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Java - Thread Life CycleJava - Creating a ThreadJava - Thread MethodsJava - Thread PriorityJava - Daemon Threads

Java - Thread Methods

📌 What You Will Learn
  • What a thread is and how it is different from a process
  • Two ways to create a thread: Thread class and Runnable interface
  • The thread life cycle (states)
  • How threads cooperate: synchronized, wait and notify
  • The modern way: Executors, Callable and lambdas

Thread Methods is a core concept of the Java language. This lesson explains Common Thread Methods and Thread Class — Constants and Important Methods with complete, runnable code examples, clear step-by-step explanations, and common mistakes to avoid with exam-style MCQs at the end.

Common Thread Methods

MethodWhat it does
start()Starts the thread (calls run() in a new thread).
run()The actual job of the thread — override this.
sleep(ms)Make the current thread wait for given milliseconds.
join()Wait for another thread to finish before continuing.
setName() / getName()Give/read a friendly name to the thread.
setPriority()Hint about importance: MIN_PRIORITY(1) to MAX_PRIORITY(10), default 5.
isAlive()true if the thread is still running.
Example01
JCode Cell
1class Demo {
2 public static void main(String[] args) throws Exception {
3 Thread t = new Thread(() -> {
4 try { Thread.sleep(200); } catch (InterruptedException e) { }
5 System.out.println("Child done");
6 });
7 t.setName("Worker-1");
8 t.setPriority(Thread.MAX_PRIORITY);
9 t.start();
10 t.join(); // main waits until t finishes
11 System.out.println("Main done");
12 }
13}
Output
Child done Main done

Thread Class — Constants and Important Methods

Priority constants

Priority is only a hint to the scheduler — a higher priority thread usually gets more chances, but it is not guaranteed.

Useful methods of the Thread class

MethodWhat it does
start()Begins the thread (calls run() in a new thread)
run()The thread's job — override it
sleep(ms)Pause the current thread for the given milliseconds
join()Wait for another thread to finish
getName() / setName()Read / give a name to the thread
getPriority() / setPriority()Read / set the priority (1 to 10)
isAlive()true if the thread is still running
currentThread()Returns the currently running thread object (static)
setDaemon(true) / isDaemon()Mark / check a background helper thread
activeCount()Number of active threads (static)
Example02
JCode Cell
1Thread.MIN_PRIORITY = 1
2Thread.NORM_PRIORITY = 5 (default)
3Thread.MAX_PRIORITY = 10

Thread Class — Constants and Important Methods

Example03
JCode Cell
1class ThreadMethods {
2 public static void main(String[] args) {
3 Thread t = Thread.currentThread();
4 System.out.println("Current thread: " + t.getName());
5 System.out.println("Priority: " + t.getPriority());
6 
7 t.setName("Main-Thread");
8 t.setPriority(Thread.MAX_PRIORITY);
9 System.out.println("Now: " + t.getName() + " priority " + t.getPriority());
10 }
11}
Output
Current thread: main Priority: 5 Now: Main-Thread priority 10
📝 Key Takeaways
  • A thread is a small unit of work; a process is a running program.
  • Create a thread by extending Thread or (better) implementing Runnable.
  • Life cycle: NEW -> RUNNABLE -> BLOCKED/WAITING/TIMED_WAITING -> TERMINATED.
  • Shared data races when many threads change it; synchronized gives a lock.
  • wait/notify let threads talk; they need the lock.
  • Deadlock = threads waiting on each other's locks; avoid by consistent lock order.
  • Real projects use Executors + Callable instead of raw threads.

🧠 Test Your Knowledge

1 Questions
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