• Explain what a Thread is in Java.
• Use thread instance methods.

Java supports thread at the JVM level, the language level with special keywords, and has standard libraries to deal with them. Every Java program runs at least one thread. This thread is called the main thread. Over the years, Java has introduced higher level abstractions to work with threads but we will start with the fundamentals to develop a solid intuition.

In Java, each thread is an instance of the java.lang.Thread class or its subclass. Threads have a name, identifier (long), a priority, and other properties that can be accessed through the instance methods.

Let’s look at an example which prints out the different properties of the main thread.

public class Main {
    public static void main(String[] args) {
        Thread t = Thread.currentThread();

        System.out.println("Name: " + t.getName());
        System.out.println("ID: " + t.getId());
        System.out.println("Alive: " + t.isAlive());
        System.out.println("Priority: " + t.getPriority());
        System.out.println("Daemon: " + t.isDaemon());

        t.setName("custom-thread");
        System.out.println("New name: " + t.getName());
    }
}

Name: main
ID: 1
Alive: true
Priority: 5
Daemon: false
New name: custom-thread

We first store the current thread reference in the t variable and then call the various instance methods on the main thread instance.

Threads with a higher priority are executed over threads with lower priority. Daemon threads are low priority threads that can run in the background. The JVM does not wait for daemon threads before exiting.

We’ve looked at the common methods for getting information on a thread. Note that all of these methods can be run on any thread and not just the main thread.