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 equivalence relation * on non-null object references: *
* 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}). *
* 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: *
*
* 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. *
* 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 */ @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. *
* 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: *
*
* getClass().getName() + '@' + Integer.toHexString(hashCode())
*
*
* @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.
* * 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() */ @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. *
* 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() */ @HotSpotIntrinsicCandidate 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 native void wait(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 69 in Joshua * Bloch's Effective Java, Second Edition (Addison-Wesley, * 2008). *
* 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. * *
{@code
* synchronized (obj) {
* while ( and ) {
* long timeoutMillis = ... ; // recompute timeout values
* int nanos = ... ;
* obj.wait(timeoutMillis, nanos);
* }
* ... // Perform action appropriate to condition or timeout
* }
* }
*
* @param timeoutMillis the maximum time to wait, in milliseconds
* @param nanos additional time, in nanoseconds, in the 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 interrupted status 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.
* * 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, *
{@code @Override
* protected void finalize() throws Throwable {
* try {
* ... // cleanup subclass state
* } finally {
* super.finalize();
* }
* }
* }
*
* @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 { }
}