1 // ========================================================================
2 // Copyright (c) 2004-2009 Mort Bay Consulting Pty. Ltd.
3 // ------------------------------------------------------------------------
4 // All rights reserved. This program and the accompanying materials
5 // are made available under the terms of the Eclipse Public License v1.0
6 // and Apache License v2.0 which accompanies this distribution.
7 // The Eclipse Public License is available at
8 // http://www.eclipse.org/legal/epl-v10.html
9 // The Apache License v2.0 is available at
10 // http://www.opensource.org/licenses/apache2.0.php
11 // You may elect to redistribute this code under either of these licenses.
12 // ========================================================================
13
14 package org.eclipse.jetty.util;
15 import java.io.Serializable;
16 import java.lang.reflect.Array;
17 import java.util.ArrayList;
18 import java.util.Arrays;
19 import java.util.Collection;
20 import java.util.Collections;
21 import java.util.Iterator;
22 import java.util.List;
23 import java.util.ListIterator;
24
25 /* ------------------------------------------------------------ */
26 /** Lazy List creation.
27 * A List helper class that attempts to avoid unnecessary List
28 * creation. If a method needs to create a List to return, but it is
29 * expected that this will either be empty or frequently contain a
30 * single item, then using LazyList will avoid additional object
31 * creations by using Collections.EMPTY_LIST or
32 * Collections.singletonList where possible.
33 * <p>
34 * LazyList works by passing an opaque representation of the list in
35 * and out of all the LazyList methods. This opaque object is either
36 * null for an empty list, an Object for a list with a single entry
37 * or an ArrayList<Object> for a list of items.
38 *
39 * <p><h4>Usage</h4>
40 * <pre>
41 * Object lazylist =null;
42 * while(loopCondition)
43 * {
44 * Object item = getItem();
45 * if (item.isToBeAdded())
46 * lazylist = LazyList.add(lazylist,item);
47 * }
48 * return LazyList.getList(lazylist);
49 * </pre>
50 *
51 * An ArrayList of default size is used as the initial LazyList.
52 *
53 * @see java.util.List
54 */
55 public class LazyList
56 implements Cloneable, Serializable
57 {
58 private static final String[] __EMTPY_STRING_ARRAY = new String[0];
59
60 /* ------------------------------------------------------------ */
61 private LazyList()
62 {}
63
64 /* ------------------------------------------------------------ */
65 /** Add an item to a LazyList
66 * @param list The list to add to or null if none yet created.
67 * @param item The item to add.
68 * @return The lazylist created or added to.
69 */
70 @SuppressWarnings("unchecked")
71 public static Object add(Object list, Object item)
72 {
73 if (list==null)
74 {
75 if (item instanceof List || item==null)
76 {
77 List<Object> l = new ArrayList<Object>();
78 l.add(item);
79 return l;
80 }
81
82 return item;
83 }
84
85 if (list instanceof List)
86 {
87 ((List<Object>)list).add(item);
88 return list;
89 }
90
91 List<Object> l=new ArrayList<Object>();
92 l.add(list);
93 l.add(item);
94 return l;
95 }
96
97 /* ------------------------------------------------------------ */
98 /** Add an item to a LazyList
99 * @param list The list to add to or null if none yet created.
100 * @param index The index to add the item at.
101 * @param item The item to add.
102 * @return The lazylist created or added to.
103 */
104 @SuppressWarnings("unchecked")
105 public static Object add(Object list, int index, Object item)
106 {
107 if (list==null)
108 {
109 if (index>0 || item instanceof List || item==null)
110 {
111 List<Object> l = new ArrayList<Object>();
112 l.add(index,item);
113 return l;
114 }
115 return item;
116 }
117
118 if (list instanceof List)
119 {
120 ((List<Object>)list).add(index,item);
121 return list;
122 }
123
124 List<Object> l=new ArrayList<Object>();
125 l.add(list);
126 l.add(index,item);
127 return l;
128 }
129
130 /* ------------------------------------------------------------ */
131 /** Add the contents of a Collection to a LazyList
132 * @param list The list to add to or null if none yet created.
133 * @param collection The Collection whose contents should be added.
134 * @return The lazylist created or added to.
135 */
136 public static Object addCollection(Object list, Collection<?> collection)
137 {
138 Iterator<?> i=collection.iterator();
139 while(i.hasNext())
140 list=LazyList.add(list,i.next());
141 return list;
142 }
143
144 /* ------------------------------------------------------------ */
145 /** Add the contents of an array to a LazyList
146 * @param list The list to add to or null if none yet created.
