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 * <p>See the Guava User Guide on <a href=
057 * "http://code.google.com/p/guava-libraries/wiki/PreconditionsExplained">
058 * using {@code Preconditions}</a>.
059 *
060 * @author Kevin Bourrillion
061 * @since 2.0 (imported from Google Collections Library)
062 */
063 @GwtCompatible
064 public final class Preconditions {
065 private Preconditions() {}
066
067 /**
068 * Ensures the truth of an expression involving one or more parameters to the
069 * calling method.
070 *
071 * @param expression a boolean expression
072 * @throws IllegalArgumentException if {@code expression} is false
073 */
074 public static void checkArgument(boolean expression) {
075 if (!expression) {
076 throw new IllegalArgumentException();
077 }
078 }
079
080 /**
081 * Ensures the truth of an expression involving one or more parameters to the
082 * calling method.
083 *
084 * @param expression a boolean expression
085 * @param errorMessage the exception message to use if the check fails; will
086 * be converted to a string using {@link String#valueOf(Object)}
087 * @throws IllegalArgumentException if {@code expression} is false
088 */
089 public static void checkArgument(
090 boolean expression, @Nullable Object errorMessage) {
091 if (!expression) {
092 throw new IllegalArgumentException(String.valueOf(errorMessage));
093 }
094 }
095
096 /**
097 * Ensures the truth of an expression involving one or more parameters to the
098 * calling method.
099 *
100 * @param expression a boolean expression
101 * @param errorMessageTemplate a template for the exception message should the
102 * check fail. The message is formed by replacing each {@code %s}
103 * placeholder in the template with an argument. These are matched by
104 * position - the first {@code %s} gets {@code errorMessageArgs[0]}, etc.
105 * Unmatched arguments will be appended to the formatted message in square
106 * braces. Unmatched placeholders will be left as-is.
107 * @param errorMessageArgs the arguments to be substituted into the message
108 * template. Arguments are converted to strings using
109 * {@link String#valueOf(Object)}.
110 * @throws IllegalArgumentException if {@code expression} is false
111 * @throws NullPointerException if the check fails and either {@code
112 * errorMessageTemplate} or {@code errorMessageArgs} is null (don't let
113 * this happen)
114 */
115 public static void checkArgument(boolean expression,
116 @Nullable String errorMessageTemplate,
117 @Nullable Object... errorMessageArgs) {
118 if (!expression) {
119 throw new IllegalArgumentException(
120 format(errorMessageTemplate, errorMessageArgs));
121 }
122 }
123
124 /**
125 * Ensures the truth of an expression involving the state of the calling
126 * instance, but not involving any parameters to the calling method.
127 *
128 * @param expression a boolean expression
129 * @throws IllegalStateException if {@code expression} is false
130 */
131 public static void checkState(boolean expression) {
132 if (!expression) {
133 throw new IllegalStateException();
134 }
135 }
136
137 /**
138 * Ensures the truth of an expression involving the state of the calling
139 * instance, but not involving any parameters to the calling method.
140 *
141 * @param expression a boolean expression
142 * @param errorMessage the exception message to use if the check fails; will
143 * be converted to a string using {@link String#valueOf(Object)}
144 * @throws IllegalStateException if {@code expression} is false
145 */
146 public static void checkState(
147 boolean expression, @Nullable Object errorMessage) {
148 if (!expression) {
149 throw new IllegalStateException(String.valueOf(errorMessage));
150 }
151 }
152
153 /**
154 * Ensures the truth of an expression involving the state of the calling
155 * instance, but not involving any parameters to the calling method.
156 *
157 * @param expression a boolean expression
158 * @param errorMessageTemplate a template for the exception message should the
159 * check fail. The message is formed by replacing each {@code %s}
160 * placeholder in the template with an argument. These are matched by
161 * position - the first {@code %s} gets {@code errorMessageArgs[0]}, etc.
162 * Unmatched arguments will be appended to the formatted message in square
163 * braces. Unmatched placeholders will be left as-is.
164 * @param errorMessageArgs the arguments to be substituted into the message
165 * template. Arguments are converted to strings using
166 * {@link String#valueOf(Object)}.
167 * @throws IllegalStateException if {@code expression} is false
168 * @throws NullPointerException if the check fails and either {@code
169 * errorMessageTemplate} or {@code errorMessageArgs} is null (don't let
170 * this happen)
171 */
172 public static void checkState(boolean expression,
173 @Nullable String errorMessageTemplate,
174 @Nullable Object... errorMessageArgs) {
175 if (!expression) {
176 throw new IllegalStateException(
177 format(errorMessageTemplate, errorMessageArgs));
178 }
179 }
180
181 /**
182 * Ensures that an object reference passed as a parameter to the calling
183 * method is not null.
