1 /* 2 * Copyright (C) 2014 The Android Open Source Project 3 * Copyright (c) 1994, 2010, Oracle and/or its affiliates. All rights reserved. 4 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 5 * 6 * This code is free software; you can redistribute it and/or modify it 7 * under the terms of the GNU General Public License version 2 only, as 8 * published by the Free Software Foundation. Oracle designates this 9 * particular file as subject to the "Classpath" exception as provided 10 * by Oracle in the LICENSE file that accompanied this code. 11 * 12 * This code is distributed in the hope that it will be useful, but WITHOUT 13 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 14 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 15 * version 2 for more details (a copy is included in the LICENSE file that 16 * accompanied this code). 17 * 18 * You should have received a copy of the GNU General Public License version 19 * 2 along with this work; if not, write to the Free Software Foundation, 20 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 21 * 22 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 23 * or visit www.oracle.com if you need additional information or have any 24 * questions. 25 */ 26 27 package java.lang; 28 29 /** 30 * Class {@code Object} is the root of the class hierarchy. 31 * Every class has {@code Object} as a superclass. All objects, 32 * including arrays, implement the methods of this class. 33 * 34 * @author unascribed 35 * @see java.lang.Class 36 * @since JDK1.0 37 */ 38 public class Object { 39 40 private transient Class<?> shadow$_klass_; 41 private transient int shadow$_monitor_; 42 43 /** 44 * Returns the runtime class of this {@code Object}. The returned 45 * {@code Class} object is the object that is locked by {@code 46 * static synchronized} methods of the represented class. 47 * 48 * <p><b>The actual result type is {@code Class<? extends |X|>} 49 * where {@code |X|} is the erasure of the static type of the 50 * expression on which {@code getClass} is called.</b> For 51 * example, no cast is required in this code fragment:</p> 52 * 53 * <p> 54 * {@code Number n = 0; }<br> 55 * {@code Class<? extends Number> c = n.getClass(); } 56 * </p> 57 * 58 * @return The {@code Class} object that represents the runtime 59 * class of this object. 60 * @see Class Literals, section 15.8.2 of 61 * <cite>The Java™ Language Specification</cite>. 62 */ 63 public final Class<?> getClass() { 64 return shadow$_klass_; 65 } 66 67 /** 68 * Returns a hash code value for the object. This method is 69 * supported for the benefit of hash tables such as those provided by 70 * {@link java.util.HashMap}. 71 * <p> 72 * The general contract of {@code hashCode} is: 73 * <ul> 74 * <li>Whenever it is invoked on the same object more than once during 75 * an execution of a Java application, the {@code hashCode} method 76 * must consistently return the same integer, provided no information 77 * used in {@code equals} comparisons on the object is modified. 78 * This integer need not remain consistent from one execution of an 79 * application to another execution of the same application. 80 * <li>If two objects are equal according to the {@code equals(Object)} 81 * method, then calling the {@code hashCode} method on each of 82 * the two objects must produce the same integer result. 83 * <li>It is <em>not</em> required that if two objects are unequal 84 * according to the {@link java.lang.Object#equals(java.lang.Object)} 85 * method, then calling the {@code hashCode} method on each of the 86 * two objects must produce distinct integer results. However, the 87 * programmer should be aware that producing distinct integer results 88 * for unequal objects may improve the performance of hash tables. 89 * </ul> 90 * <p> 91 * As much as is reasonably practical, the hashCode method defined by 92 * class {@code Object} does return distinct integers for distinct 93 * objects. (This is typically implemented by converting the internal 94 * address of the object into an integer, but this implementation 95 * technique is not required by the 96 * Java<font size="-2"><sup>TM</sup></font> programming language.) 97 * 98 * @return a hash code value for this object. 