Java Object class
The Java Object class is the parent class of all classes, that is, all classes in Java inherit object, and subclasses can use all methods of object. Object fully embodies the use of object-oriented inheritance! The object class is located in Java Lang package will be imported automatically during compilation. When we create a class, if we do not explicitly inherit a parent class, it will automatically inherit object and become a subclass of object.
Here are the main methods:
Java Object getClass() method
The Object getClass() method is used to get the class of the runtime object of the object.
Rookie tutorial Java Object getClass() method instance
Chinese translation:
Returns the runtime Class of this Object. The returned Class Object is the Object locked by the static synchronized method of the represented Class.
The actual result type is class <? extends |X|> Class<? Extensions | x 124> where | x | is the erasure of the static type of the expression calling getClass. For example, no cast is required in this code snippet:
Number n = 0; Class<? extends Number> c = n.getClass();
Return value:
A Class object that represents the runtime Class of this 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
*/
public final native Class<?> getClass();
Java Object hashCode() method
The Object hashCode() method is used to obtain the hash value of the object.
Rookie tutorial Java Object hashCode() method instance
Chinese translation:
Returns the hash code value of the object. This method is supported to facilitate hash tables, such as Java util. Hash table provided by HashMap.
The total contract of hashCode is:
During the execution of a Java application, as long as it is called multiple times on the same object, the hashCode method must always return the same integer, provided that the information used in the equals comparison of the object has not been modified. This integer does not need to be 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, calling the hashCode method on each of the two objects must produce the same integer result.
This is not necessary: if the two objects are based on the unequal equals(Object) method, then calling hashCode in each of the two objects must produce different integer results. However, programmers should be aware that generating different integer results for unequal objects may improve the performance of hash tables.
As practical as possible, the hashCode method defined by class Object does return different integers for different objects. This is usually achieved by converting the internal address of the Object to an integer, but Java ™ Programming languages do not need this implementation technology.)
Return value:
The hash code value for this object.
See:
equals(Object) , System.identityHashCode
/**
* 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. (This is typically implemented by converting the internal
* address of the object into an integer, but this implementation
* technique is not required by the
* Java™ programming language.)
*
* @return a hash code value for this object.
* @see java.lang.Object#equals(java.lang.Object)
* @see java.lang.System#identityHashCode
*/
public native int hashCode();
Java Object equals() method
The Object equals() method is used to compare whether two objects are equal.
The equals() method compares two objects to determine whether the two object references point to the same object, that is, to compare whether the memory addresses of the two objects are equal.
Note: if the subclass overrides the equals() method, you need to override the hashCode() method. For example, the String class overrides both the equals() method and the hashCode() method.
Rookie tutorial Java Object equals() method instance
Chinese translation:
Indicates whether some other object is "equal" to this object.
The equals method implements equivalence relations on non empty object references:
It is reflexive: x.equals(x) should return true for any non null reference value X.
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, x.equals(y) calls multiple times always return true or always return false, provided that the information used in the equals comparison on the object is not modified.
x.equals(null) should return false for any non null reference value x.
The equals method of Object class implements the most distinctive possible equivalence relationship on Object; 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 (the value of x == y is true).
Note that whenever you override this method, you usually need to override the hashCode method to maintain the general convention of the hashCode method, that is, equal objects must have equal hash codes.
Parameters:
obj – the reference object to compare with.
Return value:
true if this object is the same as the obj parameter; Otherwise, it is false.
See:
hashCode() , java.util.HashMap
/**
* 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);
}
Java Object clone() method
The Object clone() method is used to create and return a copy of an object.
The clone method is a shallow copy. The object referenced by the attribute in the object will only copy the reference address without reallocating the memory of the referenced object. The corresponding deep copy will recreate even the referenced object.
Rookie tutorial Java Object clone() method instance
The Chinese translation is as follows:
Create and return a copy of this object. The exact meaning of "copy" may depend on the category of the object. The general intent is that for any object x, the expression:
x.clone() != x
Will be true and the expression:
x.clone().getClass() == x.getClass() will be true, but these are not absolute requirements. Although the usual situation is:
x.clone().equals(x) will be true, which is not an absolute requirement.
By convention, the returned Object should be returned by calling super Clone to get. If a class and all its superclasses (except Object) abide by this Convention, then X. clone() getClass() == x.getClass() .
By convention, the object returned by this method should be independent of this object (it is cloned). To achieve this independence, you may need to modify super. Before returning One {or more fields of the object returned by clone. Typically, this means copying any mutable objects that contain the internal "deep structure" of the cloned object and replacing references to these objects with references to copies. If a class contains only original fields or references to immutable objects, usually super There are no fields in the object returned by clone that need to be modified.
