cvs commit: jakarta-ant/src/main/org/apache/tools/ant/util WeakishReference.java

[st...@apache.org]

stevel      2002/09/10 15:19:28

  Added:       src/main/org/apache/tools/ant/util WeakishReference.java
  Log:
  a reference that is hard on 1.1, weak on 1.2+
  
  Revision  Changes    Path
  1.1                  jakarta-ant/src/main/org/apache/tools/ant/util/WeakishReference.java
  
  Index: WeakishReference.java
  ===================================================================
  /*
   *  The Apache Software License, Version 1.1
   *
   *  Copyright (c) 2002 The Apache Software Foundation.  All rights
   *  reserved.
   *
   *  Redistribution and use in source and binary forms, with or without
   *  modification, are permitted provided that the following conditions
   *  are met:
   *
   *  1. Redistributions of source code must retain the above copyright
   *  notice, this list of conditions and the following disclaimer.
   *
   *  2. Redistributions in binary form must reproduce the above copyright
   *  notice, this list of conditions and the following disclaimer in
   *  the documentation and/or other materials provided with the
   *  distribution.
   *
   *  3. The end-user documentation included with the redistribution, if
   *  any, must include the following acknowlegement:
   *  "This product includes software developed by the
   *  Apache Software Foundation (http://www.apache.org/)."
   *  Alternately, this acknowlegement may appear in the software itself,
   *  if and wherever such third-party acknowlegements normally appear.
   *
   *  4. The names "The Jakarta Project", "Ant", and "Apache Software
   *  Foundation" must not be used to endorse or promote products derived
   *  from this software without prior written permission. For written
   *  permission, please contact apache@apache.org.
   *
   *  5. Products derived from this software may not be called "Apache"
   *  nor may "Apache" appear in their names without prior written
   *  permission of the Apache Group.
   *
   *  THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
   *  WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
   *  OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
   *  DISCLAIMED.  IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
   *  ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
   *  SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
   *  LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
   *  USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
   *  ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
   *  OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
   *  OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   *  SUCH DAMAGE.
   *  ====================================================================
   *
   *  This software consists of voluntary contributions made by many
   *  individuals on behalf of the Apache Software Foundation.  For more
   *  information on the Apache Software Foundation, please see
   *  <http://www.apache.org/>.
   */
  
  package org.apache.tools.ant.util;
  
  import java.lang.ref.WeakReference;
  
  /**
   * this is a weak reference on java1.2 and up, a hard
   * reference on java1.1
   * @since ant1.6
   */
  public abstract class WeakishReference  {
  
  
      /**
       * create the appropriate type of reference for the java version
       * @param object
       * @return
       */
      public static WeakishReference createReference(Object object) {
          if(JavaEnvUtils.isJavaVersion(JavaEnvUtils.JAVA_1_1)) {
              return new HardReference(object);
          } else {
              return new SoftReference(object);
          }
      }
  
      /**
       * Returns this reference object's referent.  If this reference object has
       * been cleared, then this method returns <code>null</code>.
       *
       * @return	 The object to which this reference refers, or
       *		 <code>null</code> if this reference object has been cleared
       */
      public abstract Object get();
  
      /**
       * A hard reference for Java 1.1
       */
      private static class HardReference extends WeakishReference {
          private Object object;
  
          /**
           * construct
           * @param object
           */
          public HardReference(Object object) {
              this.object = object;
          }
  
          /**
           * Returns this reference object's referent.
           */
          public Object get() {
              return object;
          }
      }
  
      /**
       * a soft reference for Java 1.2 or later
       */
      private static class SoftReference extends WeakishReference {
          private WeakReference weakref;
  
          /**
           * create a new soft reference, which is bound to a
           * Weak reference inside
           * @param reference
           * @see java.lang.ref.WeakReference
           */
          public SoftReference(Object reference) {
              this.weakref = new WeakReference(reference);
          }
  
          /**
           * Returns this reference object's referent.
           */
          public Object get() {
              return weakref.get();
          }
      }
  }
  
  
  

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