java.lang
Class ThreadLocal<T>
ThreadLocal objects have a different state associated with every
Thread that accesses them. Every access to the ThreadLocal object
(through the
get() and
set() methods)
only affects the state of the object as seen by the currently
executing Thread.
The first time a ThreadLocal object is accessed on a particular
Thread, the state for that Thread's copy of the local variable is set by
executing the method
initialValue().
An example how you can use this:
class Connection
{
private static ThreadLocal owner = new ThreadLocal()
{
public Object initialValue()
{
return("nobody");
}
};
...
}
Now all instances of connection can see who the owner of the currently
executing Thread is by calling
owner.get(). By default any
Thread would be associated with 'nobody'. But the Connection object could
offer a method that changes the owner associated with the Thread on
which the method was called by calling
owner.put("somebody").
(Such an owner changing method should then be guarded by security checks.)
When a Thread is garbage collected all references to values of
the ThreadLocal objects associated with that Thread are removed.
ThreadLocal()- Creates a ThreadLocal object without associating any value to it yet.
|
protected void | finalize()- Called on an object by the Virtual Machine at most once,
at some point after the Object is determined unreachable
but before it is destroyed.
|
T | get()- Gets the value associated with the ThreadLocal object for the currently
executing Thread.
|
protected T | initialValue()- Called once per thread on the first invocation of get(), if set() was
not already called.
|
void | remove()- Removes the value associated with the ThreadLocal object for the
currently executing Thread.
|
void | set(T value)- Sets the value associated with the ThreadLocal object for the currently
executing Thread.
|
clone, equals, extends Object> getClass, finalize, hashCode, notify, notifyAll, toString, wait, wait, wait |
ThreadLocal
public ThreadLocal()
Creates a ThreadLocal object without associating any value to it yet.
finalize
protected void finalize()
throws Throwable Called on an object by the Virtual Machine at most once,
at some point after the Object is determined unreachable
but before it is destroyed. You would think that this
means it eventually is called on every Object, but this is
not necessarily the case. If execution terminates
abnormally, garbage collection does not always happen.
Thus you cannot rely on this method to always work.
For finer control over garbage collection, use references
from the
java.lang.ref package.
Virtual Machines are free to not call this method if
they can determine that it does nothing important; for
example, if your class extends Object and overrides
finalize to do simply
super.finalize().
finalize() will be called by a
Thread that has no
locks on any Objects, and may be called concurrently.
There are no guarantees on the order in which multiple
objects are finalized. This means that finalize() is
usually unsuited for performing actions that must be
thread-safe, and that your implementation must be
use defensive programming if it is to always work.
If an Exception is thrown from finalize() during garbage
collection, it will be patently ignored and the Object will
still be destroyed.
It is allowed, although not typical, for user code to call
finalize() directly. User invocation does not affect whether
automatic invocation will occur. It is also permitted,
although not recommended, for a finalize() method to "revive"
an object by making it reachable from normal code again.
Unlike constructors, finalize() does not get called
for an object's superclass unless the implementation
specifically calls
super.finalize().
The default implementation does nothing.
- finalize in interface Object
Throwable - permits a subclass to throw anything in an
overridden version; but the default throws nothing
get
public T get()
Gets the value associated with the ThreadLocal object for the currently
executing Thread. If this is the first time the current thread has called
get(), and it has not already called set(), the value is obtained by
initialValue().
- the value of the variable in this thread
initialValue
protected T initialValue()
Called once per thread on the first invocation of get(), if set() was
not already called. The default implementation returns null.
Often, this method is overridden to create the appropriate initial object
for the current thread's view of the ThreadLocal.
- the initial value of the variable in this thread
remove
public void remove()
Removes the value associated with the ThreadLocal object for the
currently executing Thread.
set
public void set(T value)
Sets the value associated with the ThreadLocal object for the currently
executing Thread. This overrides any existing value associated with the
current Thread and prevents initialValue() from being
called if this is the first access to this ThreadLocal in this Thread.
value - the value to set this thread's view of the variable to
ThreadLocal -- a variable with a unique value per thread
Copyright (C) 2000, 2002, 2003, 2006 Free Software Foundation, Inc.
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