99 * @see java.lang.Object#equals(java.lang.Object) 100 * @see java.lang.System#identityHashCode 101 */ 102 public int hashCode() { 103 int lockWord = shadow$_monitor_; 104 final int lockWordStateMask = 0xC0000000; // Top 2 bits. 105 final int lockWordStateHash = 0x80000000; // Top 2 bits are value 2 (kStateHash). 106 final int lockWordHashMask = 0x0FFFFFFF; // Low 28 bits. 107 if ((lockWord & lockWordStateMask) == lockWordStateHash) { 108 return lockWord & lockWordHashMask; 109 } 110 return System.identityHashCode(this); 111 } 112 113 /** 114 * Indicates whether some other object is "equal to" this one. 115 * <p> 116 * The {@code equals} method implements an equivalence relation 117 * on non-null object references: 118 * <ul> 119 * <li>It is <i>reflexive</i>: for any non-null reference value 120 * {@code x}, {@code x.equals(x)} should return 121 * {@code true}. 122 * <li>It is <i>symmetric</i>: for any non-null reference values 123 * {@code x} and {@code y}, {@code x.equals(y)} 124 * should return {@code true} if and only if 125 * {@code y.equals(x)} returns {@code true}. 126 * <li>It is <i>transitive</i>: for any non-null reference values 127 * {@code x}, {@code y}, and {@code z}, if 128 * {@code x.equals(y)} returns {@code true} and 129 * {@code y.equals(z)} returns {@code true}, then 130 * {@code x.equals(z)} should return {@code true}. 131 * <li>It is <i>consistent</i>: for any non-null reference values 132 * {@code x} and {@code y}, multiple invocations of 133 * {@code x.equals(y)} consistently return {@code true} 134 * or consistently return {@code false}, provided no 135 * information used in {@code equals} comparisons on the 136 * objects is modified. 137 * <li>For any non-null reference value {@code x}, 138 * {@code x.equals(null)} should return {@code false}. 139 * </ul> 140 * <p> 141 * The {@code equals} method for class {@code Object} implements 142 * the most discriminating possible equivalence relation on objects; 143 * that is, for any non-null reference values {@code x} and 144 * {@code y}, this method returns {@code true} if and only 145 * if {@code x} and {@code y} refer to the same object 146 * ({@code x == y} has the value {@code true}). 147 * <p> 148 * Note that it is generally necessary to override the {@code hashCode} 149 * method whenever this method is overridden, so as to maintain the 150 * general contract for the {@code hashCode} method, which states 151 * that equal objects must have equal hash codes. 152 * 153 * @param obj the reference object with which to compare. 154 * @return {@code true} if this object is the same as the obj 155 * argument; {@code false} otherwise. 156 * @see #hashCode() 157 * @see java.util.HashMap 158 */ 159 public boolean equals(Object obj) { 160 return (this == obj); 161 } 162 163 /** 164 * Creates and returns a copy of this object. The precise meaning 165 * of "copy" may depend on the class of the object. The general 166 * intent is that, for any object {@code x}, the expression: 167 * <blockquote> 168 * <pre> 169 * x.clone() != x</pre></blockquote> 170 * will be true, and that the expression: 171 * <blockquote> 172 * <pre> 173 * x.clone().getClass() == x.getClass()</pre></blockquote> 174 * will be {@code true}, but these are not absolute requirements. 175 * While it is typically the case that: 176 * <blockquote> 177 * <pre> 178 * x.clone().equals(x)</pre></blockquote> 179 * will be {@code true}, this is not an absolute requirement. 180 * <p> 181 * By convention, the returned object should be obtained by calling 182 * {@code super.clone}. If a class and all of its superclasses (except 183 * {@code Object}) obey this convention, it will be the case that 184 * {@code x.clone().getClass() == x.getClass()}. 185 * <p> 186 * By convention, the object returned by this method should be independent 187 * of this object (which is being cloned). To achieve this independence, 188 * it may be necessary to modify one or more fields of the object returned 189 * by {@code super.clone} before returning it. Typically, this means 190 * copying any mutable objects that comprise the internal "deep structure" 191 * of the object being cloned and replacing the references to these 192 * objects with references to the copies. If a class contains only 193 * primitive fields or references to immutable objects, then it is usually 194 * the case that no fields in the object returned by {@code super.clone} 195 * need to be modified. 