/*

 * 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>

     * <p>

     * As much as is reasonably practical, the hashCode method defined

     * by class {@code Object} does return distinct integers for

     * distinct objects. (The hashCode may or may not be implemented

     * as some function of an object's memory address at some point

     * in time.)

     *

     * @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™ 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.