Created an iterator that iterates over iterators.

git-svn-id: https://samskivert.googlecode.com/svn/trunk@458 6335cc39-0255-0410-8fd6-9bcaacd3b74c
2001-11-20 03:35:53 +00:00
parent 9e11a32409
commit 5cbee6d365
1 changed files with 104 additions and 0 deletions
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+//
+// $Id: CompoundIterator.java,v 1.1 2001/11/20 03:35:53 mdb Exp $
+//
+// samskivert library - useful routines for java programs
+// Copyright (C) 2001 Michael Bayne
+// 
+// This library is free software; you can redistribute it and/or modify it
+// under the terms of the GNU Lesser General Public License as published
+// by the Free Software Foundation; either version 2.1 of the License, or
+// (at your option) any later version.
+//
+// This library 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
+// Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public
+// License along with this library; if not, write to the Free Software
+// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+
+package com.samskivert.util;
+
+import java.util.Iterator;
+import java.util.NoSuchElementException;
+
+/**
+ * Iterates over a collection of iterators, moving seamlessly from one
+ * iterator to the next as the first runs out of elements. Iterators are
+ * made available to the compound iterator via the succinct and functional
+ * {@link IteratorProvider} interface.
+ */
+public class CompoundIterator implements Iterator
+{
+    /** Used to obtain the set of iterators over which we will iterate. */
+    public static interface IteratorProvider
+    {
+        /**
+         * Returns the next iterator in the set. Should return null when
+         * we've run out of iterators.
+         */
+        public Iterator nextIterator ();
+    }
+
+    /**
+     * Constructs a compound iterator that will iterate over all of the
+     * iterators provided by the supplied provider, in turn.
+     */
+    public CompoundIterator (IteratorProvider provider)
+    {
+        _provider = provider;
+        // move to the first iterator
+        _iter = _provider.nextIterator();
+    }
+
+    // documentation inherited
+    public boolean hasNext ()
+    {
+        // keep trying iterators until we run out or find an element
+        while (_iter != null) {
+            try {
+                if (_iter.hasNext()) {
+                    return true;
+                }
+            } catch (NoSuchElementException nsee) {
+                // have to catch this and move to the next iterator
+                _iter = _provider.nextIterator();
+            }
+        }
+
+        return false;
+    }
+
+    // documentation inherited
+    public Object next ()
+    {
+        // keep trying iterators until we run out or find an element
+        while (_iter != null) {
+            try {
+                return _iter.next();
+            } catch (NoSuchElementException nsee) {
+                // have to catch this and move to the next iterator
+                _iter = _provider.nextIterator();
+            }
+        }
+
+        throw new NoSuchElementException();
+    }
+
+    // documentation inherited
+    public void remove ()
+    {
+        if (_iter != null) {
+            _iter.remove();
+        } else {
+            throw new IllegalStateException();
+        }
+    }
+
+    /** Our provider of iterators. */
+    protected IteratorProvider _provider;
+
+    /** The iterator currently in use. */
+    protected Iterator _iter;
+}