fixed some formatting typos

[vimdoclet.git] / sample / java.lang.Object.txt

*java.lang.Object* *Object* Class Object is the root of the class hierarchy.

public class Object


|java.lang.Object_Description|
|java.lang.Object_Fields|
|java.lang.Object_Constructors|
|java.lang.Object_Methods|

================================================================================

*java.lang.Object_Constructors*
|java.lang.Object()|

*java.lang.Object_Methods*
|java.lang.Object.clone()|Creates and returns a copy of this object.
|java.lang.Object.equals(Object)|Indicates whether some other object is "equal 
|java.lang.Object.finalize()|Called by the garbage collector on an object when 
|java.lang.Object.getClass()|Returns the runtime class of thisObject.
|java.lang.Object.hashCode()|Returns a hash code value for the object.
|java.lang.Object.notify()|Wakes up a single thread that is waiting on this obj
|java.lang.Object.notifyAll()|Wakes up all threads that are waiting on this obj
|java.lang.Object.toString()|Returns a string representation of the object.
|java.lang.Object.wait()|Causes the current thread to wait until another thread
|java.lang.Object.wait(long)|Causes the current thread to wait until either ano
|java.lang.Object.wait(long,int)|Causes the current thread to wait until anothe

*java.lang.Object_Description*

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. 



*java.lang.Object()*

public Object()




*java.lang.Object.clone()*

protected native |java.lang.Object| clone()
  throws |java.lang.CloneNotSupportedException|
         
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. 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. 



    Returns: a clone of this instance. 

*java.lang.Object.equals(Object)*

public boolean equals(java.lang.Object obj)

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. 


    obj - the reference object with which to compare. 

    Returns: true if this object is the same as the obj argument; false otherwise. 

*java.lang.Object.finalize()*

protected void finalize()
  throws |java.lang.Throwable|
         
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 JavaTM 
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. 



*java.lang.Object.getClass()*

public final native |java.lang.Class|<?> getClass()

Returns the runtime class of thisObject. The returnedClassobject is the object 
that is locked bystatic synchronizedmethods of the represented class. 

The actual result type isClasswhere|X|is the erasure of the static type of the 
expression on whichgetClassis called. For example, no cast is required in this 
code fragment: 

Number n = 0;Class c = n.getClass(); 



    Returns: The {@code Class} object that represents the runtime class of this object. 

*java.lang.Object.hashCode()*

public native int hashCode()

Returns a hash code value for the object. This method is supported for the 
benefit of hashtables such as those provided by java.util.Hashtable. 

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 (|java.lang.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 hashtables. 

As much as is reasonably practical, the hashCode method defined by class 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 JavaTM programming 
language.) 



    Returns: a hash code value for this object. 

*java.lang.Object.notify()*

public final native void notify()

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. 



*java.lang.Object.notifyAll()*

public final native void notifyAll()

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. 



*java.lang.Object.toString()*

public |java.lang.String| toString()

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. 

*java.lang.Object.wait()*

public final void wait()
  throws |java.lang.InterruptedException|
         
Causes the current thread to wait until another thread invokes the 
(|java.lang.Object|) method or the (|java.lang.Object|) method for this object. 
In other words, this method behaves exactly as if it simply performs the call 
wait(0). 

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 notify 
method or the notifyAll method. The thread then waits until it can re-obtain 
ownership of the monitor and resumes execution. 

As in the one argument version, interrupts and spurious wakeups are possible, 
and this method should always be used in a loop: 

synchronized (obj) { while (<condition does not hold>) obj.wait(); ... // 
Perform action appropriate to condition } 

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. 



*java.lang.Object.wait(long)*

public final native void wait(long timeout)
  throws |java.lang.InterruptedException|
         
Causes the current thread to wait until either another thread invokes the 
(|java.lang.Object|) method or the (|java.lang.Object|) method for this object, 
or a specified amount of time has elapsed. 

The current thread must own this object's monitor. 

This method causes the current thread (call it T) to place itself in the wait 
set for this object and then to relinquish any and all synchronization claims 
on this object. Thread T becomes disabled for thread scheduling purposes and 
lies dormant until one of four things happens: 

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(|java.lang.Thread|) thread T. The specified amount of real time has 
elapsed, more or less. If timeout is zero, however, then real time is not taken 
into consideration and the thread simply waits until notified. 

The thread T 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 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 also 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. In other words, waits should always occur in loops, like this 
one: 

synchronized (obj) { while (<condition does not hold>) obj.wait(timeout); ... 
// Perform action appropriate to condition } 

(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). 

If the current thread is interrupted(|java.lang.Thread|) by any thread before 
or while it is waiting, then an InterruptedException is thrown. This exception 
is not thrown until the lock status of this object has been restored as 
described above. 

Note that the 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. 

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. 


    timeout - the maximum time to wait in milliseconds. 

*java.lang.Object.wait(long,int)*

public final void wait(
  long timeout,
  int nanos)
  throws |java.lang.InterruptedException|
         
Causes the current thread to wait until another thread invokes the 
(|java.lang.Object|) method or the (|java.lang.Object|) method for this object, 
or some other thread interrupts the current thread, or a certain amount of real 
time has elapsed. 

This method is similar to the 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: 



1000000*timeout+nanos 

In all other respects, this method does the same thing as the method 
(|java.lang.Object|) of one argument. In particular, wait(0, 0) means the same 
thing as wait(0). 

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: 

Another thread notifies threads waiting on this object's monitor to wake up 
either through a call to the notify method or the notifyAll method. The timeout 
period, specified by timeout milliseconds plus nanos nanoseconds arguments, has 
elapsed. 

The thread then waits until it can re-obtain ownership of the monitor and 
resumes execution. 

As in the one argument version, interrupts and spurious wakeups are possible, 
and this method should always be used in a loop: 

synchronized (obj) { while (<condition does not hold>) obj.wait(timeout, 
nanos); ... // Perform action appropriate to condition } 

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. 


    timeout - the maximum time to wait in milliseconds. 
    nanos - additional time, in nanoseconds range 0-999999.