196 * <p> 197 * The method {@code clone} for class {@code Object} performs a 198 * specific cloning operation. First, if the class of this object does 199 * not implement the interface {@code Cloneable}, then a 200 * {@code CloneNotSupportedException} is thrown. Note that all arrays 201 * are considered to implement the interface {@code Cloneable} and that 202 * the return type of the {@code clone} method of an array type {@code T[]} 203 * is {@code T[]} where T is any reference or primitive type. 204 * Otherwise, this method creates a new instance of the class of this 205 * object and initializes all its fields with exactly the contents of 206 * the corresponding fields of this object, as if by assignment; the 207 * contents of the fields are not themselves cloned. Thus, this method 208 * performs a "shallow copy" of this object, not a "deep copy" operation. 209 * <p> 210 * The class {@code Object} does not itself implement the interface 211 * {@code Cloneable}, so calling the {@code clone} method on an object 212 * whose class is {@code Object} will result in throwing an 213 * exception at run time. 214 * 215 * @return a clone of this instance. 216 * @exception CloneNotSupportedException if the object's class does not 217 * support the {@code Cloneable} interface. Subclasses 218 * that override the {@code clone} method can also 219 * throw this exception to indicate that an instance cannot 220 * be cloned. 221 * @see java.lang.Cloneable 222 */ 223 protected Object clone() throws CloneNotSupportedException { 224 if (!(this instanceof Cloneable)) { 225 throw new CloneNotSupportedException("Class " + getClass().getName() + 226 " doesn't implement Cloneable"); 227 } 228 229 return internalClone(); 230 } 231 232 /* 233 * Native helper method for cloning. 234 */ 235 private native Object internalClone(); 236 237 238 /** 239 * Returns a string representation of the object. In general, the 240 * {@code toString} method returns a string that 241 * "textually represents" this object. The result should 242 * be a concise but informative representation that is easy for a 243 * person to read. 244 * It is recommended that all subclasses override this method. 245 * <p> 246 * The {@code toString} method for class {@code Object} 247 * returns a string consisting of the name of the class of which the 248 * object is an instance, the at-sign character `{@code @}', and 249 * the unsigned hexadecimal representation of the hash code of the 250 * object. In other words, this method returns a string equal to the 251 * value of: 252 * <blockquote> 253 * <pre> 254 * getClass().getName() + '@' + Integer.toHexString(hashCode()) 255 * </pre></blockquote> 256 * 257 * @return a string representation of the object. 258 */ 259 public String toString() { 260 return getClass().getName() + "@" + Integer.toHexString(hashCode()); 261 } 262 263 /** 264 * Wakes up a single thread that is waiting on this object's 265 * monitor. If any threads are waiting on this object, one of them 266 * is chosen to be awakened. The choice is arbitrary and occurs at 267 * the discretion of the implementation. A thread waits on an object's 268 * monitor by calling one of the {@code wait} methods. 269 * <p> 270 * The awakened thread will not be able to proceed until the current 271 * thread relinquishes the lock on this object. The awakened thread will 272 * compete in the usual manner with any other threads that might be 273 * actively competing to synchronize on this object; for example, the 274 * awakened thread enjoys no reliable privilege or disadvantage in being 275 * the next thread to lock this object. 276 * <p> 277 * This method should only be called by a thread that is the owner 278 * of this object's monitor. A thread becomes the owner of the 279 * object's monitor in one of three ways: 280 * <ul> 281 * <li>By executing a synchronized instance method of that object. 282 * <li>By executing the body of a {@code synchronized} statement 283 * that synchronizes on the object. 284 * <li>For objects of type {@code Class,} by executing a 285 * synchronized static method of that class. 286 * </ul> 287 * <p> 288 * Only one thread at a time can own an object's monitor. 289 * 290 * @exception IllegalMonitorStateException if the current thread is not 291 * the owner of this object's monitor. 