001 /*
002 * Copyright (C) 2007 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017 package com.google.common.base;
018
019 import com.google.common.annotations.GwtCompatible;
020 import com.google.common.annotations.VisibleForTesting;
021
022 import java.util.NoSuchElementException;
023
024 import javax.annotation.Nullable;
025
026 /**
027 * Simple static methods to be called at the start of your own methods to verify
028 * correct arguments and state. This allows constructs such as
029 * <pre>
030 * if (count <= 0) {
031 * throw new IllegalArgumentException("must be positive: " + count);
032 * }</pre>
033 *
034 * to be replaced with the more compact
035 * <pre>
036 * checkArgument(count > 0, "must be positive: %s", count);</pre>
037 *
038 * Note that the sense of the expression is inverted; with {@code Preconditions}
039 * you declare what you expect to be <i>true</i>, just as you do with an
040 * <a href="http://java.sun.com/j2se/1.5.0/docs/guide/language/assert.html">
041 * {@code assert}</a> or a JUnit {@code assertTrue} call.
042 *
043 * <p><b>Warning:</b> only the {@code "%s"} specifier is recognized as a
044 * placeholder in these messages, not the full range of {@link
045 * String#format(String, Object[])} specifiers.
046 *
047 * <p>Take care not to confuse precondition checking with other similar types
048 * of checks! Precondition exceptions -- including those provided here, but also
049 * {@link IndexOutOfBoundsException}, {@link NoSuchElementException}, {@link
050 * UnsupportedOperationException} and others -- are used to signal that the
051 * <i>calling method</i> has made an error. This tells the caller that it should
052 * not have invoked the method when it did, with the arguments it did, or
053 * perhaps ever. Postcondition or other invariant failures should not throw
054 * these types of exceptions.
055 *
056 * @author Kevin Bourrillion
057 * @since 2 (imported from Google Collections Library)
058 */
059 @GwtCompatible
060 public final class Preconditions {
061 private Preconditions() {}
062
063 /**
064 * Ensures the truth of an expression involving one or more parameters to the
065 * calling method.
066 *
067 * @param expression a boolean expression
068 * @throws IllegalArgumentException if {@code expression} is false
069 */
070 public static void checkArgument(boolean expression) {
071 if (!expression) {
072 throw new IllegalArgumentException();
073 }
074 }
075
076 /**
077 * Ensures the truth of an expression involving one or more parameters to the
078 * calling method.
079 *
080 * @param expression a boolean expression
081 * @param errorMessage the exception message to use if the check fails; will
082 * be converted to a string using {@link String#valueOf(Object)}
083 * @throws IllegalArgumentException if {@code expression} is false
084 */
085 public static void checkArgument(
086 boolean expression, @Nullable Object errorMessage) {
087 if (!expression) {
088 throw new IllegalArgumentException(String.valueOf(errorMessage));
089 }
090 }
091
092 /**
093 * Ensures the truth of an expression involving one or more parameters to the
094 * calling method.
095 *
096 * @param expression a boolean expression
097 * @param errorMessageTemplate a template for the exception message should the
098 * check fail. The message is formed by replacing each {@code %s}
099 * placeholder in the template with an argument. These are matched by
100 * position - the first {@code %s} gets {@code errorMessageArgs[0]}, etc.
101 * Unmatched arguments will be appended to the formatted message in square
102 * braces. Unmatched placeholders will be left as-is.
103 * @param errorMessageArgs the arguments to be substituted into the message
104 * template. Arguments are converted to strings using
105 * {@link String#valueOf(Object)}.
106 * @throws IllegalArgumentException if {@code expression} is false
107 * @throws NullPointerException if the check fails and either {@code
108 * errorMessageTemplate} or {@code errorMessageArgs} is null (don't let
109 * this happen)
110 */
111 public static void checkArgument(boolean expression,
112 @Nullable String errorMessageTemplate,
113 @Nullable Object... errorMessageArgs) {
114 if (!expression) {
115 throw new IllegalArgumentException(
116 format(errorMessageTemplate, errorMessageArgs));
117 }
118 }
119
120 /**
121 * Ensures the truth of an expression involving the state of the calling
122 * instance, but not involving any parameters to the calling method.
