01: /*
02: * (c) Copyright 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008 Hewlett-Packard Development Company, LP
03: * All rights reserved.
04: *
05: * Redistribution and use in source and binary forms, with or without
06: * modification, are permitted provided that the following conditions
07: * are met:
08: * 1. Redistributions of source code must retain the above copyright
09: * notice, this list of conditions and the following disclaimer.
10: * 2. Redistributions in binary form must reproduce the above copyright
11: * notice, this list of conditions and the following disclaimer in the
12: * documentation and/or other materials provided with the distribution.
13: * 3. The name of the author may not be used to endorse or promote products
14: * derived from this software without specific prior written permission.
15:
16: * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
17: * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
18: * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
19: * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
20: * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
21: * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
22: * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
23: * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
24: * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
25: * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
26: *
27: * $Id: LateBindingIterator.java,v 1.6 2008/01/02 12:07:35 andy_seaborne Exp $
28: *
29: *
30: * LateBindingIterator.java
31: *
32: * Created on June 16, 2001, 8:19 PM
33: */
34:
35: package com.hp.hpl.jena.util.iterator;
36:
37: import java.util.Iterator;
38:
39: /** An Iterator that is created lazily.
40: * The sequence to be defined is defined by
41: * the subclass's definition of create().
42: * This is only called on the first call to
43: * <CODE>hasNext()</CODE> or <CODE>next()</CODE>.
44: * This allows an Iterator to be passed to some other
45: * code, while delaying the evaluation of what actually
46: * is going to be iterated over.
47: * @author jjc
48: * @version Release='$Name: $' Revision='$Revision: 1.6 $' Date='$Date: 2008/01/02 12:07:35 $'
49: */
50: abstract public class LateBindingIterator implements Iterator {
51:
52: private Iterator it;
53:
54: /** An Iterator that is created lazily.
55: * The sequence to be defined is defined by
56: * a subclass's instantiation of create().
57: * This is only called on the first call to
58: * <CODE>hasNext()</CODE> or <CODE>next()</CODE>.
59: */
60: public LateBindingIterator() {
61: }
62:
63: public boolean hasNext() {
64: lazy();
65: return it.hasNext();
66: }
67:
68: public Object next() {
69: lazy();
70: return it.next();
71: }
72:
73: public void remove() {
74: lazy();
75: it.remove();
76: }
77:
78: private void lazy() {
79: if (it == null)
80: it = create();
81: }
82:
83: /** The subclass must define this to return
84: * the Iterator to invoke. This method will be
85: * called at most once, on the first call to
86: * <CODE>next()</CODE> or <CODE>hasNext()</CODE>.
87: * From then on, all calls to this will be passed
88: * through to the returned Iterator.
89: * @return The parent iterator defining the sequence.
90: */
91: public abstract Iterator create();
92:
93: }
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