/*
 * Copyright (c) 1994, 2018, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation. Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package java.lang;

import jdk.internal.HotSpotIntrinsicCandidate;

/**
 * Class {@code Object} is the root of the class hierarchy.
 * Every class has {@code Object} as a superclass. All objects,
 * including arrays, implement the methods of this class.
 *
 * @author unascribed
 * @see java.lang.Class
 * @since 1.0
 */
public class Object {

 private static native void registerNatives();
 static {
 registerNatives();
 }

 /**
 * Constructs a new object.
 */
 @HotSpotIntrinsicCandidate
 public Object() {}

 /**
 * Returns the runtime class of this {@code Object}. The returned
 * {@code Class} object is the object that is locked by {@code
 * static synchronized} methods of the represented class.
 *
 * <p><b>The actual result type is {@code Class<? extends |X|>}
 * where {@code |X|} is the erasure of the static type of the
 * expression on which {@code getClass} is called.</b> For
 * example, no cast is required in this code fragment:</p>
 *
 * <p>
 * {@code Number n = 0; }<br>
 * {@code Class<? extends Number> c = n.getClass(); }
 * </p>
 *
 * @return The {@code Class} object that represents the runtime
 * class of this object.
 * @jls 15.8.2 Class Literals
 */
 @HotSpotIntrinsicCandidate
 public final native Class<?> getClass();

 /**
 * Returns a hash code value for the object. This method is
 * supported for the benefit of hash tables such as those provided by
 * {@link java.util.HashMap}.
 * <p>
 * The general contract of {@code hashCode} is:
 * <ul>
 * <li>Whenever it is invoked on the same object more than once during
 * an execution of a Java application, the {@code hashCode} method
 * must consistently return the same integer, provided no information
 * used in {@code equals} comparisons on the object is modified.
 * This integer need not remain consistent from one execution of an
 * application to another execution of the same application.
 * <li>If two objects are equal according to the {@code equals(Object)}
 * method, then calling the {@code hashCode} method on each of
 * the two objects must produce the same integer result.
 * <li>It is <em>not</em> required that if two objects are unequal
 * according to the {@link java.lang.Object#equals(java.lang.Object)}
 * method, then calling the {@code hashCode} method on each of the
 * two objects must produce distinct integer results. However, the
 * programmer should be aware that producing distinct integer results
 * for unequal objects may improve the performance of hash tables.
 * </ul>
 *
 * @implSpec
 * As far as is reasonably practical, the {@code hashCode} method defined
 * by class {@code Object} returns distinct integers for distinct objects.
 *
 * @return a hash code value for this object.
 * @see java.lang.Object#equals(java.lang.Object)
 * @see java.lang.System#identityHashCode
 */
 @HotSpotIntrinsicCandidate
 public native int hashCode();

 /**
 * Indicates whether some other object is "equal to" this one.
 * <p>
 * The {@code equals} method implements an equivalence relation
 * on non-null object references:
 * <ul>
 * <li>It is <i>reflexive</i>: for any non-null reference value
 * {@code x}, {@code x.equals(x)} should return
 * {@code true}.
 * <li>It is <i>symmetric</i>: for any non-null reference values
 * {@code x} and {@code y}, {@code x.equals(y)}
 * should return {@code true} if and only if
 * {@code y.equals(x)} returns {@code true}.
 * <li>It is <i>transitive</i>: for any non-null reference values
 * {@code x}, {@code y}, and {@code z}, if
 * {@code x.equals(y)} returns {@code true} and
 * {@code y.equals(z)} returns {@code true}, then
 * {@code x.equals(z)} should return {@code true}.
 * <li>It is <i>consistent</i>: for any non-null reference values
 * {@code x} and {@code y}, multiple invocations of
 * {@code x.equals(y)} consistently return {@code true}
 * or consistently return {@code false}, provided no
 * information used in {@code equals} comparisons on the
 * objects is modified.
 * <li>For any non-null reference value {@code x},
 * {@code x.equals(null)} should return {@code false}.
 * </ul>
 * <p>
 * The {@code equals} method for class {@code Object} implements
 * the most discriminating possible equivalence relation on objects;
 * that is, for any non-null reference values {@code x} and
 * {@code y}, this method returns {@code true} if and only
 * if {@code x} and {@code y} refer to the same object
 * ({@code x == y} has the value {@code true}).
 * <p>
 * Note that it is generally necessary to override the {@code hashCode}
 * method whenever this method is overridden, so as to maintain the
 * general contract for the {@code hashCode} method, which states
 * that equal objects must have equal hash codes.
 *
 * @param obj the reference object with which to compare.
 * @return {@code true} if this object is the same as the obj
 * argument; {@code false} otherwise.
 * @see #hashCode()
 * @see java.util.HashMap
 */
 public boolean equals(Object obj) {
 return (this == obj);
 }