292 * @see java.lang.Object#notifyAll() 293 * @see java.lang.Object#wait() 294 */ 295 public final native void notify(); 296 297 /** 298 * Wakes up all threads that are waiting on this object's monitor. A 299 * thread waits on an object's monitor by calling one of the 300 * {@code wait} methods. 301 * <p> 302 * The awakened threads will not be able to proceed until the current 303 * thread relinquishes the lock on this object. The awakened threads 304 * will compete in the usual manner with any other threads that might 305 * be actively competing to synchronize on this object; for example, 306 * the awakened threads enjoy no reliable privilege or disadvantage in 307 * being the next thread to lock this object. 308 * <p> 309 * This method should only be called by a thread that is the owner 310 * of this object's monitor. See the {@code notify} method for a 311 * description of the ways in which a thread can become the owner of 312 * a monitor. 313 * 314 * @exception IllegalMonitorStateException if the current thread is not 315 * the owner of this object's monitor. 316 * @see java.lang.Object#notify() 317 * @see java.lang.Object#wait() 318 */ 319 public final native void notifyAll(); 320 321 /** 322 * Causes the current thread to wait until either another thread invokes the 323 * {@link java.lang.Object#notify()} method or the 324 * {@link java.lang.Object#notifyAll()} method for this object, or a 325 * specified amount of time has elapsed. 326 * <p> 327 * The current thread must own this object's monitor. 328 * <p> 329 * This method causes the current thread (call it <var>T</var>) to 330 * place itself in the wait set for this object and then to relinquish 331 * any and all synchronization claims on this object. Thread <var>T</var> 332 * becomes disabled for thread scheduling purposes and lies dormant 333 * until one of four things happens: 334 * <ul> 335 * <li>Some other thread invokes the {@code notify} method for this 336 * object and thread <var>T</var> happens to be arbitrarily chosen as 337 * the thread to be awakened. 338 * <li>Some other thread invokes the {@code notifyAll} method for this 339 * object. 340 * <li>Some other thread {@linkplain Thread#interrupt() interrupts} 341 * thread <var>T</var>. 342 * <li>The specified amount of real time has elapsed, more or less. If 343 * {@code timeout} is zero, however, then real time is not taken into 344 * consideration and the thread simply waits until notified. 345 * </ul> 346 * The thread <var>T</var> is then removed from the wait set for this 347 * object and re-enabled for thread scheduling. It then competes in the 348 * usual manner with other threads for the right to synchronize on the 349 * object; once it has gained control of the object, all its 350 * synchronization claims on the object are restored to the status quo 351 * ante - that is, to the situation as of the time that the {@code wait} 352 * method was invoked. Thread <var>T</var> then returns from the 353 * invocation of the {@code wait} method. Thus, on return from the 354 * {@code wait} method, the synchronization state of the object and of 355 * thread {@code T} is exactly as it was when the {@code wait} method 356 * was invoked. 357 * <p> 358 * A thread can also wake up without being notified, interrupted, or 359 * timing out, a so-called <i>spurious wakeup</i>. While this will rarely 360 * occur in practice, applications must guard against it by testing for 361 * the condition that should have caused the thread to be awakened, and 362 * continuing to wait if the condition is not satisfied. In other words, 363 * waits should always occur in loops, like this one: 364 * <pre> 365 * synchronized (obj) { 366 * while (<condition does not hold>) 367 * obj.wait(timeout); 368 * ... // Perform action appropriate to condition 369 * } 370 * </pre> 371 * (For more information on this topic, see Section 3.2.3 in Doug Lea's 372 * "Concurrent Programming in Java (Second Edition)" (Addison-Wesley, 373 * 2000), or Item 50 in Joshua Bloch's "Effective Java Programming 374 * Language Guide" (Addison-Wesley, 2001). 375 * 376 * <p>If the current thread is {@linkplain java.lang.Thread#interrupt() 377 * interrupted} by any thread before or while it is waiting, then an 378 * {@code InterruptedException} is thrown. This exception is not 379 * thrown until the lock status of this object has been restored as 380 * described above. 