This section you will see the life cycle of thread in java.
Life Cycle of A Thread
When you are programming with threads, understanding the life cycle of thread is very valuable. While a thread is alive, it is in one of several states. By invoking start() method, it doesn?t mean that the thread has access to CPU and start executing straight away. Several factors determine how it will proceed.
Different states of a thread are :
- New state ? After the creations of Thread instance the thread is in this state but before the start() method invocation. At this point, the thread is considered not alive.
- Runnable (Ready-to-run) state ? A thread start its life from Runnable state. A thread first enters runnable state after the invoking of start() method but a thread can return to this state after either running, waiting, sleeping or coming back from blocked state also. On this state a thread is waiting for a turn on the processor.
- Running state ? A thread is in running state that means the thread is currently executing. There are several ways to enter in Runnable state but there is only one way to enter in Running state: the scheduler select a thread from runnable pool.
- Dead state ? A thread can be considered dead when its run() method completes. If any thread comes on this state that means it cannot ever run again.
- Blocked - A thread can enter in this state because of waiting the resources that are hold by another thread.
Different states implementing Multiple-Threads are:
- Sleeping ? On this state, the thread is
still alive but it is not runnable, it might be return to runnable state later,
if a particular event occurs. On this state a thread sleeps for a specified
amount of time. You can use the method sleep( ) to stop the running
state of a thread.
static void sleep(long millisecond) throws InterruptedException
- Waiting for Notification ? A thread waits
for notification from another thread. The thread sends back to runnable
state after sending notification from another thread.
final void wait(long timeout) throws InterruptedException
final void wait(long timeout, int nanos) throws InterruptedException
final void wait() throws InterruptedException
- Blocked on I/O ? The thread waits for
completion of blocking operation. A thread can enter on this state because
of waiting I/O resource. In that case the thread sends back to runnable
state after availability of resources.
- Blocked for joint completion ? The thread
can come on this state because of waiting the completion of another thread.
- Blocked for lock acquisition ? The thread can come on this state because of waiting to acquire the lock of an object.
Methods that can be applied apply on a Thread:
Some Important Methods defined in java.lang.Thread are shown in the table:
| Method | Return Type | Description |
| currentThread( ) | Thread | Returns an object reference to the thread in which it is invoked. |
| getName( ) | String | Retrieve the name of the thread object or instance. |
| start( ) | void | Start the thread by calling its run method. |
| run( ) | void | This method is the entry point to execute thread, like the main method for applications. |
| sleep( ) | void | Suspends a thread for a specified amount of time (in milliseconds). |
| isAlive( ) | boolean | This method is used to determine the thread is running or not. |
| activeCount( ) | int | This method returns the number of active threads in a particular thread group and all its subgroups. |
| interrupt( ) | void | The method interrupt the threads on which it is invoked. |
| yield( ) | void | By invoking this method the current thread pause its execution temporarily and allow other threads to execute. |
| join( ) | void | This method and join(long millisec) Throws InterruptedException. These two methods are invoked on a thread. These are not returned until either the thread has completed or it is timed out respectively. |