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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* accompanied this code).
*
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* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
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package java.lang;
import jdk.internal.HotSpotIntrinsicCandidate;
Class Object is the root of the class hierarchy. Every class has Object as a superclass. All objects, including arrays, implement the methods of this class. Author: unascribed See Also: Since: 1.0
/**
* 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.
/**
* Constructs a new object.
*/
@HotSpotIntrinsicCandidate
public Object() {}
Returns the runtime class of this Object. The returned Class object is the object that is locked by
static synchronized methods of the represented class. The actual result type is Class<? extends |X|> where |X| is the erasure of the static type of the expression on which getClass is called. For
example, no cast is required in this code fragment:
Number n = 0;
Class<? extends Number> c = n.getClass();
Returns: The Class object that represents the runtime class of this object. @jls 15.8.2 Class Literals
/**
* 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 HashMap. The general contract of hashCode is:
- Whenever it is invoked on the same object more than once during an execution of a Java application, the
hashCode method must consistently return the same integer, provided no information used in 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. - If two objects are equal according to the
equals(Object) method, then calling the hashCode method on each of the two objects must produce the same integer result. - It is not required that if two objects are unequal according to the
equals(Object) method, then calling the 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.
As much as is reasonably practical, the hashCode method defined by class 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.)
See Also: Returns: a hash code value for this object.
/**
* 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.
The equals method implements an equivalence relation on non-null object references:
- It is reflexive: for any non-null reference value
x, x.equals(x) should return true. - It is symmetric: for any non-null reference values
x and y, x.equals(y) should return true if and only if y.equals(x) returns true. - It is transitive: for any non-null reference values
x, y, and z, if x.equals(y) returns true and y.equals(z) returns true, then x.equals(z) should return true. - It is consistent: for any non-null reference values
x and y, multiple invocations of x.equals(y) consistently return true or consistently return false, provided no information used in equals comparisons on the objects is modified. - For any non-null reference value
x, x.equals(null) should return false.
The equals method for class Object implements the most discriminating possible equivalence relation on objects; that is, for any non-null reference values x and y, this method returns true if and only if x and y refer to the same object (x == y has the value true).
Note that it is generally necessary to override the hashCode method whenever this method is overridden, so as to maintain the general contract for the hashCode method, which states that equal objects must have equal hash codes.
Params: - obj – the reference object with which to compare.
See Also: Returns: true if this object is the same as the obj argument; false otherwise.
/**
* 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 x, the expression:
x.clone() != x
will be true, and that the expression:
x.clone().getClass() == x.getClass()
will be true, but these are not absolute requirements. While it is typically the case that:
x.clone().equals(x)
will be true, this is not an absolute requirement. By convention, the returned object should be obtained by calling super.clone. If a class and all of its superclasses (except Object) obey this convention, it will be the case that 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 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 super.clone need to be modified.
The method clone for class Object performs a specific cloning operation. First, if the class of this object does not implement the interface Cloneable, then a CloneNotSupportedException is thrown. Note that all arrays are considered to implement the interface Cloneable and that the return type of the clone method of an array type T[] is 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 Object does not itself implement the interface Cloneable, so calling the clone method on an object whose class is Object will result in throwing an exception at run time.
Throws: - CloneNotSupportedException – if the object's class does not support the
Cloneable interface. Subclasses that override the clone method can also throw this exception to indicate that an instance cannot be cloned.
See Also: Returns: a clone of this instance.
/**
* 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 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 toString method for class Object returns a string consisting of the name of the class of which the object is an instance, the at-sign character `@', 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())
Returns: a string representation of the object.
/**
* 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 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:
- By executing a synchronized instance method of that object.
- By executing the body of a
synchronized statement that synchronizes on the object. - For objects of type
Class, by executing a synchronized static method of that class.
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 Also:
/**
* 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 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 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 Also:
/**
* 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 notified or interrupted.
In all respects, this method behaves as if wait(0L, 0) had been called. See the specification of the wait(long, int) method for details.
Throws: - IllegalMonitorStateException – if the current thread is not
the owner of the object's monitor
- 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 Also:
/**
* 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 notified or interrupted, or until a
certain amount of real time has elapsed.