381 * 382 * <p> 383 * Note that the {@code wait} method, as it places the current thread 384 * into the wait set for this object, unlocks only this object; any 385 * other objects on which the current thread may be synchronized remain 386 * locked while the thread waits. 387 * <p> 388 * This method should only be called by a thread that is the owner 389 * of this object's monitor. See the {@code notify} method for a 390 * description of the ways in which a thread can become the owner of 391 * a monitor. 392 * 393 * @param millis the maximum time to wait in milliseconds. 394 * @exception IllegalArgumentException if the value of timeout is 395 * negative. 396 * @exception IllegalMonitorStateException if the current thread is not 397 * the owner of the object's monitor. 398 * @exception InterruptedException if any thread interrupted the 399 * current thread before or while the current thread 400 * was waiting for a notification. The <i>interrupted 401 * status</i> of the current thread is cleared when 402 * this exception is thrown. 403 * @see java.lang.Object#notify() 404 * @see java.lang.Object#notifyAll() 405 */ 406 public final void wait(long millis) throws InterruptedException { 407 wait(millis, 0); 408 } 409 410 /** 411 * Causes the current thread to wait until another thread invokes the 412 * {@link java.lang.Object#notify()} method or the 413 * {@link java.lang.Object#notifyAll()} method for this object, or 414 * some other thread interrupts the current thread, or a certain 415 * amount of real time has elapsed. 416 * <p> 417 * This method is similar to the {@code wait} method of one 418 * argument, but it allows finer control over the amount of time to 419 * wait for a notification before giving up. The amount of real time, 420 * measured in nanoseconds, is given by: 421 * <blockquote> 422 * <pre> 423 * 1000000*timeout+nanos</pre></blockquote> 424 * <p> 425 * In all other respects, this method does the same thing as the 426 * method {@link #wait(long)} of one argument. In particular, 427 * {@code wait(0, 0)} means the same thing as {@code wait(0)}. 428 * <p> 429 * The current thread must own this object's monitor. The thread 430 * releases ownership of this monitor and waits until either of the 431 * following two conditions has occurred: 432 * <ul> 433 * <li>Another thread notifies threads waiting on this object's monitor 434 * to wake up either through a call to the {@code notify} method 435 * or the {@code notifyAll} method. 436 * <li>The timeout period, specified by {@code timeout} 437 * milliseconds plus {@code nanos} nanoseconds arguments, has 438 * elapsed. 439 * </ul> 440 * <p> 441 * The thread then waits until it can re-obtain ownership of the 442 * monitor and resumes execution. 443 * <p> 444 * As in the one argument version, interrupts and spurious wakeups are 445 * possible, and this method should always be used in a loop: 446 * <pre> 447 * synchronized (obj) { 448 * while (<condition does not hold>) 449 * obj.wait(timeout, nanos); 450 * ... // Perform action appropriate to condition 451 * } 452 * </pre> 453 * This method should only be called by a thread that is the owner 454 * of this object's monitor. See the {@code notify} method for a 455 * description of the ways in which a thread can become the owner of 456 * a monitor. 457 * 458 * @param millis the maximum time to wait in milliseconds. 459 * @param nanos additional time, in nanoseconds range 460 * 0-999999. 461 * @exception IllegalArgumentException if the value of timeout is 462 * negative or the value of nanos is 463 * not in the range 0-999999. 464 * @exception IllegalMonitorStateException if the current thread is not 465 * the owner of this object's monitor. 466 * @exception InterruptedException if any thread interrupted the 467 * current thread before or while the current thread 468 * was waiting for a notification. The <i>interrupted 469 * status</i> of the current thread is cleared when 470 * this exception is thrown. 471 */ 472 public final native void wait(long millis, int nanos) throws InterruptedException; 473 474 /** 475 * Causes the current thread to wait until another thread invokes the 476 * {@link java.lang.Object#notify()} method or the 477 * {@link java.lang.Object#notifyAll()} method for this object. 