The clone method of class Object performs specific cloning operations. First, if the Object's class does not implement the interface clonable, a CloneNotSupportedException is thrown. Note that all arrays are considered to implement the interface clonable, and the return type of the clone method of array type T [] is t [], where t is any reference or primitive type. Otherwise, this method will create a new instance of the class of this Object and initialize all its fields with the contents of the corresponding fields of this Object, just like assignment; The contents of the field itself are not cloned. Therefore, this method performs a "shallow copy" of this Object instead of a "deep copy" operation.
Class Object itself does not implement the interface Cloneable, so calling the clone method on an Object with class Object will cause an exception to be thrown at run time.
Return value:
Clone of this instance.
Top:
CloneNotSupportedException – if the object's class does not support the clonable interface. Subclasses that override the clone method can also throw this exception to indicate that the instance cannot be cloned.
See:
Cloneable
The source code is as follows:
/**
* 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
*/
protected native Object clone() throws CloneNotSupportedException;
Java Object toString() method
The Object toString() method returns a string representation of an object.
Rookie tutorial Java Object toString() method instance
Chinese translation:
Returns the string representation of the object. Typically, the toString method returns a string that "represents" the object in text. The result should be a concise but informative representation that is easy to read. It is recommended that all subclasses override this method.
The toString method of class Object returns a string consisting of the name of the class whose Object is its instance, the at symbol "@" and the unsigned hexadecimal representation of the Object hash code. In other words, this method returns a string equal to:
getClass().getName() + '@' + Integer.toHexString(hashCode())
Return value:
The 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());
}
Java Object notify() method
The Object notify() method is used to wake up a thread waiting on this object monitor.
If all threads wait on this object, only one thread will be selected. The selection is arbitrary and occurs when a decision is made on the implementation.
A thread waiting on the object monitor can call the wait() method.
The notify() method can only be called by a thread that is the owner of this object monitor.
To become the owner of an object monitor, a thread can use the following three methods:
Synchronous instance method of execution object
Use synchronized built-in lock
For objects of Class type, execute synchronous static methods
Only one thread can have a monitor of an object at a time.
If the current thread is not the owner of this object monitor, an IllegalMonitorStateException will be thrown.
Rookie tutorial Java Object notify() method instance
Chinese translation:
Wake up a single thread waiting on this object's monitor. If any thread is waiting for the object, select one of the threads to wake up. The choice is arbitrary and is determined by the implementation. The thread waits on the object's monitor by calling one of the wait methods.
The awakened thread cannot continue until the current thread relinquishes the lock on the object. The awakened thread will compete in the usual way with any other thread that may be actively competing to synchronize this object; For example, the awakened thread has no reliable privileges or disadvantages when it becomes the next thread to lock the object.
This method can only be called by a thread that is the owner of this object monitor. A thread becomes the owner of an object monitor in one of three ways:
By executing the synchronization instance method of the object.
By executing the synchronized statement of the synchronized object.
For an object Class of Class type, execute the synchronous static method of the Class.
Only one thread can have a monitor of one object at a time.
Top:
IllegalMonitorStateException – if the current thread is not the owner of this object monitor.
See:
notifyAll() ， wait()
/**
* 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()
*/
public final native void notify();
Java Object notifyAll() method
The Object notifyAll() method wakes up all threads waiting on the object.
The notifyAll() method is the same as the notify() method, except that the notifyAll() method wakes up all threads waiting on this object monitor, and the notify() method is a thread.
If the current thread is not the owner of the object monitor, calling the notifyAll() method will also cause an IllegalMonitorStateException.
Rookie tutorial Java Object notifyAll() method instance
Chinese translation:
Wake up all threads waiting on this object monitor. The thread waits on the object's monitor by calling one of the wait methods.
The awakened thread cannot continue until the current thread relinquishes the lock on the object. The awakened thread will compete in the usual way with any other thread that may be actively competing to synchronize this object; For example, the awakened thread does not enjoy reliable privileges or disadvantages when it becomes the next thread to lock the object.
This method can only be called by a thread that is the owner of this object monitor. For a description of how a thread can become the owner of a monitor, see the notify method.
Top:
IllegalMonitorStateException – if the current thread is not the owner of this object monitor.
See:
notify() ， wait()
/**
* 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()
*/
public final native void notifyAll();
Java Object wait() method
The Object wait() method puts the current thread into a waiting state. Until another thread calls the notify() method or notifyAll() method of this object.
The current thread must be the monitor owner of this object, otherwise an IllegalMonitorStateException will still occur.
If the current thread is interrupted by any thread before or while waiting, an InterruptedException exception is thrown.
Rookie tutorial Java Object wait() method instance
Chinese translation:
Causes the current thread to wait until another thread calls the notify() method or notifyAll() method for this object. In other words, the method behaves as if it were simply executing a call to wait(0).