184 *
185 * @param reference an object reference
186 * @return the non-null reference that was validated
187 * @throws NullPointerException if {@code reference} is null
188 */
189 public static <T> T checkNotNull(T reference) {
190 if (reference == null) {
191 throw new NullPointerException();
192 }
193 return reference;
194 }
195
196 /**
197 * Ensures that an object reference passed as a parameter to the calling
198 * method is not null.
199 *
200 * @param reference an object reference
201 * @param errorMessage the exception message to use if the check fails; will
202 * be converted to a string using {@link String#valueOf(Object)}
203 * @return the non-null reference that was validated
204 * @throws NullPointerException if {@code reference} is null
205 */
206 public static <T> T checkNotNull(T reference, @Nullable Object errorMessage) {
207 if (reference == null) {
208 throw new NullPointerException(String.valueOf(errorMessage));
209 }
210 return reference;
211 }
212
213 /**
214 * Ensures that an object reference passed as a parameter to the calling
215 * method is not null.
216 *
217 * @param reference an object reference
218 * @param errorMessageTemplate a template for the exception message should the
219 * check fail. The message is formed by replacing each {@code %s}
220 * placeholder in the template with an argument. These are matched by
221 * position - the first {@code %s} gets {@code errorMessageArgs[0]}, etc.
222 * Unmatched arguments will be appended to the formatted message in square
223 * braces. Unmatched placeholders will be left as-is.
224 * @param errorMessageArgs the arguments to be substituted into the message
225 * template. Arguments are converted to strings using
226 * {@link String#valueOf(Object)}.
227 * @return the non-null reference that was validated
228 * @throws NullPointerException if {@code reference} is null
229 */
230 public static <T> T checkNotNull(T reference,
231 @Nullable String errorMessageTemplate,
232 @Nullable Object... errorMessageArgs) {
233 if (reference == null) {
234 // If either of these parameters is null, the right thing happens anyway
235 throw new NullPointerException(
236 format(errorMessageTemplate, errorMessageArgs));
237 }
238 return reference;
239 }
240
241 /*
242 * All recent hotspots (as of 2009) *really* like to have the natural code
243 *
244 * if (guardExpression) {
245 * throw new BadException(messageExpression);
246 * }
247 *
248 * refactored so that messageExpression is moved to a separate
249 * String-returning method.
250 *
251 * if (guardExpression) {
252 * throw new BadException(badMsg(...));
253 * }
254 *
255 * The alternative natural refactorings into void or Exception-returning
256 * methods are much slower. This is a big deal - we're talking factors of
257 * 2-8 in microbenchmarks, not just 10-20%. (This is a hotspot optimizer
258 * bug, which should be fixed, but that's a separate, big project).
259 *
260 * The coding pattern above is heavily used in java.util, e.g. in ArrayList.
261 * There is a RangeCheckMicroBenchmark in the JDK that was used to test this.
262 *
263 * But the methods in this class want to throw different exceptions,
264 * depending on the args, so it appears that this pattern is not directly
265 * applicable. But we can use the ridiculous, devious trick of throwing an
266 * exception in the middle of the construction of another exception.
267 * Hotspot is fine with that.
268 */
269
270 /**
271 * Ensures that {@code index} specifies a valid <i>element</i> in an array,
272 * list or string of size {@code size}. An element index may range from zero,
273 * inclusive, to {@code size}, exclusive.
274 *
275 * @param index a user-supplied index identifying an element of an array, list
276 * or string
277 * @param size the size of that array, list or string
278 * @return the value of {@code index}
279 * @throws IndexOutOfBoundsException if {@code index} is negative or is not
280 * less than {@code size}
281 * @throws IllegalArgumentException if {@code size} is negative
282 */
283 public static int checkElementIndex(int index, int size) {
284 return checkElementIndex(index, size, "index");
285 }
286
287 /**
288 * Ensures that {@code index} specifies a valid <i>element</i> in an array,
289 * list or string of size {@code size}. An element index may range from zero,
290 * inclusive, to {@code size}, exclusive.
291 *
292 * @param index a user-supplied index identifying an element of an array, list
293 * or string
294 * @param size the size of that array, list or string
295 * @param desc the text to use to describe this index in an error message
296 * @return the value of {@code index}
297 * @throws IndexOutOfBoundsException if {@code index} is negative or is not
298 * less than {@code size}
299 * @throws IllegalArgumentException if {@code size} is negative
300 */
301 public static int checkElementIndex(
302 int index, int size, @Nullable String desc) {
303 // Carefully optimized for execution by hotspot (explanatory comment above)
304 if (index < 0 || index >= size) {
305 throw new IndexOutOfBoundsException(badElementIndex(index, size, desc));
306 }
307 return index;
308 }
309
310 private static String badElementIndex(int index, int size, String desc) {
311 if (index < 0) {
312 return format("%s (%s) must not be negative", desc, index);
313 } else if (size < 0) {
314 throw new IllegalArgumentException("negative size: " + size);
315 } else { // index >= size
316 return format("%s (%s) must be less than size (%s)", desc, index, size);
317 }
318 }
319
320 /**
321 * Ensures that {@code index} specifies a valid <i>position</i> in an array,
322 * list or string of size {@code size}. A position index may range from zero
323 * to {@code size}, inclusive.