123 *
124 * @param expression a boolean expression
125 * @throws IllegalStateException if {@code expression} is false
126 */
127 public static void checkState(boolean expression) {
128 if (!expression) {
129 throw new IllegalStateException();
130 }
131 }
132
133 /**
134 * Ensures the truth of an expression involving the state of the calling
135 * instance, but not involving any parameters to the calling method.
136 *
137 * @param expression a boolean expression
138 * @param errorMessage the exception message to use if the check fails; will
139 * be converted to a string using {@link String#valueOf(Object)}
140 * @throws IllegalStateException if {@code expression} is false
141 */
142 public static void checkState(
143 boolean expression, @Nullable Object errorMessage) {
144 if (!expression) {
145 throw new IllegalStateException(String.valueOf(errorMessage));
146 }
147 }
148
149 /**
150 * Ensures the truth of an expression involving the state of the calling
151 * instance, but not involving any parameters to the calling method.
152 *
153 * @param expression a boolean expression
154 * @param errorMessageTemplate a template for the exception message should the
155 * check fail. The message is formed by replacing each {@code %s}
156 * placeholder in the template with an argument. These are matched by
157 * position - the first {@code %s} gets {@code errorMessageArgs[0]}, etc.
158 * Unmatched arguments will be appended to the formatted message in square
159 * braces. Unmatched placeholders will be left as-is.
160 * @param errorMessageArgs the arguments to be substituted into the message
161 * template. Arguments are converted to strings using
162 * {@link String#valueOf(Object)}.
163 * @throws IllegalStateException if {@code expression} is false
164 * @throws NullPointerException if the check fails and either {@code
165 * errorMessageTemplate} or {@code errorMessageArgs} is null (don't let
166 * this happen)
167 */
168 public static void checkState(boolean expression,
169 @Nullable String errorMessageTemplate,
170 @Nullable Object... errorMessageArgs) {
171 if (!expression) {
172 throw new IllegalStateException(
173 format(errorMessageTemplate, errorMessageArgs));
174 }
175 }
176
177 /**
178 * Ensures that an object reference passed as a parameter to the calling
179 * method is not null.
180 *
181 * @param reference an object reference
182 * @return the non-null reference that was validated
183 * @throws NullPointerException if {@code reference} is null
184 */
185 public static <T> T checkNotNull(T reference) {
186 if (reference == null) {
187 throw new NullPointerException();
188 }
189 return reference;
190 }
191
192 /**
193 * Ensures that an object reference passed as a parameter to the calling
194 * method is not null.
195 *
196 * @param reference an object reference
197 * @param errorMessage the exception message to use if the check fails; will
198 * be converted to a string using {@link String#valueOf(Object)}
199 * @return the non-null reference that was validated
200 * @throws NullPointerException if {@code reference} is null
201 */
202 public static <T> T checkNotNull(T reference, @Nullable Object errorMessage) {
203 if (reference == null) {
204 throw new NullPointerException(String.valueOf(errorMessage));
205 }
206 return reference;
207 }
208
209 /**
210 * Ensures that an object reference passed as a parameter to the calling
211 * method is not null.
212 *
213 * @param reference an object reference
214 * @param errorMessageTemplate a template for the exception message should the
215 * check fail. The message is formed by replacing each {@code %s}
216 * placeholder in the template with an argument. These are matched by
217 * position - the first {@code %s} gets {@code errorMessageArgs[0]}, etc.
218 * Unmatched arguments will be appended to the formatted message in square
219 * braces. Unmatched placeholders will be left as-is.
220 * @param errorMessageArgs the arguments to be substituted into the message
221 * template. Arguments are converted to strings using
222 * {@link String#valueOf(Object)}.