147 * @param array The array whose contents should be added.
148 * @return The lazylist created or added to.
149 */
150 public static Object addArray(Object list, Object[] array)
151 {
152 for(int i=0;array!=null && i<array.length;i++)
153 list=LazyList.add(list,array[i]);
154 return list;
155 }
156
157 /* ------------------------------------------------------------ */
158 /** Ensure the capcity of the underlying list.
159 *
160 */
161 public static Object ensureSize(Object list, int initialSize)
162 {
163 if (list==null)
164 return new ArrayList<Object>(initialSize);
165 if (list instanceof ArrayList)
166 {
167 ArrayList<?> ol=(ArrayList<?>)list;
168 if (ol.size()>initialSize)
169 return ol;
170 ArrayList<Object> nl = new ArrayList<Object>(initialSize);
171 nl.addAll(ol);
172 return nl;
173 }
174 List<Object> l= new ArrayList<Object>(initialSize);
175 l.add(list);
176 return l;
177 }
178
179 /* ------------------------------------------------------------ */
180 public static Object remove(Object list, Object o)
181 {
182 if (list==null)
183 return null;
184
185 if (list instanceof List)
186 {
187 List<?> l = (List<?>)list;
188 l.remove(o);
189 if (l.size()==0)
190 return null;
191 return list;
192 }
193
194 if (list.equals(o))
195 return null;
196 return list;
197 }
198
199 /* ------------------------------------------------------------ */
200 public static Object remove(Object list, int i)
201 {
202 if (list==null)
203 return null;
204
205 if (list instanceof List)
206 {
207 List<?> l = (List<?>)list;
208 l.remove(i);
209 if (l.size()==0)
210 return null;
211 return list;
212 }
213
214 if (i==0)
215 return null;
216 return list;
217 }
218
219
220
221 /* ------------------------------------------------------------ */
222 /** Get the real List from a LazyList.
223 *
224 * @param list A LazyList returned from LazyList.add(Object)
225 * @return The List of added items, which may be an EMPTY_LIST
226 * or a SingletonList.
227 */
228 public static<E> List<E> getList(Object list)
229 {
230 return getList(list,false);
231 }
232
233
234 /* ------------------------------------------------------------ */
235 /** Get the real List from a LazyList.
236 *
237 * @param list A LazyList returned from LazyList.add(Object) or null
238 * @param nullForEmpty If true, null is returned instead of an
239 * empty list.
240 * @return The List of added items, which may be null, an EMPTY_LIST
241 * or a SingletonList.
242 */
243 @SuppressWarnings("unchecked")
244 public static<E> List<E> getList(Object list, boolean nullForEmpty)
245 {
246 if (list==null)
247 {
248 if (nullForEmpty)
249 return null;
250 return Collections.emptyList();
251 }
252 if (list instanceof List)
253 return (List<E>)list;
254
255 return (List<E>)Collections.singletonList(list);
256 }
257
258
259 /* ------------------------------------------------------------ */
260 public static String[] toStringArray(Object list)
261 {
262 if (list==null)
263 return __EMTPY_STRING_ARRAY;
264
265 if (list instanceof List)
266 {
267 List<?> l = (List<?>)list;
268 String[] a = new String[l.size()];
269 for (int i=l.size();i-->0;)
270 {
271 Object o=l.get(i);
272 if (o!=null)
273 a[i]=o.toString();
274 }
275 return a;
276 }
277
278 return new String[] {list.toString()};
279 }
280
281 /* ------------------------------------------------------------ */
282 /** Convert a lazylist to an array
283 * @param list The list to convert
284 * @param clazz The class of the array, which may be a primitive type
285 * @return array of the lazylist entries passed in
286 */
287 @SuppressWarnings("unchecked")
288 public static Object toArray(Object list,Class<?> clazz)
289 {
290 if (list==null)
291 return Array.newInstance(clazz,0);
292
293 if (list instanceof List)
294 {
295 List<?> l = (List<?>)list;
296 if (clazz.isPrimitive())
297 {
298 Object a = Array.newInstance(clazz,l.size());
299 for (int i=0;i<l.size();i++)
300 Array.set(a,i,l.get(i));
301 return a;
302 }
303 return l.toArray((Object[])Array.newInstance(clazz,l.size()));
304
305 }
306
307 Object a = Array.newInstance(clazz,1);
308 Array.set(a,0,list);
309 return a;
310 }
311
312 /* ------------------------------------------------------------ */
313 /** The size of a lazy List
314 * @param list A LazyList returned from LazyList.add(Object) or null
315 * @return the size of the list.
