>) () -> { String nm = System.getProperty("java.awt.headless"); if (nm == null) { headless = defaultHeadless = PlatformGraphicsInfo.getDefaultHeadlessProperty(); } else { headless = Boolean.valueOf(nm); } return null; }); } return headless; } /** * Check for headless state and throw HeadlessException if headless * @since 1.4 */ static void checkHeadless() throws HeadlessException { if (isHeadless()) { throw new HeadlessException(); } } /** * Returns whether or not a display, keyboard, and mouse can be * supported in this graphics environment. If this returns true, * {@code HeadlessException} will be thrown from areas of the * graphics environment that are dependent on a display, keyboard, or * mouse. * @return {@code true} if a display, keyboard, and mouse * can be supported in this environment; {@code false} * otherwise * @see java.awt.HeadlessException * @see #isHeadless * @since 1.4 */ public boolean isHeadlessInstance() { // By default (local graphics environment), simply check the // headless property. return getHeadlessProperty(); } /** * Returns an array of all of the screen {@code GraphicsDevice} * objects. * @return an array containing all the {@code GraphicsDevice} * objects that represent screen devices * @exception HeadlessException if isHeadless() returns true * @see #isHeadless() */ public abstract GraphicsDevice[] getScreenDevices() throws HeadlessException; /** * Returns the default screen {@code GraphicsDevice}. * @return the {@code GraphicsDevice} that represents the * default screen device * @exception HeadlessException if isHeadless() returns true * @see #isHeadless() */ public abstract GraphicsDevice getDefaultScreenDevice() throws HeadlessException; /** * Returns a {@code Graphics2D} object for rendering into the * specified {@link BufferedImage}. * @param img the specified {@code BufferedImage} * @return a {@code Graphics2D} to be used for rendering into * the specified {@code BufferedImage} * @throws NullPointerException if {@code img} is null */ public abstract Graphics2D createGraphics(BufferedImage img); /** * Returns an array containing a one-point size instance of all fonts * available in this {@code GraphicsEnvironment}. Typical usage * would be to allow a user to select a particular font. Then, the * application can size the font and set various font attributes by * calling the {@code deriveFont} method on the chosen instance. * <p> * This method provides for the application the most precise control * over which {@code Font} instance is used to render text. * If a font in this {@code GraphicsEnvironment} has multiple * programmable variations, only one * instance of that {@code Font} is returned in the array, and * other variations must be derived by the application. * <p> * If a font in this environment has multiple programmable variations, * such as Multiple-Master fonts, only one instance of that font is * returned in the {@code Font} array. The other variations * must be derived by the application. * * @return an array of {@code Font} objects * @see #getAvailableFontFamilyNames * @see java.awt.Font * @see java.awt.Font#deriveFont * @see java.awt.Font#getFontName * @since 1.2 */ public abstract Font[] getAllFonts(); /** * Returns an array containing the names of all font families in this * {@code GraphicsEnvironment} localized for the default locale, * as returned by {@code Locale.getDefault()}. * <p> * Typical usage would be for presentation to a user for selection of * a particular family name. An application can then specify this name * when creating a font, in conjunction with a style, such as bold or * italic, giving the font system flexibility in choosing its own best * match among multiple fonts in the same font family. * * @return an array of {@code String} containing font family names * localized for the default locale, or a suitable alternative * name if no name exists for this locale. * @see #getAllFonts * @see java.awt.Font * @see java.awt.Font#getFamily * @since 1.2 */ public abstract String[] getAvailableFontFamilyNames(); /** * Returns an array containing the names of all font families in this * {@code GraphicsEnvironment} localized for the specified locale. * <p> * Typical usage would be for presentation to a user for selection of * a particular family name. An application can then specify this name * when creating a font, in conjunction with a style, such as bold or * italic, giving the font system flexibility in choosing its own best * match among multiple fonts in the same font family. * * @param l a {@link Locale} object that represents a * particular geographical, political, or cultural region. * Specifying {@code null} is equivalent to * specifying {@code Locale.getDefault()}. * @return an array of {@code String} containing font family names * localized for the specified {@code Locale}, or a * suitable alternative name if no name exists for the specified locale. * @see #getAllFonts * @see java.awt.Font * @see java.awt.Font#getFamily * @since 1.2 */ public abstract String[] getAvailableFontFamilyNames(Locale l); /** * Registers a <i>created</i> {@code Font} in this * {@code GraphicsEnvironment}. * A created font is one that was returned from calling * {@link Font#createFont}, or derived from a created font by * calling {@link Font#deriveFont}. * After