1 files changed, 138 insertions, 0 deletions
diff --git a/libjava/classpath/gnu/java/util/DoubleEnumeration.java b/libjava/classpath/gnu/java/util/DoubleEnumeration.java
new file mode 100644
index 0000000..1fc37f8
--- /dev/null
+++ b/libjava/classpath/gnu/java/util/DoubleEnumeration.java
@@ -0,0 +1,138 @@
+/* gnu.java.util.DoubleEnumeration
+   Copyright (C) 1998, 1999, 2001 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.util;
+
+import java.util.Enumeration;
+import java.util.NoSuchElementException;
+
+
+/**
+ * This is a helper class that combines two Enumerations.
+ * It returns the elements of the first Enumeration until it has
+ * no more elements and then returns the elements of the second
+ * Enumeration.<br>
+ * 
+ * In the default case:
+ * <pre>
+ * doubleEnum = new DoubleEnumeration(enum1, enum2);
+ * while (doubleEnum.hasMoreElements()) {
+ *    Object o = doubleEnum.nextElement();
+ *    do_something(o);
+ * }
+ * </pre>
+ * it calls hasMoreElements of the Enumerations as few times as
+ * possible.
+ * The references to the Enumerations are cleared as soon as they have no
+ * more elements to help garbage collecting.
+ *
+ * @author Jochen Hoenicke
+ * @author Mark Wielaard (mark@klomp.org)
+ */
+public class DoubleEnumeration implements Enumeration
+{
+  /**
+   * This is true as long as one of the enumerations has more
+   * elements.  
+   * Only valid when hasChecked is true.
+   * Set in <code>hasMoreElements()</code>
+   */
+  private boolean hasMore;
+  /**
+   * This is true, if it is sure that hasMore indicates wether there are
+   * more elements.
+   * Set to true in <code>hasMoreElements()</code>.
+   * Set to false in <code>getNextElement()</code>.
+   */
+  private boolean hasChecked;
+  /**
+   * The first enumeration.
+   */
+  private Enumeration e1;
+  /**
+   * The second enumeration.
+   */
+  private Enumeration e2;
+
+  /**
+   * Creates a new Enumeration combining the given two enumerations.
+   * The enumerations mustn't be accessed by other classes.
+   */
+  public DoubleEnumeration(Enumeration e1, Enumeration e2)
+  {
+    this.e1 = e1;
+    this.e2 = e2;
+    hasChecked = false;
+  }
+
+  /**
+   * Returns true, if at least one of the two enumerations has more
+   * elements.
+   */
+  public boolean hasMoreElements()
+  {
+    if (hasChecked)
+      return hasMore;
+
+    hasMore = (e1 != null && e1.hasMoreElements());
+
+    if (!hasMore) {
+      e1 = e2;
+      e2 = null;
+      hasMore = (e1 != null && e1.hasMoreElements());
+    }
+
+    hasChecked = true;
+    return hasMore;
+  }
+
+  /**
+   * Returns the next element.  This returns the next element of the
+   * first enumeration, if it has more elements, otherwise the next
+   * element of the second enumeration. If both enumeration don't have
+   * any elements it throws a <code>NoSuchElementException</code>.
+   */
+  public Object nextElement()
+  {
+    if (!hasMoreElements())
+      throw new NoSuchElementException();
+    else {
+      hasChecked = false;
+      return e1.nextElement();
+    }
+  }
+}