223 * @return the non-null reference that was validated
224 * @throws NullPointerException if {@code reference} is null
225 */
226 public static <T> T checkNotNull(T reference,
227 @Nullable String errorMessageTemplate,
228 @Nullable Object... errorMessageArgs) {
229 if (reference == null) {
230 // If either of these parameters is null, the right thing happens anyway
231 throw new NullPointerException(
232 format(errorMessageTemplate, errorMessageArgs));
233 }
234 return reference;
235 }
236
237 /*
238 * All recent hotspots (as of 2009) *really* like to have the natural code
239 *
240 * if (guardExpression) {
241 * throw new BadException(messageExpression);
242 * }
243 *
244 * refactored so that messageExpression is moved to a separate
245 * String-returning method.
246 *
247 * if (guardExpression) {
248 * throw new BadException(badMsg(...));
249 * }
250 *
251 * The alternative natural refactorings into void or Exception-returning
252 * methods are much slower. This is a big deal - we're talking factors of
253 * 2-8 in microbenchmarks, not just 10-20%. (This is a hotspot optimizer
254 * bug, which should be fixed, but that's a separate, big project).
255 *
256 * The coding pattern above is heavily used in java.util, e.g. in ArrayList.
257 * There is a RangeCheckMicroBenchmark in the JDK that was used to test this.
258 *
259 * But the methods in this class want to throw different exceptions,
260 * depending on the args, so it appears that this pattern is not directly
261 * applicable. But we can use the ridiculous, devious trick of throwing an
262 * exception in the middle of the construction of another exception.
263 * Hotspot is fine with that.
264 */
265
266 /**
267 * Ensures that {@code index} specifies a valid <i>element</i> in an array,
268 * list or string of size {@code size}. An element index may range from zero,
269 * inclusive, to {@code size}, exclusive.
270 *
271 * @param index a user-supplied index identifying an element of an array, list
272 * or string
273 * @param size the size of that array, list or string
274 * @return the value of {@code index}
275 * @throws IndexOutOfBoundsException if {@code index} is negative or is not
276 * less than {@code size}
277 * @throws IllegalArgumentException if {@code size} is negative
278 */
279 public static int checkElementIndex(int index, int size) {
280 return checkElementIndex(index, size, "index");
281 }
282
283 /**
284 * Ensures that {@code index} specifies a valid <i>element</i> in an array,
285 * list or string of size {@code size}. An element index may range from zero,
286 * inclusive, to {@code size}, exclusive.
287 *
288 * @param index a user-supplied index identifying an element of an array, list
289 * or string
290 * @param size the size of that array, list or string
291 * @param desc the text to use to describe this index in an error message
292 * @return the value of {@code index}
293 * @throws IndexOutOfBoundsException if {@code index} is negative or is not
294 * less than {@code size}
295 * @throws IllegalArgumentException if {@code size} is negative
296 */
297 public static int checkElementIndex(
298 int index, int size, @Nullable String desc) {
299 // Carefully optimized for execution by hotspot (explanatory comment above)
300 if (index < 0 || index >= size) {
301 throw new IndexOutOfBoundsException(badElementIndex(index, size, desc));
302 }
303 return index;
304 }
305
306 private static String badElementIndex(int index, int size, String desc) {
307 if (index < 0) {
308 return format("%s (%s) must not be negative", desc, index);
309 } else if (size < 0) {
310 throw new IllegalArgumentException("negative size: " + size);
311 } else { // index >= size
312 return format("%s (%s) must be less than size (%s)", desc, index, size);
313 }
314 }
315
316 /**
317 * Ensures that {@code index} specifies a valid <i>position</i> in an array,
318 * list or string of size {@code size}. A position index may range from zero
319 * to {@code size}, inclusive.
320 *
321 * @param index a user-supplied index identifying a position in an array, list
322 * or string
323 * @param size the size of that array, list or string
324 * @return the value of {@code index}
325 * @throws IndexOutOfBoundsException if {@code index} is negative or is
326 * greater than {@code size}
327 * @throws IllegalArgumentException if {@code size} is negative
328 */
329 public static int checkPositionIndex(int index, int size) {
330 return checkPositionIndex(index, size, "index");
331 }
332
333 /**
334 * Ensures that {@code index} specifies a valid <i>position</i> in an array,
335 * list or string of size {@code size}. A position index may range from zero
336 * to {@code size}, inclusive.