 /**
 * Creates and returns a copy of this object. The precise meaning
 * of "copy" may depend on the class of the object. The general
 * intent is that, for any object {@code x}, the expression:
 * <blockquote>
 * <pre>
 * x.clone() != x</pre></blockquote>
 * will be true, and that the expression:
 * <blockquote>
 * <pre>
 * x.clone().getClass() == x.getClass()</pre></blockquote>
 * will be {@code true}, but these are not absolute requirements.
 * While it is typically the case that:
 * <blockquote>
 * <pre>
 * x.clone().equals(x)</pre></blockquote>
 * will be {@code true}, this is not an absolute requirement.
 * <p>
 * By convention, the returned object should be obtained by calling
 * {@code super.clone}. If a class and all of its superclasses (except
 * {@code Object}) obey this convention, it will be the case that
 * {@code x.clone().getClass() == x.getClass()}.
 * <p>
 * By convention, the object returned by this method should be independent
 * of this object (which is being cloned). To achieve this independence,
 * it may be necessary to modify one or more fields of the object returned
 * by {@code super.clone} before returning it. Typically, this means
 * copying any mutable objects that comprise the internal "deep structure"
 * of the object being cloned and replacing the references to these
 * objects with references to the copies. If a class contains only
 * primitive fields or references to immutable objects, then it is usually
 * the case that no fields in the object returned by {@code super.clone}
 * need to be modified.
 * <p>
 * The method {@code clone} for class {@code Object} performs a
 * specific cloning operation. First, if the class of this object does
 * not implement the interface {@code Cloneable}, then a
 * {@code CloneNotSupportedException} is thrown. Note that all arrays
 * are considered to implement the interface {@code Cloneable} and that
 * the return type of the {@code clone} method of an array type {@code T[]}
 * is {@code T[]} where T is any reference or primitive type.
 * Otherwise, this method creates a new instance of the class of this
 * object and initializes all its fields with exactly the contents of
 * the corresponding fields of this object, as if by assignment; the
 * contents of the fields are not themselves cloned. Thus, this method
 * performs a "shallow copy" of this object, not a "deep copy" operation.
 * <p>
 * The class {@code Object} does not itself implement the interface
 * {@code Cloneable}, so calling the {@code clone} method on an object
 * whose class is {@code Object} will result in throwing an
 * exception at run time.
 *
 * @return a clone of this instance.
 * @throws CloneNotSupportedException if the object's class does not
 * support the {@code Cloneable} interface. Subclasses
 * that override the {@code clone} method can also
 * throw this exception to indicate that an instance cannot
 * be cloned.
 * @see java.lang.Cloneable
 */
 @HotSpotIntrinsicCandidate
 protected native Object clone() throws CloneNotSupportedException;

 /**
 * Returns a string representation of the object. In general, the
 * {@code toString} method returns a string that
 * "textually represents" this object. The result should
 * be a concise but informative representation that is easy for a
 * person to read.
 * It is recommended that all subclasses override this method.
 * <p>
 * The {@code toString} method for class {@code Object}
 * returns a string consisting of the name of the class of which the
 * object is an instance, the at-sign character `{@code @}', and
 * the unsigned hexadecimal representation of the hash code of the
 * object. In other words, this method returns a string equal to the
 * value of:
 * <blockquote>
 * <pre>
 * getClass().getName() + '@' + Integer.toHexString(hashCode())
 * </pre></blockquote>
 *
 * @return a string representation of the object.
 */
 public String toString() {
 return getClass().getName() + "@" + Integer.toHexString(hashCode());
 }

