The actual result type is {@code Class} * where {@code |X|} is the erasure of the static type of the * expression on which {@code getClass} is called. For * example, no cast is required in this code fragment:
* *
* {@code Number n = 0; }
* {@code Class c = n.getClass(); }
*
* The general contract of {@code hashCode} is: *
* The {@code equals} method implements an {@index "equivalence relation"} * on non-null object references: *
* An equivalence relation partitions the elements it operates on * into equivalence classes; all the members of an * equivalence class are equal to each other. Members of an * equivalence class are substitutable for each other, at least * for some purposes. * * @implSpec * 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}). * * In other words, under the reference equality equivalence * relation, each equivalence class only has a single element. * * @apiNote * It is generally necessary to override the {@link #hashCode() 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. *
The two-argument {@link java.util.Objects#equals(Object, * Object) Objects.equals} method implements an equivalence relation * on two possibly-null object references. * * @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: *
*
* x.clone() != x
* will be true, and that the expression:
*
*
* x.clone().getClass() == x.getClass()
* will be {@code true}, but these are not absolute requirements.
* While it is typically the case that:
*
*
* x.clone().equals(x)
* will be {@code true}, this is not an absolute requirement.
* * 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()}. *
* 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. * * @implSpec * 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. *
* 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 */ @IntrinsicCandidate protected native Object clone() throws CloneNotSupportedException; /** * {@return a string representation of the object} * * Satisfying this method's contract implies a non-{@code null} * result must be returned. * * @apiNote * 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. * The string output is not necessarily stable over time or across * JVM invocations. * @implSpec * 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: * {@snippet lang=java : * getClass().getName() + '@' + Integer.toHexString(hashCode()) * } * The {@link java.util.Objects#toIdentityString(Object) * Objects.toIdentityString} method returns the string for an * object equal to the string that would be returned if neither * the {@code toString} nor {@code hashCode} methods were * overridden by the object's class. */ 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. *
* 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. *
* 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: *
* 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() */ @IntrinsicCandidate 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. *
* 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. *
* 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() */ @IntrinsicCandidate public final native void notifyAll(); /** * Causes the current thread to wait until it is awakened, typically * by being notified or interrupted. *
* 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 interrupted status 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 notified or interrupted, or until a * certain amount of real time has elapsed. *
* 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 interrupted status of the * current thread is cleared when this exception is thrown. * @see #notify() * @see #notifyAll() * @see #wait() * @see #wait(long, int) */ public final void wait(long timeoutMillis) throws InterruptedException { if (!Thread.currentThread().isVirtual()) { wait0(timeoutMillis); return; } // virtual thread waiting boolean attempted = Blocker.begin(); try { wait0(timeoutMillis); } catch (InterruptedException e) { // virtual thread's interrupt status needs to be cleared Thread.currentThread().getAndClearInterrupt(); throw e; } finally { Blocker.end(attempted); } } // final modifier so method not in vtable private final native void wait0(long timeoutMillis) throws InterruptedException; /** * Causes the current thread to wait until it is awakened, typically * by being notified or interrupted, or until a * certain amount of real time has elapsed. *
* 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. *
* This method causes the current thread (referred to here as T) 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. *
* Thread T then becomes disabled for thread scheduling purposes * and lies dormant until one of the following occurs: *
* The thread T 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 T 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. *
* A thread can wake up without being notified, interrupted, or timing out, a * so-called spurious wakeup. 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. *
* For more information on this topic, see section 14.2, * "Condition Queues," in Brian Goetz and others' Java Concurrency * in Practice (Addison-Wesley, 2006) or Item 81 in Joshua * Bloch's Effective Java, Third Edition (Addison-Wesley, * 2018). *
* 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 interrupted status 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.
*
* {@snippet lang=java :
* synchronized (obj) {
* while (
* When running in a Java virtual machine in which finalization has been
* disabled or removed, the garbage collector will never call
* {@code finalize()}. In a Java virtual machine in which finalization is
* enabled, the garbage collector might call {@code finalize} only after an
* indefinite delay.
*
* 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.
*
* The {@code finalize} method of class {@code Object} performs no
* special action; it simply returns normally. Subclasses of
* {@code Object} may override this definition.
*
* 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.
*
* 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.
*
* The {@code finalize} method is never invoked more than once by a Java
* virtual machine for any given object.
*
* 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.
*
* 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,
* {@snippet lang="java":
* @Override
* protected void finalize() throws Throwable {
* try {
* ... // cleanup subclass state
* } finally {
* super.finalize();
* }
* }
* }
*
* @deprecated Finalization is deprecated and subject to removal in a future
* release. The use of finalization can lead to problems with security,
* performance, and reliability.
* See JEP 421 for
* discussion and alternatives.
*
* Subclasses that override {@code finalize} to perform cleanup should use
* alternative cleanup mechanisms and remove the {@code finalize} method.
* Use {@link java.lang.ref.Cleaner} and
* {@link java.lang.ref.PhantomReference} as safer ways to release resources
* when an object becomes unreachable. Alternatively, add a {@code close}
* method to explicitly release resources, and implement
* {@code AutoCloseable} to enable use of the {@code try}-with-resources
* statement.
*
* This method will remain in place until finalizers have been removed from
* most existing code.
*
* @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", forRemoval=true)
protected void finalize() throws Throwable { }
}