calling this method for such a font, it is available to * be used in constructing new {@code Font}s by name or family name, * and is enumerated by {@link #getAvailableFontFamilyNames} and * {@link #getAllFonts} within the execution context of this * application or applet. This means applets cannot register fonts in * a way that they are visible to other applets. * <p> * Reasons that this method might not register the font and therefore * return {@code false} are: * <ul> * <li>The font is not a <i>created</i> {@code Font}. * <li>The font conflicts with a non-created {@code Font} already * in this {@code GraphicsEnvironment}. For example if the name * is that of a system font, or a logical font as described in the * documentation of the {@link Font} class. It is implementation dependent * whether a font may also conflict if it has the same family name * as a system font. * <p>Notice that an application can supersede the registration * of an earlier created font with a new one. * </ul> * * @param font the font to be registered * @return true if the {@code font} is successfully * registered in this {@code GraphicsEnvironment}. * @throws NullPointerException if {@code font} is null * @since 1.6 */ public boolean registerFont(Font font) { if (font == null) { throw new NullPointerException("font cannot be null."); } FontManager fm = FontManagerFactory.getInstance(); return fm.registerFont(font); } /** * Indicates a preference for locale-specific fonts in the mapping of * logical fonts to physical fonts. Calling this method indicates that font * rendering should primarily use fonts specific to the primary writing * system (the one indicated by the default encoding and the initial * default locale). For example, if the primary writing system is * Japanese, then characters should be rendered using a Japanese font * if possible, and other fonts should only be used for characters for * which the Japanese font doesn't have glyphs. * <p> * The actual change in font rendering behavior resulting from a call * to this method is implementation dependent; it may have no effect at * all, or the requested behavior may already match the default behavior. * The behavior may differ between font rendering in lightweight * and peered components. Since calling this method requests a * different font, clients should expect different metrics, and may need * to recalculate window sizes and layout. Therefore this method should * be called before user interface initialisation. * @since 1.5 */ public void preferLocaleFonts() { FontManager fm = FontManagerFactory.getInstance(); fm.preferLocaleFonts(); } /** * Indicates a preference for proportional over non-proportional (e.g. * dual-spaced CJK fonts) fonts in the mapping of logical fonts to * physical fonts. If the default mapping contains fonts for which * proportional and non-proportional variants exist, then calling * this method indicates the mapping should use a proportional variant. * <p> * The actual change in font rendering behavior resulting from a call to * this method is implementation dependent; it may have no effect at all. * The behavior may differ between font rendering in lightweight and * peered components. Since calling this method requests a * different font, clients should expect different metrics, and may need * to recalculate window sizes and layout. Therefore this method should * be called before user interface initialisation. * @since 1.5 */ public void preferProportionalFonts() { FontManager fm = FontManagerFactory.getInstance(); fm.preferProportionalFonts(); } /** * Returns the Point where Windows should be centered. * It is recommended that centered Windows be checked to ensure they fit * within the available display area using getMaximumWindowBounds(). * @return the point where Windows should be centered * * @exception HeadlessException if isHeadless() returns true * @see #getMaximumWindowBounds * @since 1.4 */ public Point getCenterPoint() throws HeadlessException { // Default implementation: return the center of the usable bounds of the // default screen device. Rectangle usableBounds = SunGraphicsEnvironment.getUsableBounds(getDefaultScreenDevice()); return new Point((usableBounds.width / 2) + usableBounds.x, (usableBounds.height / 2) + usableBounds.y); } /** * Returns the maximum bounds for centered Windows. * These bounds account for objects in the native windowing system such as * task bars and menu bars. The returned bounds will reside on a single * display with one exception: on multi-screen systems where Windows should * be centered across all displays, this method returns the bounds of the * entire display area. * <p> * To get the usable bounds of a single display, use * {@code GraphicsConfiguration.getBounds()} and * {@code Toolkit.getScreenInsets()}. * @return the maximum bounds for centered Windows * * @exception HeadlessException if isHeadless() returns true * @see #getCenterPoint * @see GraphicsConfiguration#getBounds * @see Toolkit#getScreenInsets * @since 1.4 */ public Rectangle getMaximumWindowBounds() throws HeadlessException { // Default implementation: return the usable bounds of the default screen // device. This is correct for Microsoft Windows and non-Xinerama X11. return SunGraphicsEnvironment.getUsableBounds(getDefaultScreenDevice()); } }