JDK8/Java8源码在线阅读

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 * 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).
 *
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 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
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package java.awt.image;

import java.awt.Image;


/**
 * An asynchronous update interface for receiving notifications about
 * Image information as the Image is constructed.
 *
 * @author      Jim Graham
 */
public interface ImageObserver {
    /**
     * This method is called when information about an image which was
     * previously requested using an asynchronous interface becomes
     * available.  Asynchronous interfaces are method calls such as
     * getWidth(ImageObserver) and drawImage(img, x, y, ImageObserver)
     * which take an ImageObserver object as an argument.  Those methods
     * register the caller as interested either in information about
     * the overall image itself (in the case of getWidth(ImageObserver))
     * or about an output version of an image (in the case of the
     * drawImage(img, x, y, [w, h,] ImageObserver) call).
     *
     * <p>This method
     * should return true if further updates are needed or false if the
     * required information has been acquired.  The image which was being
     * tracked is passed in using the img argument.  Various constants
     * are combined to form the infoflags argument which indicates what
     * information about the image is now available.  The interpretation
     * of the x, y, width, and height arguments depends on the contents
     * of the infoflags argument.
     * <p>
     * The <code>infoflags</code> argument should be the bitwise inclusive
     * <b>OR</b> of the following flags: <code>WIDTH</code>,
     * <code>HEIGHT</code>, <code>PROPERTIES</code>, <code>SOMEBITS</code>,
     * <code>FRAMEBITS</code>, <code>ALLBITS</code>, <code>ERROR</code>,
     * <code>ABORT</code>.
     *
     * @param     img   the image being observed.
     * @param     infoflags   the bitwise inclusive OR of the following
     *               flags:  <code>WIDTH</code>, <code>HEIGHT</code>,
     *               <code>PROPERTIES</code>, <code>SOMEBITS</code>,
     *               <code>FRAMEBITS</code>, <code>ALLBITS</code>,
     *               <code>ERROR</code>, <code>ABORT</code>.
     * @param     x   the <i>x</i> coordinate.
     * @param     y   the <i>y</i> coordinate.
     * @param     width    the width.
     * @param     height   the height.
     * @return    <code>false</code> if the infoflags indicate that the
     *            image is completely loaded; <code>true</code> otherwise.
     *
     * @see #WIDTH
     * @see #HEIGHT
     * @see #PROPERTIES
     * @see #SOMEBITS
     * @see #FRAMEBITS
     * @see #ALLBITS
     * @see #ERROR
     * @see #ABORT
     * @see Image#getWidth
     * @see Image#getHeight
     * @see java.awt.Graphics#drawImage
     */
    public boolean imageUpdate(Image img, int infoflags,
                               int x, int y, int width, int height);

    /**
     * This flag in the infoflags argument to imageUpdate indicates that
     * the width of the base image is now available and can be taken
     * from the width argument to the imageUpdate callback method.
     * @see Image#getWidth
     * @see #imageUpdate
     */
    public static final int WIDTH = 1;

    /**
     * This flag in the infoflags argument to imageUpdate indicates that
     * the height of the base image is now available and can be taken
     * from the height argument to the imageUpdate callback method.
     * @see Image#getHeight
     * @see #imageUpdate
     */
    public static final int HEIGHT = 2;

    /**
     * This flag in the infoflags argument to imageUpdate indicates that
     * the properties of the image are now available.
     * @see Image#getProperty
     * @see #imageUpdate
     */
    public static final int PROPERTIES = 4;

    /**
     * This flag in the infoflags argument to imageUpdate indicates that
     * more pixels needed for drawing a scaled variation of the image
     * are available.  The bounding box of the new pixels can be taken
     * from the x, y, width, and height arguments to the imageUpdate
     * callback method.
     * @see java.awt.Graphics#drawImage
     * @see #imageUpdate
     */
    public static final int SOMEBITS = 8;

    /**
     * This flag in the infoflags argument to imageUpdate indicates that
     * another complete frame of a multi-frame image which was previously
     * drawn is now available to be drawn again.  The x, y, width, and height
     * arguments to the imageUpdate callback method should be ignored.
     * @see java.awt.Graphics#drawImage
     * @see #imageUpdate
     */
    public static final int FRAMEBITS = 16;

    /**
     * This flag in the infoflags argument to imageUpdate indicates that
     * a static image which was previously drawn is now complete and can
     * be drawn again in its final form.  The x, y, width, and height
     * arguments to the imageUpdate callback method should be ignored.
     * @see java.awt.Graphics#drawImage
     * @see #imageUpdate
     */
    public static final int ALLBITS = 32;

    /**
     * This flag in the infoflags argument to imageUpdate indicates that
     * an image which was being tracked asynchronously has encountered
     * an error.  No further information will become available and
     * drawing the image will fail.

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