 /**
 * Wakes up a single thread that is waiting on this object's
 * monitor. If any threads are waiting on this object, one of them
 * is chosen to be awakened. The choice is arbitrary and occurs at
 * the discretion of the implementation. A thread waits on an object's
 * monitor by calling one of the {@code wait} methods.
 * <p>
 * The awakened thread will not be able to proceed until the current
 * thread relinquishes the lock on this object. The awakened thread will
 * compete in the usual manner with any other threads that might be
 * actively competing to synchronize on this object; for example, the
 * awakened thread enjoys no reliable privilege or disadvantage in being
 * the next thread to lock this object.
 * <p>
 * This method should only be called by a thread that is the owner
 * of this object's monitor. A thread becomes the owner of the
 * object's monitor in one of three ways:
 * <ul>
 * <li>By executing a synchronized instance method of that object.
 * <li>By executing the body of a {@code synchronized} statement
 * that synchronizes on the object.
 * <li>For objects of type {@code Class,} by executing a
 * synchronized static method of that class.
 * </ul>
 * <p>
 * Only one thread at a time can own an object's monitor.
 *
 * @throws IllegalMonitorStateException if the current thread is not
 * the owner of this object's monitor.
 * @see java.lang.Object#notifyAll()
 * @see java.lang.Object#wait()
 */
 @HotSpotIntrinsicCandidate
 public final native void notify();

 /**
 * Wakes up all threads that are waiting on this object's monitor. A
 * thread waits on an object's monitor by calling one of the
 * {@code wait} methods.
 * <p>
 * The awakened threads will not be able to proceed until the current
 * thread relinquishes the lock on this object. The awakened threads
 * will compete in the usual manner with any other threads that might
 * be actively competing to synchronize on this object; for example,
 * the awakened threads enjoy no reliable privilege or disadvantage in
 * being the next thread to lock this object.
 * <p>
 * This method should only be called by a thread that is the owner
 * of this object's monitor. See the {@code notify} method for a
 * description of the ways in which a thread can become the owner of
 * a monitor.
 *
 * @throws IllegalMonitorStateException if the current thread is not
 * the owner of this object's monitor.
 * @see java.lang.Object#notify()
 * @see java.lang.Object#wait()
 */
 @HotSpotIntrinsicCandidate
 public final native void notifyAll();

 /**
 * Causes the current thread to wait until it is awakened, typically
 * by being <em>notified</em> or <em>interrupted</em>.
 * <p>
 * In all respects, this method behaves as if {@code wait(0L, 0)}
 * had been called. See the specification of the {@link #wait(long, int)} method
 * for details.
 *
 * @throws IllegalMonitorStateException if the current thread is not
 * the owner of the object's monitor
 * @throws InterruptedException if any thread interrupted the current thread before or
 * while the current thread was waiting. The <em>interrupted status</em> of the
 * current thread is cleared when this exception is thrown.
 * @see #notify()
 * @see #notifyAll()
 * @see #wait(long)
 * @see #wait(long, int)
 */
 public final void wait() throws InterruptedException {
 wait(0L);
 }

 /**
 * Causes the current thread to wait until it is awakened, typically
 * by being <em>notified</em> or <em>interrupted</em>, or until a
 * certain amount of real time has elapsed.
 * <p>
 * In all respects, this method behaves as if {@code wait(timeoutMillis, 0)}
 * had been called. See the specification of the {@link #wait(long, int)} method
 * for details.
 *
 * @param timeoutMillis the maximum time to wait, in milliseconds
 * @throws IllegalArgumentException if {@code timeoutMillis} is negative
 * @throws IllegalMonitorStateException if the current thread is not
 * the owner of the object's monitor
 * @throws InterruptedException if any thread interrupted the current thread before or
 * while the current thread was waiting. The <em>interrupted status</em> of the
 * current thread is cleared when this exception is thrown.
 * @see #notify()
 * @see #notifyAll()
 * @see #wait()
 * @see #wait(long, int)
 */
 public final native void wait(long timeoutMillis) throws InterruptedException;

