java.lang.Object | +--java.lang.Thread
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();
Runnable
,
Runtime.exit(int)
,
run()
Field Summary | |
static int |
MAX_PRIORITY
The maximum priority that a thread can have. |
static int |
MIN_PRIORITY
The minimum priority that a thread can have. |
static int |
NORM_PRIORITY
The default priority that is assigned to a thread. |
Constructor Summary | |
Thread()
Allocates a new Thread object. |
|
Thread(Runnable target)
Allocates a new Thread object. |
Method Summary | |
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. |
int |
getPriority()
Returns this thread's priority. |
boolean |
isAlive()
Tests if this thread is alive. |
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. |
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. |
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. |
Methods inherited from class java.lang.Object |
equals,
getClass,
hashCode,
notify,
notifyAll,
wait,
wait,
wait |
Field Detail |
public static final int MIN_PRIORITY
public static final int NORM_PRIORITY
public static final int MAX_PRIORITY
Constructor Detail |
public Thread()
Thread
object. This constructor has
the same effect as Thread(null, null,
gname)
, where gname is
a newly generated name. Automatically generated names are of the
form "Thread-"+
n, where n is an integer.
Threads created this way must have overridden their
run()
method to actually do anything. An example
illustrating this method being used follows:
import java.lang.*; class plain01 implements Runnable { String name; plain01() { name = null; } plain01(String s) { name = s; } public void run() { if (name == null) System.out.println("A new thread created"); else System.out.println("A new thread with name " + name + " created"); } } class threadtest01 { public static void main(String args[] ) { int failed = 0 ; Thread t1 = new Thread(); if (t1 != null) System.out.println("new Thread() succeed"); else { System.out.println("new Thread() failed"); failed++; } } }
Runnable
public Thread(Runnable target)
Thread
object. This constructor has
the same effect as Thread(null, target,
gname)
, where gname is
a newly generated name. Automatically generated names are of the
form "Thread-"+
n, where n is an integer.target
- the object whose run
method is called.Method Detail |
public static Thread currentThread()
public static void yield()
public static void sleep(long millis) throws InterruptedException
millis
- the length of time to sleep in milliseconds.Object.notify()
public void start()
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).
run()
public void run()
Runnable
run object, then that
Runnable
object's run
method is called;
otherwise, this method does nothing and returns.
Subclasses of Thread
should override this method.
start()
,
Runnable.run()
public final boolean isAlive()
true
if this thread is alive;
false
otherwise.public final void setPriority(int newPriority)
newPriority
- priority to set this thread toMIN_PRIORITY
to
MAX_PRIORITY
.getPriority()
,
getPriority()
,
MAX_PRIORITY
,
MIN_PRIORITY
public final int getPriority()
setPriority(int)
,
setPriority(int)
public static int activeCount()
public final void join() throws InterruptedException
public String toString()