libjava/classpath/gnu/java/beans/encoder/elements/Element.java

   1 /* Element.java -- Base class for object tree elements.
   2    Copyright (C) 2005 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., 51 Franklin Street, Fifth Floor, Boston, MA
  19 02110-1301 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
  38
  39 package gnu.java.beans.encoder.elements;
  40
  41 import java.util.Iterator;
  42 import java.util.LinkedList;
  43
  44 import gnu.java.beans.encoder.ObjectId;
  45 import gnu.java.beans.encoder.Writer;
  46
  47 /** <code>Element</code> is the base class for the object tree elements.
  48  *
  49  * <p>It provides the neccessary infrastructure every element subclass
  50  * needs in order to interact with the {@link gnu.java.beans.encoder.Root}
  51  * class.</p>
  52  *
  53  * @author Robert Schuster (robertschuster@fsfe.org)
  54  */
  55 public abstract class Element
  56 {
  57   /**
  58    * Stores the child elements.
  59    */
  60   private LinkedList children = new LinkedList();
  61
  62   /**
  63    * An optional ObjectId instance which is needed for certain subclasses
  64    * only.
  65    */
  66   private ObjectId objectId;
  67
  68   /** Sets an {@link gnu.java.beans.encoder.ObjectId} instance in this
  69    * <code>Element</code>.
  70    *
  71    * <p>This can only be done once.</p>
  72    *
  73    * @param objectId An ObjectId instance.
  74    */
  75   public final void initId(ObjectId objectId)
  76   {
  77     assert (this.objectId == null);
  78     assert (objectId != null);
  79
  80     this.objectId = objectId;
  81   }
  82
  83   /** Adds a child element to this <code>Element</code>.
  84    *
  85    * @param elem The new child.
  86    */
  87   public final void addChild(Element elem)
  88   {
  89     children.add(elem);
  90   }
  91
  92   /** Removes the child element added last.
  93    */
  94   public final void removeLast()
  95   {
  96     children.removeLast();
  97   }
  98
  99   /** Provides access to the child elements via an iterator.
 100    *
 101    * @return An iterator for the child elements.
 102    */
 103   public final Iterator iterator(){
 104     return children.iterator();
 105   }
 106
 107   /** Clears all the stored child elements.
 108    *
 109    */
 110   public final void clear()
 111   {
 112    children.clear();
 113   }
 114
 115   /** Returns whether this element contains child elements.
 116    *
 117    * <p>This method is useful to decide which formatting variant
 118    * for the XML element can be chosen.</p>
 119    *
 120    * @return Whether the element has child elements.
 121    */
 122   public final boolean isEmpty()
 123   {
 124     return children.isEmpty();
 125   }
 126
 127   /** Retrieves the element's {@link gnu.java.beans.encoder.ObjectId} instance
 128    * if it has one.
 129    *
 130    * @return The ObjectId instance or <code>null</code>.
 131    */
 132   public final ObjectId getId()
 133   {
 134     return objectId;
 135   }
 136
 137   /** Writes the opening XML tag.
 138    *
 139    * @param writer The writer to be used for XML writing.
 140    */
 141   public abstract void writeStart(Writer writer);
 142
 143   /** Writes the closing XML tag.
 144    *
 145    * <p>By default this does <code>writer.writeEnd(children.isEmpty())</code>.
 146    * Override if neccessary, for example when using the
 147    * {@link gnu.java.beans.encoder.Writer#writeNoChildren}</code> method
 148    * variants.
 149    *
 150    * @param writer The writer to be used for XML writing.
 151    */
 152   public void writeEnd(Writer writer)
 153   {
 154     writer.writeEnd(children.isEmpty());
 155   }
 156
 157 }