 /**
 * Causes the current thread to wait until it is awakened, typically
 * by being <em>notified</em> or <em>interrupted</em>, or until a
 * certain amount of real time has elapsed.
 * <p>
 * The current thread must own this object's monitor lock. See the
 * {@link #notify notify} method for a description of the ways in which
 * a thread can become the owner of a monitor lock.
 * <p>
 * This method causes the current thread (referred to here as <var>T</var>) to
 * place itself in the wait set for this object and then to relinquish any
 * and all synchronization claims on this object. Note that only the locks
 * on this object are relinquished; any other objects on which the current
 * thread may be synchronized remain locked while the thread waits.
 * <p>
 * Thread <var>T</var> then becomes disabled for thread scheduling purposes
 * and lies dormant until one of the following occurs:
 * <ul>
 * <li>Some other thread invokes the {@code notify} method for this
 * object and thread <var>T</var> happens to be arbitrarily chosen as
 * the thread to be awakened.
 * <li>Some other thread invokes the {@code notifyAll} method for this
 * object.
 * <li>Some other thread {@linkplain Thread#interrupt() interrupts}
 * thread <var>T</var>.
 * <li>The specified amount of real time has elapsed, more or less.
 * The amount of real time, in nanoseconds, is given by the expression
 * {@code 1000000 * timeoutMillis + nanos}. If {@code timeoutMillis} and {@code nanos}
 * are both zero, then real time is not taken into consideration and the
 * thread waits until awakened by one of the other causes.
 * <li>Thread <var>T</var> is awakened spuriously. (See below.)
 * </ul>
 * <p>
 * The thread <var>T</var> is then removed from the wait set for this
 * object and re-enabled for thread scheduling. It competes in the
 * usual manner with other threads for the right to synchronize on the
 * object; once it has regained control of the object, all its
 * synchronization claims on the object are restored to the status quo
 * ante - that is, to the situation as of the time that the {@code wait}
 * method was invoked. Thread <var>T</var> then returns from the
 * invocation of the {@code wait} method. Thus, on return from the
 * {@code wait} method, the synchronization state of the object and of
 * thread {@code T} is exactly as it was when the {@code wait} method
 * was invoked.
 * <p>
 * A thread can wake up without being notified, interrupted, or timing out, a
 * so-called <em>spurious wakeup</em>. While this will rarely occur in practice,
 * applications must guard against it by testing for the condition that should
 * have caused the thread to be awakened, and continuing to wait if the condition
 * is not satisfied. See the example below.
 * <p>
 * For more information on this topic, see section 14.2,
 * "Condition Queues," in Brian Goetz and others' <em>Java Concurrency
 * in Practice</em> (Addison-Wesley, 2006) or Item 69 in Joshua
 * Bloch's <em>Effective Java, Second Edition</em> (Addison-Wesley,
 * 2008).
 * <p>
 * If the current thread is {@linkplain java.lang.Thread#interrupt() interrupted}
 * by any thread before or while it is waiting, then an {@code InterruptedException}
 * is thrown. The <em>interrupted status</em> of the current thread is cleared when
 * this exception is thrown. This exception is not thrown until the lock status of
 * this object has been restored as described above.
 *
 * @apiNote
 * The recommended approach to waiting is to check the condition being awaited in
 * a {@code while} loop around the call to {@code wait}, as shown in the example
 * below. Among other things, this approach avoids problems that can be caused
 * by spurious wakeups.
 *
 * <pre>{@code
 * synchronized (obj) {
 * while (<condition does not hold> and <timeout not exceeded>) {
 * long timeoutMillis = ... ; // recompute timeout values
 * int nanos = ... ;
 * obj.wait(timeoutMillis, nanos);
 * }
 * ... // Perform action appropriate to condition or timeout
 * }
 * }</pre>
 *
 * @param timeoutMillis the maximum time to wait, in milliseconds
 * @param nanos additional time, in nanoseconds, in the range range 0-999999 inclusive
 * @throws IllegalArgumentException if {@code timeoutMillis} is negative,
 * or if the value of {@code nanos} is out of range
 * @throws IllegalMonitorStateException if the current thread is not
 * the owner of the object's monitor
 * @throws InterruptedException if any thread interrupted the current thread before or
 * while the current thread was waiting. The <em>interrupted status</em> of the
 * current thread is cleared when this exception is thrown.
 * @see #notify()
 * @see #notifyAll()
 * @see #wait()
 * @see #wait(long)
 */
 public final void wait(long timeoutMillis, int nanos) throws InterruptedException {
 if (timeoutMillis < 0) {
 throw new IllegalArgumentException("timeoutMillis value is negative");
 }

 if (nanos < 0 || nanos > 999999) {
 throw new IllegalArgumentException(
 "nanosecond timeout value out of range");
 }

