Initial revision

From-SVN: r102074

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

@@ -0,0 +1,113 @@
+/* gnu.java.beans.decoder.AbstractCreatableContext
+   Copyright (C) 2004 Free Software Foundation, Inc.
+
+This file is part of GNU Classpath.
+
+GNU Classpath is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2, or (at your option)
+any later version.
+ 
+GNU Classpath 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 for more details.
+
+You should have received a copy of the GNU General Public License
+along with GNU Classpath; see the file COPYING.  If not, write to the
+Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+02110-1301 USA.
+
+Linking this library statically or dynamically with other modules is
+making a combined work based on this library.  Thus, the terms and
+conditions of the GNU General Public License cover the whole
+combination.
+
+As a special exception, the copyright holders of this library give you
+permission to link this library with independent modules to produce an
+executable, regardless of the license terms of these independent
+modules, and to copy and distribute the resulting executable under
+terms of your choice, provided that you also meet, for each linked
+independent module, the terms and conditions of the license of that
+module.  An independent module is a module which is not derived from
+or based on this library.  If you modify this library, you may extend
+this exception to your version of the library, but you are not
+obligated to do so.  If you do not wish to do so, delete this
+exception statement from your version. */
+package gnu.java.beans.decoder;
+
+
+/** AbstractCreatableObjectContext is the base class for all Context implementations
+ * which create a result object in their lifetime. It provides means for preventing
+ * to create the object twice.
+ *
+ * @author Robert Schuster
+ *
+ */
+abstract class AbstractCreatableObjectContext extends AbstractObjectContext
+{
+  AbstractCreatableObjectContext()
+  {
+  }
+
+  /** Adds a parameter object to this Context if the result object has not been
+   * created yet. Otherwise an AssemblyException is thrown that indicates a wrong
+   * behavior of the decoder.
+   */
+  public final void addParameterObject(Object o) throws AssemblyException
+  {
+    if (object == null)
+      addParameterObjectImpl(o);
+    else
+      throw new AssemblyException(new IllegalStateException("No more parameter objects are allowed when the object as already been created."));
+  }
+
+  /** Adds a parameter object to this Context. Implement this without caring
+   * for illegal states because this has been done already.
+   *
+   * @param obj The parameter object to be added. 
+   */
+  protected abstract void addParameterObjectImpl(Object obj);
+
+  /** Creates the result object if it does not exist already.
+   */
+  public final void notifyStatement(Context outerContext)
+    throws AssemblyException
+  {
+    if (object != null)
+      return;
+
+    object = createObject(outerContext);
+  }
+
+  /** Creates the result object. This method is called only once. Implement this
+   * without checking for double invocations as this is already being prevented.
+   *
+   * @param outerContext The Context that exists around this one. 
+   * @return The result object.
+   * @throws AssemblerException if the object creation fails somehow.
+   */
+  protected abstract Object createObject(Context outerContext)
+    throws AssemblyException;
+
+  /* (non-Javadoc)
+   * @see gnu.java.beans.decoder.Context#endContext(gnu.java.beans.decoder.Context)
+   */
+  public final Object endContext(Context outerContext)
+    throws AssemblyException
+  {
+    notifyStatement(outerContext);
+    return object;
+  }
+
+  /* (non-Javadoc)
+   * @see gnu.java.beans.decoder.Context#subContextFailed()
+   */
+  public boolean subContextFailed()
+  {
+    /* Returns true when the AbstractCreatableObjectContext has not created the result object yet
+     * (A failed subcontext automatically lets this context fail too.)
+     */
+    return object == null;
+  }
+}