JDK8/Java8源码在线阅读

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 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
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package java.awt.image;

import java.awt.Image;
import java.awt.image.ImageFilter;
import java.awt.image.ImageConsumer;
import java.awt.image.ImageProducer;
import java.util.Hashtable;
import java.awt.image.ColorModel;

/**
 * This class is an implementation of the ImageProducer interface which
 * takes an existing image and a filter object and uses them to produce
 * image data for a new filtered version of the original image.
 * Here is an example which filters an image by swapping the red and
 * blue compents:
 * <pre>
 *
 *      Image src = getImage("doc:///demo/images/duke/T1.gif");
 *      ImageFilter colorfilter = new RedBlueSwapFilter();
 *      Image img = createImage(new FilteredImageSource(src.getSource(),
 *                                                      colorfilter));
 *
 * </pre>
 *
 * @see ImageProducer
 *
 * @author      Jim Graham
 */
public class FilteredImageSource implements ImageProducer {
    ImageProducer src;
    ImageFilter filter;

    /**
     * Constructs an ImageProducer object from an existing ImageProducer
     * and a filter object.
     * @param orig the specified <code>ImageProducer</code>
     * @param imgf the specified <code>ImageFilter</code>
     * @see ImageFilter
     * @see java.awt.Component#createImage
     */
    public FilteredImageSource(ImageProducer orig, ImageFilter imgf) {
        src = orig;
        filter = imgf;
    }

    private Hashtable proxies;

    /**
     * Adds the specified <code>ImageConsumer</code>
     * to the list of consumers interested in data for the filtered image.
     * An instance of the original <code>ImageFilter</code>
     * is created
     * (using the filter's <code>getFilterInstance</code> method)
     * to manipulate the image data
     * for the specified <code>ImageConsumer</code>.
     * The newly created filter instance
     * is then passed to the <code>addConsumer</code> method
     * of the original <code>ImageProducer</code>.
     *
     * <p>
     * This method is public as a side effect
     * of this class implementing
     * the <code>ImageProducer</code> interface.
     * It should not be called from user code,
     * and its behavior if called from user code is unspecified.
     *
     * @param ic  the consumer for the filtered image
     * @see ImageConsumer
     */
    public synchronized void addConsumer(ImageConsumer ic) {
        if (proxies == null) {
            proxies = new Hashtable();
        }
        if (!proxies.containsKey(ic)) {
            ImageFilter imgf = filter.getFilterInstance(ic);
            proxies.put(ic, imgf);
            src.addConsumer(imgf);
        }
    }

    /**
     * Determines whether an ImageConsumer is on the list of consumers
     * currently interested in data for this image.
     *
     * <p>
     * This method is public as a side effect
     * of this class implementing
     * the <code>ImageProducer</code> interface.
     * It should not be called from user code,
     * and its behavior if called from user code is unspecified.
     *
     * @param ic the specified <code>ImageConsumer</code>
     * @return true if the ImageConsumer is on the list; false otherwise
     * @see ImageConsumer
     */
    public synchronized boolean isConsumer(ImageConsumer ic) {
        return (proxies != null && proxies.containsKey(ic));
    }

    /**
     * Removes an ImageConsumer from the list of consumers interested in
     * data for this image.
     *
     * <p>
     * This method is public as a side effect
     * of this class implementing
     * the <code>ImageProducer</code> interface.
     * It should not be called from user code,
     * and its behavior if called from user code is unspecified.
     *
     * @see ImageConsumer
     */
    public synchronized void removeConsumer(ImageConsumer ic) {
        if (proxies != null) {
            ImageFilter imgf = (ImageFilter) proxies.get(ic);
            if (imgf != null) {
                src.removeConsumer(imgf);
                proxies.remove(ic);
                if (proxies.isEmpty()) {
                    proxies = null;
                }
            }
        }
    }

    /**
     * Starts production of the filtered image.
     * If the specified <code>ImageConsumer</code>
     * isn't already a consumer of the filtered image,
     * an instance of the original <code>ImageFilter</code>
     * is created
     * (using the filter's <code>getFilterInstance</code> method)
     * to manipulate the image data
     * for the <code>ImageConsumer</code>.
     * The filter instance for the <code>ImageConsumer</code>
     * is then passed to the <code>startProduction</code> method
     * of the original <code>ImageProducer</code>.
     *
     * <p>
     * This method is public as a side effect
     * of this class implementing
     * the <code>ImageProducer</code> interface.
     * It should not be called from user code,
     * and its behavior if called from user code is unspecified.
     *
     * @param ic  the consumer for the filtered image
     * @see ImageConsumer
     */
    public void startProduction(ImageConsumer ic) {
        if (proxies == null) {
            proxies = new Hashtable();
        }
        ImageFilter imgf = (ImageFilter) proxies.get(ic);
        if (imgf == null) {
            imgf = filter.getFilterInstance(ic);
            proxies.put(ic, imgf);
        }
        src.startProduction(imgf);
    }

    /**
     * Requests that a given ImageConsumer have the image data delivered

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