In all respects, this method behaves as if wait(timeout, 0) had been called. See the specification of the wait(long, int) method for details.
Params: - timeout – the maximum time to wait, in milliseconds
Throws: - IllegalArgumentException – if the value of
timeout is negative - IllegalMonitorStateException – if the current thread is not
the owner of the object's monitor
- 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 Also:
/**
* 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(timeout, 0)}
* had been called. See the specification of the {@link #wait(long, int)} method
* for details.
*
* @param timeout the maximum time to wait, in milliseconds
* @throws IllegalArgumentException if the value of {@code timeout} 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 timeout) 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 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:
- Some other thread invokes the
notify method for this object and thread T happens to be arbitrarily chosen as
the thread to be awakened.
- Some other thread invokes the
notifyAll method for this object. - Some other thread interrupts thread T.
- The specified amount of real time has elapsed, more or less. The amount of real time, in nanoseconds, is given by the expression
1000000 * timeout + nanos. If timeout and nanos are both zero, then real time is not taken into consideration and the thread waits until awakened by one of the other causes. - Thread T is awakened spuriously. (See below.)
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 wait method was invoked. Thread T then returns from the invocation of the wait method. Thus, on return from the wait method, the synchronization state of the object and of thread T is exactly as it was when the 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 interrupted by any thread before or while it is waiting, then an 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.
Params: - timeout – the maximum time to wait, in milliseconds
- nanos – additional time, in nanoseconds, in the range range 0-999999 inclusive
Throws: - IllegalArgumentException – if the value of
timeout is negative, or if the value of nanos is out of range - IllegalMonitorStateException – if the current thread is not
the owner of the object's monitor
- 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 Also: API Note: The recommended approach to waiting is to check the condition being awaited in a while loop around the call to wait, as shown in the example below. Among other things, this approach avoids problems that can be caused by spurious wakeups.
synchronized (obj) {
while (<condition does not hold> and <timeout not exceeded>) {
long timeout = ... ; // recompute timeout values
int nanos = ... ;
obj.wait(timeout, nanos);
}
... // Perform action appropriate to condition or timeout
}
/**
* 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 * timeout + nanos}. If {@code timeout} 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 timeout = ... ; // recompute timeout values
* int nanos = ... ;
* obj.wait(timeout, nanos);
* }
* ... // Perform action appropriate to condition or timeout
* }
* }</pre>
*
* @param timeout the maximum time to wait, in milliseconds
* @param nanos additional time, in nanoseconds, in the range range 0-999999 inclusive
* @throws IllegalArgumentException if the value of {@code timeout} 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 timeout, int nanos) throws InterruptedException {
if (timeout < 0) {
throw new IllegalArgumentException("timeout value is negative");
}
if (nanos < 0 || nanos > 999999) {
throw new IllegalArgumentException(
"nanosecond timeout value out of range");
}
if (nanos > 0) {
timeout++;
}
wait(timeout);
}
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 finalize method to dispose of system resources or to perform other cleanup. The general contract of 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 finalize method may take any action, including making this object available again to other threads; the usual purpose of 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 finalize method of class Object performs no special action; it simply returns normally. Subclasses of Object may override this definition.
The Java programming language does not guarantee which thread will invoke the 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 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 finalize method is never invoked more than once by a Java virtual machine for any given object.
Any exception thrown by the finalize method causes the finalization of this object to be halted, but is otherwise ignored.
Throws: - Throwable – the
Exception raised by this method
See Also: API Note: 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. 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 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 finalize it must invoke the superclass finalizer explicitly. To guard against exceptions prematurely terminating the finalize chain, the subclass should use a try-finally block to ensure super.finalize() is always invoked. For example,
@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 finalize methods of different objects. Furthermore, there are no guarantees regarding the timing of finalization. The 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 AutoCloseable if appropriate. The Cleaner and PhantomReference provide more flexible and efficient ways to release resources when an object becomes unreachable. @jls 12.6 Finalization of Class Instances
/**
* 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.
* <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 { }
}