How to Get the Id of a Current Running Thread in Java?
The getId() method of Thread class returns the identifier of the invoked thread. The thread ID is a positive long number generated when this thread was created. The thread ID is unique and remains unchanged during its lifetime. When a thread is terminated, this thread ID may be reused.
Java allows concurrent execution of different parts of a program with the help of threads. Multithreading in Java is achieved by extending the Thread class or implementing the Runnable Interface. Since multiple inheritance is not allowed in Java it is recommended to implement the Runnable interface for thread creation so that if required the class implementing the Runnable interface can extend some other class. In this article, we have demonstrated both the methods of creating a thread. The first approach shows thread creation by extending the Thread class and the second approach shows thread creation by implementing the Runnable Interface.
public long getId()
Return value: This method returns the ID of a thread.
Approach 1: Following are the steps to create a thread by extending the Thread class.
- ThreadDemo1 class extends the Thread class and overrides the run() method of Thread class.
- In the run() method, we use the currentThread().getName() method to get the name of the current thread that has invoked the run() method.
- We use the currentThread().getId() method to get the id of the current thread that has invoked the run() method.
- Within the main() method, two instances of the ThreadDemo1 class is created.
- t1 and t2 are two threads which invoke the start() method.
- Invoking the start() method basically invokes the run() method by default.
- join() method is used to prevent t2 from running before the completion of t1.
- As soon as t1 completes t2 begins execution.
Current Thread Name: Thread-0 Current Thread Name: Thread-1 Current Thread ID: 11 Current Thread ID: 12
Approach 2: In the second approach, the thread is created by implementing the Runnable Interface.
- ThreadDemo2 class implements the Runnable interface and overrides the run() method.
- A runnable instance of ThreadDemo2 class t is created.
- Two instances of the Thread class are created by passing the runnable instance as the first parameter and the name of the thread as the second parameter
- start() method is invoked on both the threads
- start() method invokes the run() method by default
Current Thread Name: First Thread Current Thread Name: Second Thread Current Thread ID: 11 Current Thread ID: 12
Note: The output may vary for the second approach as it is not synchronized and the threads execute concurrently. So the order in which the thread name or thread id is printed may vary. To prevent this problem we used join() method in the first approach. If the order of the printed output is to be maintained then the user can use the join() method.
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