| java.lang.Object | |
| ↳ | java.lang.Thread |
Class Overview
A thread is a thread of execution in a program. The Java Virtual Machine allows an application to have multiple threads of execution running concurrently.
Every thread has a priority. Threads with higher priority are executed in preference to threads with lower priority.
There are two ways to create a new thread of execution. One is to declare a
class to be a subclass of Thread. This subclass should override
the run method of class Thread. An instance of the
subclass can then be allocated and started. For example, a thread that
computes primes larger than a stated value could be written as follows:
class PrimeThread extends Thread {
long minPrime;
PrimeThread(long minPrime) {
this.minPrime = minPrime;
}
public void run() {
// compute primes larger than minPrime
. . .
}
}
The following code would then create a thread and start it running:
PrimeThread p = new PrimeThread(143); p.start();
The other way to create a thread is to declare a class that implements the
Runnable interface. That class then implements the
run method. An instance of the class can then be allocated,
passed as an argument when creating Thread, and started. The
same example in this other style looks like the following:
class PrimeRun implements Runnable {
long minPrime;
PrimeRun(long minPrime) {
this.minPrime = minPrime;
}
public void run() {
// compute primes larger than minPrime
. . .
}
}
The following code would then create a thread and start it running:
PrimeRun p = new PrimeRun(143); new Thread(p).start();
Summary
| Constants | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| int | MAX_PRIORITY | The maximum priority that a thread can have. | |||||||||
| int | MIN_PRIORITY | The minimum priority that a thread can have. | |||||||||
| int | NORM_PRIORITY | The default priority that is assigned to a thread. | |||||||||
| Public Constructors | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
|
Thread()
Allocates a new
Thread object. | |||||||||||
|
Thread(Runnable target)
Allocates a new
Thread object with a specific target object
whose run method is called. | |||||||||||
| Public Methods | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| static int |
activeCount()
Returns the current number of active threads in the VM.
| ||||||||||
| static Thread |
currentThread()
Returns a reference to the currently executing thread object.
| ||||||||||
| final int |
getPriority()
Returns this thread's priority.
| ||||||||||
| void |
interrupt()
Interrupts this thread.
| ||||||||||
| final boolean |
isAlive()
Tests if this thread is alive.
| ||||||||||
| synchronized final void |
join()
Waits for this thread to die.
| ||||||||||
| void |
run()
If this thread was constructed using a separate
Runnable run
object, then that Runnable object's run method is
called; otherwise, this method does nothing and returns. | ||||||||||
| final void |
setPriority(int newPriority)
Changes the priority of this thread.
| ||||||||||
| static void |
sleep(long millis)
Causes the currently executing thread to sleep (temporarily cease execution)
for the specified number of milliseconds.
| ||||||||||
| synchronized void |
start()
Causes this thread to begin execution; the Java Virtual Machine calls the
run method of this thread. | ||||||||||
| String |
toString()
Returns a string representation of this thread, including a unique number
that identifies the thread and the thread's priority.
| ||||||||||
| static void |
yield()
Causes the currently executing thread object to temporarily pause and allow
other threads to execute.
| ||||||||||
|
[Expand]
Inherited Methods | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
From class
java.lang.Object
| |||||||||||
|
From interface
java.lang.Runnable
| |||||||||||
Constants
public static final int MAX_PRIORITY
The maximum priority that a thread can have.
public static final int MIN_PRIORITY
The minimum priority that a thread can have.
public static final int NORM_PRIORITY
The default priority that is assigned to a thread.
Public Constructors
public Thread ()
Allocates a new Thread object.
Threads created this way must have overridden their run() method
to actually do anything.
See Also
public Thread (Runnable target)
Allocates a new Thread object with a specific target object
whose run method is called.
Parameters
| target | the object whose run method is called.
|
|---|
Public Methods
public static int activeCount ()
Returns the current number of active threads in the VM.
Returns
- the current number of active threads.
public static Thread currentThread ()
Returns a reference to the currently executing thread object.
Returns
- the currently executing thread.
public final int getPriority ()
Returns this thread's priority.
Returns
- this thread's priority.
See Also
public void interrupt ()
Interrupts this thread.
If this thread is blocked in an invocation of the wait() method of the Object class, or of the join(),
sleep(long) methods of this class, then its interrupt status will be
cleared and it will receive an InterruptedException.
If none of the previous conditions hold then this thread's interrupt status will be set.
Interrupting a thread that is not alive need not have any effect.
public final boolean isAlive ()
Tests if this thread is alive. A thread is alive if it has been started and has not yet died.
Returns
trueif this thread is alive;falseotherwise.
public final synchronized void join ()
Waits for this thread to die.
Throws
| InterruptedException | if another thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown. |
|---|
public void run ()
public final void setPriority (int newPriority)
Changes the priority of this thread.
Parameters
| newPriority | priority to set this thread to |
|---|
Throws
| IllegalArgumentException | If the priority is not in the range MIN_PRIORITY
to MAX_PRIORITY. |
|---|
public static void sleep (long millis)
Causes the currently executing thread to sleep (temporarily cease execution) for the specified number of milliseconds. The thread does not lose ownership of any monitors.
Parameters
| millis | the length of time to sleep in milliseconds. |
|---|
Throws
| InterruptedException | if another thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown. |
|---|
See Also
public synchronized void start ()
Causes this thread to begin execution; the Java Virtual Machine calls the
run method of this thread.
The result is that two threads are running concurrently: the current thread
(which returns from the call to the start method) and the other
thread (which executes its run method).
Throws
| IllegalThreadStateException | if the thread was already started. |
|---|
See Also
public String toString ()
Returns a string representation of this thread, including a unique number that identifies the thread and the thread's priority.
Returns
- a string representation of this thread.
public static void yield ()
Causes the currently executing thread object to temporarily pause and allow other threads to execute.