JDK8-Object 源码
/**
Creates and returns a copy of this object. The precise meaning
of "copy" may depend on the class of the object. The general
intent【目的】 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【约定】, the returned object should be obtained by calling
{@code super.clone}. If a class and all of its superclasses (except
{@code Object}) obey【服从】 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【易变的】 objects that comprise【由...组成】 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
@see java.lang.Cloneable
*/
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
<li>For objects of type {@code Class,} by executing a
</ul>
<p>
Only one thread at a time can own an object's monitor.
@throws IllegalMonitorStateException if the current thread is not
@see java.lang.Object#notifyAll()
@see java.lang.Object#wait()
*/
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
@see java.lang.Object#notify()
@see java.lang.Object#wait()
*/
public final native void notifyAll();
/**
Causes the current thread to wait until either another thread invokes the
{@link java.lang.Object#notify()} method or the
{@link java.lang.Object#notifyAll()} method for this object, or a
specified amount of time has elapsed.
<p>
The current thread must own this object's monitor.
<p>
This method causes the current thread (call it <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. Thread <var>T</var>
becomes disabled for thread scheduling purposes and lies dormant
until one of four things happens:
<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. If
{@code timeout} is zero, however, then real time is not taken into
consideration and the thread simply waits until notified.
</ul>
The thread <var>T</var> is then removed from the wait set for this
object and re-enabled for thread scheduling. It then competes in the
usual manner with other threads for the right to synchronize on the
object; once it has gained 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 also wake up without being notified, interrupted, or
timing out, a so-called <i>spurious wakeup</i>. 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. In other words,
waits should always occur in loops, like this one:
<pre>
</pre>
(For more information on this topic, see Section 3.2.3 in Doug Lea's
"Concurrent Programming in Java (Second Edition)" (Addison-Wesley,
2000), or Item 50 in Joshua Bloch's "Effective Java Programming
Language Guide" (Addison-Wesley, 2001).
<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. This exception is not
thrown until the lock status of this object has been restored as
described above.
<p>
Note that the {@code wait} method, as it places the current thread
into the wait set for this object, unlocks only this object; any
other objects on which the current thread may be synchronized remain
locked while the thread waits.
<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.
@param timeout the maximum time to wait in milliseconds.
@throws IllegalArgumentException if the value of timeout is
@throws IllegalMonitorStateException if the current thread is not
@throws InterruptedException if any thread interrupted the
@see java.lang.Object#notify()
@see java.lang.Object#notifyAll()
*/
public final native void wait(long timeout) throws InterruptedException;
/**
Causes the current thread to wait until another thread invokes the
{@link java.lang.Object#notify()} method or the
{@link java.lang.Object#notifyAll()} method for this object, or
some other thread interrupts the current thread, or a certain
amount of real time has elapsed.
<p>
This method is similar to the {@code wait} method of one
argument, but it allows finer control over the amount of time to
wait for a notification before giving up. The amount of real time,
measured in nanoseconds, is given by:
<blockquote>
<pre>
1000000*timeout+nanos</pre></blockquote>
<p>
In all other respects, this method does the same thing as the
method {@link #wait(long)} of one argument. In particular,
{@code wait(0, 0)} means the same thing as {@code wait(0)}.
<p>
The current thread must own this object's monitor. The thread
releases ownership of this monitor and waits until either of the
following two conditions has occurred:
<ul>
<li>Another thread notifies threads waiting on this object's monitor
<li>The timeout period, specified by {@code timeout}
</ul>
<p>
The thread then waits until it can re-obtain ownership of the
monitor and resumes execution.
<p>
As in the one argument version, interrupts and spurious wakeups are
possible, and this method should always be used in a loop:
<pre>
</pre>
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.
@param timeout the maximum time to wait in milliseconds.
@param nanos additional time, in nanoseconds range
@throws IllegalArgumentException if the value of timeout is
@throws IllegalMonitorStateException if the current thread is not
@throws InterruptedException if any thread interrupted the
*/
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);
}
/**
Causes the current thread to wait until another thread invokes the
{@link java.lang.Object#notify()} method or the
{@link java.lang.Object#notifyAll()} method for this object.
In other words, this method behaves exactly as if it simply
performs the call {@code wait(0)}.
<p>
The current thread must own this object's monitor. The thread
releases ownership of this monitor and waits until another thread
notifies threads waiting on this object's monitor to wake up
either through a call to the {@code notify} method or the
{@code notifyAll} method. The thread then waits until it can
re-obtain ownership of the monitor and resumes execution.
<p>
As in the one argument version, interrupts and spurious wakeups are
possible, and this method should always be used in a loop:
<pre>
</pre>
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
@throws InterruptedException if any thread interrupted the
@see java.lang.Object#notify()
@see java.lang.Object#notifyAll()
*/
public final void wait() throws InterruptedException {
wait(0);
}
/**
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
还未添加个人签名 2021.11.08 加入
还未添加个人简介
评论