324 *
325 * @param index a user-supplied index identifying a position in an array, list
326 * or string
327 * @param size the size of that array, list or string
328 * @return the value of {@code index}
329 * @throws IndexOutOfBoundsException if {@code index} is negative or is
330 * greater than {@code size}
331 * @throws IllegalArgumentException if {@code size} is negative
332 */
333 public static int checkPositionIndex(int index, int size) {
334 return checkPositionIndex(index, size, "index");
335 }
336
337 /**
338 * Ensures that {@code index} specifies a valid <i>position</i> in an array,
339 * list or string of size {@code size}. A position index may range from zero
340 * to {@code size}, inclusive.
341 *
342 * @param index a user-supplied index identifying a position in an array, list
343 * or string
344 * @param size the size of that array, list or string
345 * @param desc the text to use to describe this index in an error message
346 * @return the value of {@code index}
347 * @throws IndexOutOfBoundsException if {@code index} is negative or is
348 * greater than {@code size}
349 * @throws IllegalArgumentException if {@code size} is negative
350 */
351 public static int checkPositionIndex(
352 int index, int size, @Nullable String desc) {
353 // Carefully optimized for execution by hotspot (explanatory comment above)
354 if (index < 0 || index > size) {
355 throw new IndexOutOfBoundsException(badPositionIndex(index, size, desc));
356 }
357 return index;
358 }
359
360 private static String badPositionIndex(int index, int size, String desc) {
361 if (index < 0) {
362 return format("%s (%s) must not be negative", desc, index);
363 } else if (size < 0) {
364 throw new IllegalArgumentException("negative size: " + size);
365 } else { // index > size
366 return format("%s (%s) must not be greater than size (%s)",
367 desc, index, size);
368 }
369 }
370
371 /**
372 * Ensures that {@code start} and {@code end} specify a valid <i>positions</i>
373 * in an array, list or string of size {@code size}, and are in order. A
374 * position index may range from zero to {@code size}, inclusive.
375 *
376 * @param start a user-supplied index identifying a starting position in an
377 * array, list or string
378 * @param end a user-supplied index identifying a ending position in an array,
379 * list or string
380 * @param size the size of that array, list or string
381 * @throws IndexOutOfBoundsException if either index is negative or is
382 * greater than {@code size}, or if {@code end} is less than {@code start}
383 * @throws IllegalArgumentException if {@code size} is negative
384 */
385 public static void checkPositionIndexes(int start, int end, int size) {
386 // Carefully optimized for execution by hotspot (explanatory comment above)
387 if (start < 0 || end < start || end > size) {
388 throw new IndexOutOfBoundsException(badPositionIndexes(start, end, size));
389 }
390 }
391
392 private static String badPositionIndexes(int start, int end, int size) {
393 if (start < 0 || start > size) {
394 return badPositionIndex(start, size, "start index");
395 }
396 if (end < 0 || end > size) {
397 return badPositionIndex(end, size, "end index");
398 }
399 // end < start
400 return format("end index (%s) must not be less than start index (%s)",
401 end, start);
402 }
403
404 /**
405 * Substitutes each {@code %s} in {@code template} with an argument. These
406 * are matched by position - the first {@code %s} gets {@code args[0]}, etc.
407 * If there are more arguments than placeholders, the unmatched arguments will
408 * be appended to the end of the formatted message in square braces.
409 *
410 * @param template a non-null string containing 0 or more {@code %s}
411 * placeholders.
412 * @param args the arguments to be substituted into the message
413 * template. Arguments are converted to strings using
414 * {@link String#valueOf(Object)}. Arguments can be null.
415 */
416 @VisibleForTesting static String format(String template,
417 @Nullable Object... args) {
418 template = String.valueOf(template); // null -> "null"
419
420 // start substituting the arguments into the '%s' placeholders
421 StringBuilder builder = new StringBuilder(
422 template.length() + 16 * args.length);
423 int templateStart = 0;
424 int i = 0;
425 while (i < args.length) {
426 int placeholderStart = template.indexOf("%s", templateStart);
427 if (placeholderStart == -1) {
428 break;
429 }
430 builder.append(template.substring(templateStart, placeholderStart));
431 builder.append(args[i++]);
432 templateStart = placeholderStart + 2;
433 }
434 builder.append(template.substring(templateStart));
435
436 // if we run out of placeholders, append the extra args in square braces
437 if (i < args.length) {
438 builder.append(" [");
439 builder.append(args[i++]);
440 while (i < args.length) {
441 builder.append(", ");
442 builder.append(args[i++]);
443 }
444 builder.append(']');
445 }
446
447 return builder.toString();
448 }
449 }