 if (nanos > 0 && timeoutMillis < Long.MAX_VALUE) {
 timeoutMillis++;
 }

 wait(timeoutMillis);
 }

 /**
 * Called by the garbage collector on an object when garbage collection
 * determines that there are no more references to the object.
 * A subclass overrides the {@code finalize} method to dispose of
 * system resources or to perform other cleanup.
 * <p>
 * The general contract of {@code finalize} is that it is invoked
 * if and when the Java&trade; virtual
 * machine has determined that there is no longer any
 * means by which this object can be accessed by any thread that has
 * not yet died, except as a result of an action taken by the
 * finalization of some other object or class which is ready to be
 * finalized. The {@code finalize} method may take any action, including
 * making this object available again to other threads; the usual purpose
 * of {@code finalize}, however, is to perform cleanup actions before
 * the object is irrevocably discarded. For example, the finalize method
 * for an object that represents an input/output connection might perform
 * explicit I/O transactions to break the connection before the object is
 * permanently discarded.
 * <p>
 * The {@code finalize} method of class {@code Object} performs no
 * special action; it simply returns normally. Subclasses of
 * {@code Object} may override this definition.
 * <p>
 * The Java programming language does not guarantee which thread will
 * invoke the {@code finalize} method for any given object. It is
 * guaranteed, however, that the thread that invokes finalize will not
 * be holding any user-visible synchronization locks when finalize is
 * invoked. If an uncaught exception is thrown by the finalize method,
 * the exception is ignored and finalization of that object terminates.
 * <p>
 * After the {@code finalize} method has been invoked for an object, no
 * further action is taken until the Java virtual machine has again
 * determined that there is no longer any means by which this object can
 * be accessed by any thread that has not yet died, including possible
 * actions by other objects or classes which are ready to be finalized,
 * at which point the object may be discarded.
 * <p>
 * The {@code finalize} method is never invoked more than once by a Java
 * virtual machine for any given object.
 * <p>
 * Any exception thrown by the {@code finalize} method causes
 * the finalization of this object to be halted, but is otherwise
 * ignored.
 *
 * @apiNote
 * Classes that embed non-heap resources have many options
 * for cleanup of those resources. The class must ensure that the
 * lifetime of each instance is longer than that of any resource it embeds.
 * {@link java.lang.ref.Reference#reachabilityFence} can be used to ensure that
 * objects remain reachable while resources embedded in the object are in use.
 * <p>
 * A subclass should avoid overriding the {@code finalize} method
 * unless the subclass embeds non-heap resources that must be cleaned up
 * before the instance is collected.
 * Finalizer invocations are not automatically chained, unlike constructors.
 * If a subclass overrides {@code finalize} it must invoke the superclass
 * finalizer explicitly.
 * To guard against exceptions prematurely terminating the finalize chain,
 * the subclass should use a {@code try-finally} block to ensure
 * {@code super.finalize()} is always invoked. For example,
 * <pre>{@code @Override
 * protected void finalize() throws Throwable {
 * try {
 * ... // cleanup subclass state
 * } finally {
 * super.finalize();
 * }
 * }
 * }</pre>
 *
 * @deprecated The finalization mechanism is inherently problematic.
 * Finalization can lead to performance issues, deadlocks, and hangs.
 * Errors in finalizers can lead to resource leaks; there is no way to cancel
 * finalization if it is no longer necessary; and no ordering is specified
 * among calls to {@code finalize} methods of different objects.
 * Furthermore, there are no guarantees regarding the timing of finalization.
 * The {@code finalize} method might be called on a finalizable object
 * only after an indefinite delay, if at all.
 *
 * Classes whose instances hold non-heap resources should provide a method
 * to enable explicit release of those resources, and they should also
 * implement {@link AutoCloseable} if appropriate.
 * The {@link java.lang.ref.Cleaner} and {@link java.lang.ref.PhantomReference}
 * provide more flexible and efficient ways to release resources when an object
 * becomes unreachable.
 *
 * @throws Throwable the {@code Exception} raised by this method
 * @see java.lang.ref.WeakReference
 * @see java.lang.ref.PhantomReference
 * @jls 12.6 Finalization of Class Instances
 */
 @Deprecated(since="9")
 protected void finalize() throws Throwable { }
}