Java Threads

🧵 Java Threads

A thread is a lightweight subprocess and the smallest unit of execution in Java.
Java allows multithreading, i.e., executing multiple threads concurrently.

Package: java.lang
Threading helps in parallel execution, responsive programs, and better CPU utilization.

1. Benefits of Threads

Concurrency – Multiple tasks at the same time
Improved Performance – Utilizes multiple cores
Better Resource Sharing – Threads share memory within the same process
Responsive GUI – Keeps user interface responsive

🔹 2. Creating Threads

There are two ways to create threads in Java:

2.1 Using `Thread` Class

class MyThread extends Thread {
public void run() {
for(int i = 1; i <= 5; i++) {
System.out.println(Thread.currentThread().getName() + " - " + i);
}
}
}

public class ThreadExample {
public static void main(String[] args) {
MyThread t1 = new MyThread();
MyThread t2 = new MyThread();

t1.start(); // Start the thread
t2.start();
}
}

class MyThread extends Thread {

public void run() {

for(int i = 1; i <= 5; i++) {

System.out.println(Thread.currentThread().getName() + " - " + i);

}

public class ThreadExample {

public static void main(String[] args) {

MyThread t1 = new MyThread();

MyThread t2 = new MyThread();

t1.start(); // Start the thread

t2.start();

}

Override the run() method.
start() calls the thread; never call run() directly for concurrency.

2.2 Using `Runnable` Interface

class MyRunnable implements Runnable {
public void run() {
for(int i = 1; i <= 5; i++) {
System.out.println(Thread.currentThread().getName() + " - " + i);
}
}
}

public class RunnableExample {
public static void main(String[] args) {
Thread t1 = new Thread(new MyRunnable());
Thread t2 = new Thread(new MyRunnable());

t1.start();
t2.start();
}
}

class MyRunnable implements Runnable {

public void run() {

for(int i = 1; i <= 5; i++) {

System.out.println(Thread.currentThread().getName() + " - " + i);

}

public class RunnableExample {

public static void main(String[] args) {

Thread t1 = new Thread(new MyRunnable());

Thread t2 = new Thread(new MyRunnable());

t1.start();

t2.start();

}

Runnable is preferred when class already extends another class.

3. Thread Lifecycle

A thread goes through five states:

New – Thread object created
Runnable – Thread is ready to run
Running – run() method executing
Waiting/Blocked – Waiting for a resource or signal
Terminated – Execution finished

4. Thread Methods

Method	Description
`start()`	Begins thread execution, calls `run()`
`run()`	Contains code executed by thread
`sleep(ms)`	Pause thread for specified milliseconds
`join()`	Waits for thread to finish
`currentThread()`	Returns reference to current thread
`getName()` / `setName()`	Get or set thread name
`setPriority(int)` / `getPriority()`	Set or get thread priority
`isAlive()`	Checks if thread is alive

5. Example: Thread Sleep & Join

class SleepThread extends Thread {
public void run() {
for(int i = 1; i <= 5; i++) {
System.out.println(Thread.currentThread().getName() + " - " + i);
try {
Thread.sleep(500); // Sleep 0.5 seconds
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}

public class ThreadSleepJoinExample {
public static void main(String[] args) throws InterruptedException {
SleepThread t1 = new SleepThread();
SleepThread t2 = new SleepThread();

t1.start();
t1.join(); // Wait until t1 finishes

t2.start();
}
}

class SleepThread extends Thread {

public void run() {

for(int i = 1; i <= 5; i++) {

System.out.println(Thread.currentThread().getName() + " - " + i);

try {

Thread.sleep(500); // Sleep 0.5 seconds

} catch (InterruptedException e) {

e.printStackTrace();

}

public class ThreadSleepJoinExample {

public static void main(String[] args) throws InterruptedException {

SleepThread t1 = new SleepThread();

SleepThread t2 = new SleepThread();

t1.start();

t1.join(); // Wait until t1 finishes

t2.start();

}

sleep() pauses execution temporarily.
join() ensures one thread completes before another starts.

6. Synchronization (Thread Safety)

Multiple threads accessing shared data can cause race conditions.
Use synchronized keyword to make methods or blocks thread-safe:

class Counter {
private int count = 0;

public synchronized void increment() {
count++;
}

public int getCount() {
return count;
}
}

public class ThreadSyncExample {
public static void main(String[] args) throws InterruptedException {
Counter counter = new Counter();

Thread t1 = new Thread(() -> {
for(int i=0;i<1000;i++) counter.increment();
});

Thread t2 = new Thread(() -> {
for(int i=0;i<1000;i++) counter.increment();
});

t1.start();
t2.start();

t1.join();
t2.join();

System.out.println("Final Count: " + counter.getCount()); // Should be 2000
}
}

class Counter {

private int count = 0;

public synchronized void increment() {

count++;

}

public int getCount() {

return count;

}

public class ThreadSyncExample {

public static void main(String[] args) throws InterruptedException {

Counter counter = new Counter();

Thread t1 = new Thread(() -> {

for(int i=0;i<1000;i++) counter.increment();

});

Thread t2 = new Thread(() -> {

for(int i=0;i<1000;i++) counter.increment();

});

t1.start();

t2.start();

t1.join();

t2.join();

System.out.println("Final Count: " + counter.getCount()); // Should be 2000

}

Summary

Thread = smallest unit of execution in Java
Created using Thread class or Runnable interface
Lifecycle: New → Runnable → Running → Waiting/Blocked → Terminated
synchronized ensures thread safety
Methods: start(), run(), sleep(), join(), getName(), etc.

Java Threads

🧵 Java Threads

1. Benefits of Threads

🔹 2. Creating Threads

2.1 Using Thread Class

2.2 Using Runnable Interface

3. Thread Lifecycle

4. Thread Methods

5. Example: Thread Sleep & Join

6. Synchronization (Thread Safety)

Summary

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2.1 Using `Thread` Class

2.2 Using `Runnable` Interface