libjava/gnu/java/beans/decoder/AbstractCreatableObjectContext.java

   1 /* gnu.java.beans.decoder.AbstractCreatableContext
   2    Copyright (C) 2004 Free Software Foundation, Inc.
   3
   4 This file is part of GNU Classpath.
   5
   6 GNU Classpath is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 2, or (at your option)
   9 any later version.
  10
  11 GNU Classpath is distributed in the hope that it will be useful, but
  12 WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GNU Classpath; see the file COPYING.  If not, write to the
  18 Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  19 02111-1307 USA.
  20
  21 Linking this library statically or dynamically with other modules is
  22 making a combined work based on this library.  Thus, the terms and
  23 conditions of the GNU General Public License cover the whole
  24 combination.
  25
  26 As a special exception, the copyright holders of this library give you
  27 permission to link this library with independent modules to produce an
  28 executable, regardless of the license terms of these independent
  29 modules, and to copy and distribute the resulting executable under
  30 terms of your choice, provided that you also meet, for each linked
  31 independent module, the terms and conditions of the license of that
  32 module.  An independent module is a module which is not derived from
  33 or based on this library.  If you modify this library, you may extend
  34 this exception to your version of the library, but you are not
  35 obligated to do so.  If you do not wish to do so, delete this
  36 exception statement from your version. */
  37 package gnu.java.beans.decoder;
  38
  39
  40 /** AbstractCreatableObjectContext is the base class for all Context implementations
  41  * which create a result object in their lifetime. It provides means for preventing
  42  * to create the object twice.
  43  *
  44  * @author Robert Schuster
  45  *
  46  */
  47 abstract class AbstractCreatableObjectContext extends AbstractObjectContext
  48 {
  49   AbstractCreatableObjectContext()
  50   {
  51   }
  52
  53   /** Adds a parameter object to this Context if the result object has not been
  54    * created yet. Otherwise an AssemblyException is thrown that indicates a wrong
  55    * behavior of the decoder.
  56    */
  57   public final void addParameterObject(Object o) throws AssemblyException
  58   {
  59     if (object == null)
  60       addParameterObjectImpl(o);
  61     else
  62       throw new AssemblyException(new IllegalStateException("No more parameter objects are allowed when the object as already been created."));
  63   }
  64
  65   /** Adds a parameter object to this Context. Implement this without caring
  66    * for illegal states because this has been done already.
  67    *
  68    * @param obj The parameter object to be added.
  69    */
  70   protected abstract void addParameterObjectImpl(Object obj);
  71
  72   /** Creates the result object if it does not exist already.
  73    */
  74   public final void notifyStatement(Context outerContext)
  75     throws AssemblyException
  76   {
  77     if (object != null)
  78       return;
  79
  80     object = createObject(outerContext);
  81   }
  82
  83   /** Creates the result object. This method is called only once. Implement this
  84    * without checking for double invocations as this is already being prevented.
  85    *
  86    * @param outerContext The Context that exists around this one.
  87    * @return The result object.
  88    * @throws AssemblerException if the object creation fails somehow.
  89    */
  90   protected abstract Object createObject(Context outerContext)
  91     throws AssemblyException;
  92
  93   /* (non-Javadoc)
  94    * @see gnu.java.beans.decoder.Context#endContext(gnu.java.beans.decoder.Context)
  95    */
  96   public final Object endContext(Context outerContext)
  97     throws AssemblyException
  98   {
  99     notifyStatement(outerContext);
 100     return object;
 101   }
 102
 103   /* (non-Javadoc)
 104    * @see gnu.java.beans.decoder.Context#subContextFailed()
 105    */
 106   public boolean subContextFailed()
 107   {
 108     /* Returns true when the AbstractCreatableObjectContext has not created the result object yet
 109      * (A failed subcontext automatically lets this context fail too.)
 110      */
 111     return object == null;
 112   }
 113 }