478 * In other words, this method behaves exactly as if it simply 479 * performs the call {@code wait(0)}. 480 * <p> 481 * The current thread must own this object's monitor. The thread 482 * releases ownership of this monitor and waits until another thread 483 * notifies threads waiting on this object's monitor to wake up 484 * either through a call to the {@code notify} method or the 485 * {@code notifyAll} method. The thread then waits until it can 486 * re-obtain ownership of the monitor and resumes execution. 487 * <p> 488 * As in the one argument version, interrupts and spurious wakeups are 489 * possible, and this method should always be used in a loop: 490 * <pre> 491 * synchronized (obj) { 492 * while (<condition does not hold>) 493 * obj.wait(); 494 * ... // Perform action appropriate to condition 495 * } 496 * </pre> 497 * This method should only be called by a thread that is the owner 498 * of this object's monitor. See the {@code notify} method for a 499 * description of the ways in which a thread can become the owner of 500 * a monitor. 501 * 502 * @exception IllegalMonitorStateException if the current thread is not 503 * the owner of the object's monitor. 504 * @exception InterruptedException if any thread interrupted the 505 * current thread before or while the current thread 506 * was waiting for a notification. The <i>interrupted 507 * status</i> of the current thread is cleared when 508 * this exception is thrown. 509 * @see java.lang.Object#notify() 510 * @see java.lang.Object#notifyAll() 511 */ 512 public final native void wait() throws InterruptedException; 513 514 /** 515 * Called by the garbage collector on an object when garbage collection 516 * determines that there are no more references to the object. 517 * A subclass overrides the {@code finalize} method to dispose of 518 * system resources or to perform other cleanup. 519 * <p> 520 * The general contract of {@code finalize} is that it is invoked 521 * if and when the Java<font size="-2"><sup>TM</sup></font> virtual 522 * machine has determined that there is no longer any 523 * means by which this object can be accessed by any thread that has 524 * not yet died, except as a result of an action taken by the 525 * finalization of some other object or class which is ready to be 526 * finalized. The {@code finalize} method may take any action, including 527 * making this object available again to other threads; the usual purpose 528 * of {@code finalize}, however, is to perform cleanup actions before 529 * the object is irrevocably discarded. For example, the finalize method 530 * for an object that represents an input/output connection might perform 531 * explicit I/O transactions to break the connection before the object is 532 * permanently discarded. 533 * <p> 534 * The {@code finalize} method of class {@code Object} performs no 535 * special action; it simply returns normally. Subclasses of 536 * {@code Object} may override this definition. 537 * <p> 538 * The Java programming language does not guarantee which thread will 539 * invoke the {@code finalize} method for any given object. It is 540 * guaranteed, however, that the thread that invokes finalize will not 541 * be holding any user-visible synchronization locks when finalize is 542 * invoked. If an uncaught exception is thrown by the finalize method, 543 * the exception is ignored and finalization of that object terminates. 544 * <p> 545 * After the {@code finalize} method has been invoked for an object, no 546 * further action is taken until the Java virtual machine has again 547 * determined that there is no longer any means by which this object can 548 * be accessed by any thread that has not yet died, including possible 549 * actions by other objects or classes which are ready to be finalized, 550 * at which point the object may be discarded. 551 * <p> 552 * The {@code finalize} method is never invoked more than once by a Java 553 * virtual machine for any given object. 554 * <p> 555 * Any exception thrown by the {@code finalize} method causes 556 * the finalization of this object to be halted, but is otherwise 557 * ignored. 558 * 559 * @throws Throwable the {@code Exception} raised by this method 560 */ 561 protected void finalize() throws Throwable { } 562 } 563