The current thread must have a monitor for this object. The thread releases ownership of this monitor and waits until another thread wakes up by calling the notify method or notifyAll method to notify the thread waiting on this object monitor. The thread then waits until it can regain ownership of the monitor and resume execution.
As with the single parameter version, interrupts and false wakes are possible, and this method should always be used in the loop:
synchronized (obj) {
while ()
obj.wait();
... // Perform action appropriate to condition
}
This method can only be called by a thread that is the owner of this object monitor. For a description of how a thread can become the owner of a monitor, see the notify method.
Top:
IllegalMonitorStateException – if the current thread is not the owner of the object monitor.
InterruptedException – if any thread interrupts the current thread before or during the current thread waiting for notification. Clears the interrupt state of the current thread when this exception is thrown.
See:
notify() ， notify() notifyAll()
/**
* 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>
* synchronized (obj) {
* while (<condition does not hold>)
* obj.wait();
* ... // Perform action appropriate to condition
* }
* </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
* the owner of the object's monitor.
* @throws InterruptedException if any thread interrupted the
* current thread before or while the current thread
* was waiting for a notification. The <i>interrupted
* status</i> of the current thread is cleared when
* this exception is thrown.
* @see java.lang.Object#notify()
* @see java.lang.Object#notifyAll()
*/
public final void wait() throws InterruptedException {
wait(0);
}
Java Object wait(long timeout) method
The Object wait(long timeout) method keeps the current thread in a waiting (blocking) state until other threads call the notify() method or notifyAll() method of the object, or exceed the timeout set by the parameter timeout.
If the timeout parameter is 0, it will not time out and will wait all the time, similar to the wait() method.
The current thread must be the monitor owner of this object, otherwise an IllegalMonitorStateException will still occur.
If the current thread is interrupted by any thread before or while waiting, an InterruptedException exception is thrown.
If the passed parameter is illegal, an IllegalArgumentException will be thrown.
Rookie tutorial Java Object wait(long timeout) method instance
Chinese translation:
Causes the current thread to wait until another thread calls the notify() method or notifyAll() method for this object, or the specified amount of time has passed.
The current thread must have a monitor for this object.
This method causes the current thread (called T) to place itself in the wait set for this object, and then discard any and all synchronization claims for this object. Thread T is disabled and dormant for thread scheduling purposes until one of the following four conditions occurs:
Some other thread called the notify method for this object, and thread T was just arbitrarily selected as the thread to wake up.
Other threads call the notifyAll method for this object.
Some other threads interrupt thread T.
The specified real-time time has passed more or less. However, if the timeout is zero, the real-time time time is not considered, and the thread just waits until it receives the notification.
Thread T is then removed from the object's waiting set and thread scheduling is re enabled. Then it competes with other threads for the right to synchronize on the object in the usual way; Once it gains control of the object, all its synchronous declarations to the object will revert to the previous state -- that is, to the state when the wait method was called. Thread T then returns from the call to the wait method. Therefore, when returning from the wait method, the synchronization state of the object and thread T is exactly the same as when calling the wait method.
Threads can also wake up without being notified, interrupted or timed out, that is, the so-called false wake-up. Although this rarely happens in practice, the application must prevent it by testing the condition that should cause the thread to wake up, and continue to wait if the condition is not met. In other words, waiting should always happen in a loop, like this:
synchronized (obj) {
while ()
obj.wait(timeout);
... // Perform action appropriate to condition
}
(for more information on this topic, see section 3.2.3 of Doug Lea's "concurrent programming in Java (Second Edition)" (Addison Wesley, 2000) or Joshua Bloch's "Effective Java Programming Language Guide" (Addison Wesley, 2001).
InterruptedException is thrown if the current thread is interrupted before any thread or while waiting. This exception will not be thrown until the locked state of this object is restored as described above.
Note that the wait method puts the current thread into the waiting set of this object, so it only unlocks this object; Any other objects that the current thread might synchronize remain locked while the thread waits.
This method can only be called by a thread that is the owner of this object monitor. For a description of how a thread can become the owner of a monitor, see the notify method.
Parameters:
timeout - the maximum time (in milliseconds) to wait.
Top:
IllegalArgumentException – if the timeout value is negative.
IllegalMonitorStateException – if the current thread is not the owner of the object monitor.
InterruptedException – if any thread interrupts the current thread before or during the current thread waiting for notification. Clears the interrupt state of the current thread when this exception is thrown.
See:
notify() ， notify() 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>
* synchronized (obj) {
* while (<condition does not hold>)
* obj.wait(timeout);
* ... // Perform action appropriate to condition
* }
* </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
* 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 for a notification. The <i>interrupted
* status</i> of the current thread is cleared when
* this exception is thrown.