316 */
317 public static int size(Object list)
318 {
319 if (list==null)
320 return 0;
321 if (list instanceof List)
322 return ((List<?>)list).size();
323 return 1;
324 }
325
326 /* ------------------------------------------------------------ */
327 /** Get item from the list
328 * @param list A LazyList returned from LazyList.add(Object) or null
329 * @param i int index
330 * @return the item from the list.
331 */
332 @SuppressWarnings("unchecked")
333 public static <E> E get(Object list, int i)
334 {
335 if (list==null)
336 throw new IndexOutOfBoundsException();
337
338 if (list instanceof List)
339 return (E)((List<?>)list).get(i);
340
341 if (i==0)
342 return (E)list;
343
344 throw new IndexOutOfBoundsException();
345 }
346
347 /* ------------------------------------------------------------ */
348 public static boolean contains(Object list,Object item)
349 {
350 if (list==null)
351 return false;
352
353 if (list instanceof List)
354 return ((List<?>)list).contains(item);
355
356 return list.equals(item);
357 }
358
359
360 /* ------------------------------------------------------------ */
361 public static Object clone(Object list)
362 {
363 if (list==null)
364 return null;
365 if (list instanceof List)
366 return new ArrayList<Object>((List<?>)list);
367 return list;
368 }
369
370 /* ------------------------------------------------------------ */
371 public static String toString(Object list)
372 {
373 if (list==null)
374 return "[]";
375 if (list instanceof List)
376 return list.toString();
377 return "["+list+"]";
378 }
379
380 /* ------------------------------------------------------------ */
381 @SuppressWarnings("unchecked")
382 public static<E> Iterator<E> iterator(Object list)
383 {
384 if (list==null)
385 {
386 List<E> empty=Collections.emptyList();
387 return empty.iterator();
388 }
389 if (list instanceof List)
390 {
391 return ((List<E>)list).iterator();
392 }
393 List<E> l=getList(list);
394 return l.iterator();
395 }
396
397 /* ------------------------------------------------------------ */
398 @SuppressWarnings("unchecked")
399 public static<E> ListIterator<E> listIterator(Object list)
400 {
401 if (list==null)
402 {
403 List<E> empty=Collections.emptyList();
404 return empty.listIterator();
405 }
406 if (list instanceof List)
407 return ((List<E>)list).listIterator();
408
409 List<E> l=getList(list);
410 return l.listIterator();
411 }
412
413 /* ------------------------------------------------------------ */
414 /**
415 * @param array Any array of object
416 * @return A new <i>modifiable</i> list initialised with the elements from <code>array</code>.
417 */
418 public static<E> List<E> array2List(E[] array)
419 {
420 if (array==null || array.length==0)
421 return new ArrayList<E>();
422 return new ArrayList<E>(Arrays.asList(array));
423 }
424
425 /* ------------------------------------------------------------ */
426 /** Add element to an array
427 * @param array The array to add to (or null)
428 * @param item The item to add
429 * @param type The type of the array (in case of null array)
430 * @return new array with contents of array plus item
431 */
432 @SuppressWarnings("unchecked")
433 public static Object[] addToArray(Object[] array, Object item, Class<?> type)
434 {
435 if (array==null)
436 {
437 if (type==null && item!=null)
438 type= item.getClass();
439 Object[] na = (Object[])Array.newInstance(type, 1);
440 na[0]=item;
441 return na;
442 }
443 else
444 {
445 Class<?> c = array.getClass().getComponentType();
446 Object[] na = (Object[])Array.newInstance(c, Array.getLength(array)+1);
447 System.arraycopy(array, 0, na, 0, array.length);
448 na[array.length]=item;
449 return na;
450 }
451 }
452
453 /* ------------------------------------------------------------ */
454 @SuppressWarnings("unchecked")
455 public static Object removeFromArray(Object[] array, Object item)
456 {
457 if (item==null || array==null)
458 return array;
459 for (int i=array.length;i-->0;)
460 {
461 if (item.equals(array[i]))
462 {
463 Class<?> c = array==null?item.getClass():array.getClass().getComponentType();
464 Object[] na = (Object[])Array.newInstance(c, Array.getLength(array)-1);
465 if (i>0)
466 System.arraycopy(array, 0, na, 0, i);
467 if (i+1<array.length)
468 System.arraycopy(array, i+1, na, i, array.length-(i+1));
469 return na;
470 }
471 }
472 return array;
473 }
474
475 }
476