1 /*
   2  * Copyright (c) 1995, 2014, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  26 package sun.applet;
  27 
  28 import java.awt.Toolkit;
  29 import java.awt.Image;
  30 import java.lang.ref.SoftReference;
  31 import sun.awt.image.URLImageSource;
  32 import java.net.URL;
  33 
  34 class AppletImageRef {
  35     private SoftReference<Image> soft = null;
  36 
  37     URL url;
  38 
  39     /**
  40      * Returns a pointer to the object referenced by this Ref.  If the object
  41      * has been thrown away by the garbage collector, it will be
  42      * reconstituted. This method does everything necessary to ensure that the garbage
  43      * collector throws things away in Least Recently Used(LRU) order.  Applications should
  44      * never override this method. The get() method effectively caches calls to
  45      * reconstitute().
  46      */
  47     public synchronized Image get() {
  48         Image t = check();
  49         if (t == null) {
  50             t = reconstitute();
  51             setThing(t);
  52         }
  53         return t;
  54     }
  55 
  56     /**
  57      * Create the Ref
  58      */
  59     AppletImageRef(URL url) {
  60         this.url = url;
  61     }
  62 
  63     /**
  64      * Flushes the cached object.  Forces the next invocation of get() to
  65      * invoke reconstitute().
  66      */
  67     public synchronized void flush() {
  68         SoftReference s = soft;
  69         if (s != null) s.clear();
  70         soft = null;
  71     }
  72 
  73     /**
  74      * Sets the thing to the specified object.
  75      * @param thing the specified object
  76      */
  77     public synchronized void setThing(Object thing) {
  78         flush();
  79         soft = new SoftReference(thing);
  80     }
  81 
  82     /**
  83      * Checks to see what object is being pointed at by this Ref and returns it.
  84      */
  85     public synchronized Image check() {
  86         SoftReference<Image> s = soft;
  87         if (s == null) return null;
  88         return s.get();
  89     }
  90 
  91     /**
  92      * Reconsitute the image.  Only called when the ref has been flushed.
  93      */
  94     public Image reconstitute() {
  95         Image img = Toolkit.getDefaultToolkit().createImage(new URLImageSource(url));
  96         return img;
  97     }
  98 }