337 *
338 * @param index a user-supplied index identifying a position in an array, list
339 * or string
340 * @param size the size of that array, list or string
341 * @param desc the text to use to describe this index in an error message
342 * @return the value of {@code index}
343 * @throws IndexOutOfBoundsException if {@code index} is negative or is
344 * greater than {@code size}
345 * @throws IllegalArgumentException if {@code size} is negative
346 */
347 public static int checkPositionIndex(
348 int index, int size, @Nullable String desc) {
349 // Carefully optimized for execution by hotspot (explanatory comment above)
350 if (index < 0 || index > size) {
351 throw new IndexOutOfBoundsException(badPositionIndex(index, size, desc));
352 }
353 return index;
354 }
355
356 private static String badPositionIndex(int index, int size, String desc) {
357 if (index < 0) {
358 return format("%s (%s) must not be negative", desc, index);
359 } else if (size < 0) {
360 throw new IllegalArgumentException("negative size: " + size);
361 } else { // index > size
362 return format("%s (%s) must not be greater than size (%s)",
363 desc, index, size);
364 }
365 }
366
367 /**
368 * Ensures that {@code start} and {@code end} specify a valid <i>positions</i>
369 * in an array, list or string of size {@code size}, and are in order. A
370 * position index may range from zero to {@code size}, inclusive.
371 *
372 * @param start a user-supplied index identifying a starting position in an
373 * array, list or string
374 * @param end a user-supplied index identifying a ending position in an array,
375 * list or string
376 * @param size the size of that array, list or string
377 * @throws IndexOutOfBoundsException if either index is negative or is
378 * greater than {@code size}, or if {@code end} is less than {@code start}
379 * @throws IllegalArgumentException if {@code size} is negative
380 */
381 public static void checkPositionIndexes(int start, int end, int size) {
382 // Carefully optimized for execution by hotspot (explanatory comment above)
383 if (start < 0 || end < start || end > size) {
384 throw new IndexOutOfBoundsException(badPositionIndexes(start, end, size));
385 }
386 }
387
388 private static String badPositionIndexes(int start, int end, int size) {
389 if (start < 0 || start > size) {
390 return badPositionIndex(start, size, "start index");
391 }
392 if (end < 0 || end > size) {
393 return badPositionIndex(end, size, "end index");
394 }
395 // end < start
396 return format("end index (%s) must not be less than start index (%s)",
397 end, start);
398 }
399
400 /**
401 * Substitutes each {@code %s} in {@code template} with an argument. These
402 * are matched by position - the first {@code %s} gets {@code args[0]}, etc.
403 * If there are more arguments than placeholders, the unmatched arguments will
404 * be appended to the end of the formatted message in square braces.
405 *
406 * @param template a non-null string containing 0 or more {@code %s}
407 * placeholders.
408 * @param args the arguments to be substituted into the message
409 * template. Arguments are converted to strings using
410 * {@link String#valueOf(Object)}. Arguments can be null.
411 */
412 @VisibleForTesting static String format(String template,
413 @Nullable Object... args) {
414 template = String.valueOf(template); // null -> "null"
415
416 // start substituting the arguments into the '%s' placeholders
417 StringBuilder builder = new StringBuilder(
418 template.length() + 16 * args.length);
419 int templateStart = 0;
420 int i = 0;
421 while (i < args.length) {
422 int placeholderStart = template.indexOf("%s", templateStart);
423 if (placeholderStart == -1) {
424 break;
425 }
426 builder.append(template.substring(templateStart, placeholderStart));
427 builder.append(args[i++]);
428 templateStart = placeholderStart + 2;
429 }
430 builder.append(template.substring(templateStart));
431
432 // if we run out of placeholders, append the extra args in square braces
433 if (i < args.length) {
434 builder.append(" [");
435 builder.append(args[i++]);
436 while (i < args.length) {
437 builder.append(", ");
438 builder.append(args[i++]);
439 }
440 builder.append(']');
441 }
442
443 return builder.toString();
444 }
445 }