Introduction to Threads

public class MyThread extends Thread {
    @Override
    public void run() {
        System.out.println("Running in: " + Thread.currentThread().getName());
    }
}

new MyThread().start(); // start() creates a new OS thread and calls run()

Runnable task = () -> System.out.println("Task in: " + Thread.currentThread().getName());

Thread t = new Thread(task, "worker-1");
t.start();

NEW → RUNNABLE → [RUNNING] → TERMINATED
              ↕
         BLOCKED/WAITING/TIMED_WAITING

Thread t = new Thread(() -> { /* ... */ });
System.out.println(t.getState()); // NEW
t.start();
System.out.println(t.getState()); // RUNNABLE
t.join();                          // wait for completion
System.out.println(t.getState()); // TERMINATED

Thread t = new Thread(task);
t.setName("processor-1");  // useful for debugging
t.setDaemon(true);         // JVM exits even if daemon threads are running
t.setPriority(Thread.MAX_PRIORITY); // 1-10, default 5 (hint only)
t.start();                 // begin execution
t.join();                  // wait for this thread to finish
t.join(5000);              // wait max 5 seconds
t.interrupt();             // request interruption

// Check interruption
if (Thread.currentThread().isInterrupted()) {
    // clean up and stop
}

// Static methods
Thread.sleep(1000);        // pause current thread (throws InterruptedException)
Thread.yield();            // hint to scheduler to yield CPU
Thread.currentThread();    // reference to currently running thread

public void run() {
    try {
        Thread.sleep(10000);
    } catch (InterruptedException e) {
        Thread.currentThread().interrupt(); // IMPORTANT: restore interrupt flag
        return; // exit cleanly
    }
}

// UNSAFE: counter++ is not atomic (read-modify-write)
private int counter = 0;
public void increment() { counter++; } // race condition!

// SAFE: use AtomicInteger
private AtomicInteger counter = new AtomicInteger();
public void increment() { counter.incrementAndGet(); }