Introduction to Java Threads: Creation, States, and Examples

回答：

Java threads are a fundamental part of Java's concurrency model, allowing multiple threads to run concurrently within a single program. A thread is essentially a lightweight process that can execute code independently. Java provides built-in support for multithreading, enabling developers to create applications that can perform multiple tasks simultaneously, improving performance and responsiveness.

Key Concepts of Java Threads

Thread Creation: In Java, threads can be created in two primary ways:
- By extending the Thread class.
- By implementing the Runnable interface.
Thread States: A thread can be in one of several states:
- New: The thread is created but not yet started.
- Runnable: The thread is ready to run and waiting for CPU time.
- Blocked: The thread is blocked waiting for a monitor lock.
- Waiting: The thread is waiting indefinitely for another thread to perform a particular action.
- Timed Waiting: The thread is waiting for another thread to perform an action for up to a specified waiting time.
- Terminated: The thread has completed its execution.
Synchronization: To prevent thread interference and ensure data consistency, Java provides synchronization mechanisms, such as synchronized methods and blocks.
Thread Lifecycle: The lifecycle of a thread includes states like New, Runnable, Blocked, Waiting, Timed Waiting, and Terminated, which are managed by the Java Virtual Machine (JVM).

Example 1: Creating a Thread by Extending the Thread Class

class MyThread extends Thread {
    public void run() {
        for (int i = 0; i < 5; i++) {
            System.out.println(Thread.currentThread().getName() + " - Count: " + i);
            try {
                Thread.sleep(500); // Sleep for 500 milliseconds
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}

public class ThreadExample {
    public static void main(String[] args) {
        MyThread thread1 = new MyThread();
        MyThread thread2 = new MyThread();
        
        thread1.start(); // Start thread1
        thread2.start(); // Start thread2
    }
}

Example 2: Creating a Thread by Implementing the Runnable Interface

class MyRunnable implements Runnable {
    public void run() {
        for (int i = 0; i < 5; i++) {
            System.out.println(Thread.currentThread().getName() + " - Count: " + i);
            try {
                Thread.sleep(500); // Sleep for 500 milliseconds
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}

public class RunnableExample {
    public static void main(String[] args) {
        Thread thread1 = new Thread(new MyRunnable());
        Thread thread2 = new Thread(new MyRunnable());
        
        thread1.start(); // Start thread1
        thread2.start(); // Start thread2
    }
}

Example 3: Synchronization

class Counter {
    private int count = 0;

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

    public int getCount() {
        return count;
    }
}

class CounterThread extends Thread {
    private Counter counter;

    public CounterThread(Counter counter) {
        this.counter = counter;
    }

    public void run() {
        for (int i = 0; i < 1000; i++) {
            counter.increment();
        }
    }
}

public class SyncExample {
    public static void main(String[] args) throws InterruptedException {
        Counter counter = new Counter();
        Thread thread1 = new CounterThread(counter);
        Thread thread2 = new CounterThread(counter);
        
        thread1.start();
        thread2.start();
        
        thread1.join(); // Wait for thread1 to finish
        thread2.join(); // Wait for thread2 to finish
        
        System.out.println("Final Count: " + counter.getCount());
    }
}

Summary