* @see java.lang.Object#notify()
* @see java.lang.Object#notifyAll()
*/
public final native void wait(long timeout) throws InterruptedException;
public final void wait(long timeout, int nanos) method
Similar to the wait(long timeout) method, there is an additional nanos parameter, which represents the additional time (in nanoseconds, the range is 0-999999). Therefore, nanoseconds should be added to the timeout time.
Chinese translation:
Make the current thread wait until another thread calls the notify() method or notifyAll() method for this object, or some other thread interrupts the current thread, or a certain real-time time time has elapsed.
This method is similar to the wait method of a parameter, but it allows better control over the amount of time to wait for notification before abandoning. The real-time quantity measured in nanoseconds is given by the following formula:
1000000*timeout+nanos
In all other respects, this method performs the same operation as the one parameter method wait(long). In particular, wait(0, 0) has the same meaning as wait(0).
The current thread must have a monitor for this object. The thread releases ownership of this monitor and waits until one of the following two conditions occurs:
Another thread notifies the thread waiting for this object monitor to wake up by calling the notify method or notifyAll method.
The timeout, by specifying timeout milliseconds plus nanos econds, has passed.
The thread then waits until it can regain ownership of the monitor and resume execution.
As with the single parameter version, interrupts and false wakes are possible, and this method should always be used in the loop:
synchronized (obj) {
while ()
obj.wait(timeout, nanos);
... // Perform action appropriate to condition
}
This method can only be called by a thread that is the owner of this object monitor. For a description of how a thread can become the owner of a monitor, see the notify method.
Parameters:
timeout - the maximum time (in milliseconds) to wait.
nanos – extra time, in nanoseconds, in the range of 0-999999.
Top:
IllegalArgumentException - if the value of timeout is negative or the value of nanos is not in the range of 0-999999.
IllegalMonitorStateException – if the current thread is not the owner of this object monitor.
InterruptedException – if any thread interrupts the current thread before or during the current thread waiting for notification. Clears the interrupt state of the current thread when this exception is thrown.
/**
* 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
* to wake up either through a call to the {@code notify} method
* or the {@code notifyAll} method.
* <li>The timeout period, specified by {@code timeout}
* milliseconds plus {@code nanos} nanoseconds arguments, has
* elapsed.
* </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>
* synchronized (obj) {
* while (<condition does not hold>)
* obj.wait(timeout, nanos);
* ... // Perform action appropriate to condition
* }
* </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
* 0-999999.
* @throws IllegalArgumentException if the value of timeout is
* negative or the value of nanos is
* not in the range 0-999999.
* @throws IllegalMonitorStateException if the current thread is not
* the owner of this object's monitor.
* @throws InterruptedException if any thread interrupted the
* current thread before or while the current thread
* was waiting for a notification. The <i>interrupted
* status</i> of the current thread is cleared when
* this exception is thrown.
*/
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);
}
Java Object finalize() method
The Object finalize() method is used for the operation triggered when the instance is collected by the garbage collector.
This method is called by the object's garbage collector when the GC (garbage collector) determines that there are no more references to the object.
Rookie tutorial Java Object finalize() method instance
Chinese translation:
When the garbage collector determines that there is no longer a reference to the object, it is called by the garbage collector on the object. Subclasses override the finalize method to process system resources or perform other cleanup.
The general convention for finalize is that when Java ™ The virtual machine calls this object when it determines that there are no more methods for any thread that has not died to access this object, unless it is taken as a result of the completion of some other prepared object or class. The finalize method can perform any operation, including making the object available to other threads again; However, the general purpose of finalize is to perform cleanup operations before objects are irrevocably discarded. For example, the finalize method of an object representing an input / output connection may perform an explicit I/O transaction to break the connection before the object is permanently discarded.
The finalize method of Object class does not perform any special operations; It just returns normally. The Object subclass can override this definition.
The Java programming language does not guarantee which thread will call the finalize method of any given object. However, it can be guaranteed that the thread calling finalize will not hold any user visible synchronization lock when calling finalize. If the finalize method throws an uncapped exception, it ignores the exception and terminates the termination of the object.
After calling the finalize method for the object, no further operation will be taken until the Java virtual machine determines again that any thread that has not been terminated can no longer access the object, including other objects or classes whose possible operations are prepared to be completed. At this time, the object may be discarded.
The Java virtual machine will never call the finalize method multiple times for any given object.
Any exception thrown by the finalize method will cause the termination of this object to be suspended, but otherwise it will be ignored.
Top:
Throwable – Exception thrown by this method
See:
ref.WeakReference , ref.PhantomReference
/**
* 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.
*
* @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
*/
protected void finalize() throws Throwable { }
}