JDK8/Java8源码在线阅读
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*
* This code is distributed in the hope that it will be useful, but WITHOUT
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* accompanied this code).
*
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*
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package java.awt;
import java.awt.image.BufferedImage;
import java.security.AccessController;
import java.util.Locale;
import sun.font.FontManager;
import sun.font.FontManagerFactory;
import sun.java2d.HeadlessGraphicsEnvironment;
import sun.java2d.SunGraphicsEnvironment;
import sun.security.action.GetPropertyAction;
/**
*
* The <code>GraphicsEnvironment</code> 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</code> might be local
* or on a remote machine. <code>GraphicsDevice</code> objects can be
* screens, printers or image buffers and are the destination of
* {@link Graphics2D} drawing methods. Each <code>GraphicsDevice</code>
* has a number of {@link GraphicsConfiguration} objects associated with
* it. These objects specify the different configurations in which the
* <code>GraphicsDevice</code> can be used.
* @see GraphicsDevice
* @see GraphicsConfiguration
*/
public abstract class GraphicsEnvironment {
private static GraphicsEnvironment localEnv;
/**
* 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() {
}
/**
* Returns the local <code>GraphicsEnvironment</code>.
* @return the local <code>GraphicsEnvironment</code>
*/
public static synchronized GraphicsEnvironment getLocalGraphicsEnvironment() {
if (localEnv == null) {
localEnv = createGE();
}
return localEnv;
}
/**
* Creates and returns the GraphicsEnvironment, according to the
* system property 'java.awt.graphicsenv'.
*
* @return the graphics environment
*/
private static GraphicsEnvironment createGE() {
GraphicsEnvironment ge;
String nm = AccessController.doPrivileged(new GetPropertyAction("java.awt.graphicsenv", null));
try {
// long t0 = System.currentTimeMillis();
Class<GraphicsEnvironment> geCls;
try {
// First we try if the bootclassloader finds the requested
// class. This way we can avoid to run in a privileged block.
geCls = (Class<GraphicsEnvironment>)Class.forName(nm);
} catch (ClassNotFoundException ex) {
// If the bootclassloader fails, we try again with the
// application classloader.
ClassLoader cl = ClassLoader.getSystemClassLoader();
geCls = (Class<GraphicsEnvironment>)Class.forName(nm, true, cl);
}
ge = geCls.newInstance();
// long t1 = System.currentTimeMillis();
// System.out.println("GE creation took " + (t1-t0)+ "ms.");
if (isHeadless()) {
ge = new HeadlessGraphicsEnvironment(ge);
}
} catch (ClassNotFoundException e) {
throw new Error("Could not find class: "+nm);
} catch (InstantiationException e) {
throw new Error("Could not instantiate Graphics Environment: "
+ nm);
} catch (IllegalAccessException e) {
throw new Error ("Could not access Graphics Environment: "
+ nm);
}
return ge;
}
/**
* 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</code> if this environment cannot support
* a display, keyboard, and mouse; <code>false</code>
* 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 :
"\nNo X11 DISPLAY variable was set, " +
"but this program performed an operation which requires it.";
}
/**
* @return the value of the property "java.awt.headless"
* @since 1.4
*/
private static boolean getHeadlessProperty() {
if (headless == null) {
java.security.AccessController.doPrivileged(
new java.security.PrivilegedAction<Object>() {
public Object run() {
String nm = System.getProperty("java.awt.headless");
if (nm == null) {
/* No need to ask for DISPLAY when run in a browser */
if (System.getProperty("javaplugin.version") != null) {
headless = defaultHeadless = Boolean.FALSE;
} else {
String osName = System.getProperty("os.name");
if (osName.contains("OS X") && "sun.awt.HToolkit".equals(
System.getProperty("awt.toolkit")))
{
headless = defaultHeadless = Boolean.TRUE;
} else {
headless = defaultHeadless =
Boolean.valueOf(("Linux".equals(osName) ||
"SunOS".equals(osName) ||
"FreeBSD".equals(osName) ||
"NetBSD".equals(osName) ||
"OpenBSD".equals(osName)) &&
(System.getenv("DISPLAY") == null));
}
}
} else if (nm.equals("true")) {
headless = Boolean.TRUE;
} else {
headless = Boolean.FALSE;
}
return null;
}
}
);
}
return headless.booleanValue();
}
/**
* 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</code> will be thrown from areas of the
* graphics environment that are dependent on a display, keyboard, or
* mouse.
* @return <code>true</code> if a display, keyboard, and mouse
* can be supported in this environment; <code>false</code>
* 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</code>
* objects.
* @return an array containing all the <code>GraphicsDevice</code>
* 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</code>.
* @return the <code>GraphicsDevice</code> that represents the
* default screen device
* @exception HeadlessException if isHeadless() returns true
* @see #isHeadless()
*/
public abstract GraphicsDevice getDefaultScreenDevice()
throws HeadlessException;
/**
* Returns a <code>Graphics2D</code> object for rendering into the
* specified {@link BufferedImage}.
* @param img the specified <code>BufferedImage</code>
* @return a <code>Graphics2D</code> to be used for rendering into
* the specified <code>BufferedImage</code>
* @throws NullPointerException if <code>img</code> 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</code>. 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</code> method on the chosen instance.
* <p>
* This method provides for the application the most precise control
* over which <code>Font</code> instance is used to render text.
* If a font in this <code>GraphicsEnvironment</code> has multiple
* programmable variations, only one
* instance of that <code>Font</code> 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</code> array. The other variations
* must be derived by the application.
*
* @return an array of <code>Font</code> 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</code> localized for the default locale,
* as returned by <code>Locale.getDefault()</code>.
* <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</code> 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</code> 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</code> is equivalent to
* specifying <code>Locale.getDefault()</code>.
* @return an array of <code>String</code> containing font family names
* localized for the specified <code>Locale</code>, 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</code>in this
* <code>GraphicsEnvironment</code>.
* 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</code>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</code> are:
* <ul>
* <li>The font is not a <i>created</i> <code>Font</code>.
* <li>The font conflicts with a non-created <code>Font</code> already
* in this <code>GraphicsEnvironment</code>. 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>
* @return true if the <code>font</code> is successfully
* registered in this <code>GraphicsEnvironment</code>.
* @throws NullPointerException if <code>font</code> 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();
}
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