Multithreading is the ability of a central processing unit (CPU) (or a single core in a multi-core processor) to provide multiple threads of execution concurrently, supported by the operating system. This allows a program to perform multiple tasks concurrently within a single program.

In Java, multithreading is implemented using the java.lang.Thread class and the java.lang.Runnable interface.

Here is an example of how to create and start a thread using the java.lang.Thread class:

public class MyThread extends Thread {
    public void run() {
        // code to be executed by the thread
    }
}

// create and start the thread
MyThread thread = new MyThread();
thread.start();

Here is an example of how to create and start a thread using the java.lang.Runnable interface:

public class MyRunnable implements Runnable {
    public void run() {
        // code to be executed by the thread
    }
}

// create the thread
Thread thread = new Thread(new MyRunnable());

// start the thread
thread.start();

In both examples, the run() method contains the code that will be executed by the thread.

There are several ways to control the execution of threads in Java, such as:

• thread.sleep(milliseconds): Suspends the current thread for the specified number of milliseconds.
• thread.join(): Causes the current thread to wait for the thread to complete execution.
• thread.setPriority(priority): Sets the priority of the thread.
• thread.isAlive(): Returns true if the thread is still running, and false otherwise.

It is important to note that Java provides a way to synchronize the execution of threads using the synchronized keyword and the java.util.concurrent.locks.Lock interface. This is necessary to prevent race conditions, which can occur when multiple threads try to access shared resources simultaneously.

For more information on multithreading in Java, you can refer to the official Java documentation at https://docs.oracle.com/en/java/javase/14/docs/api/java.base/java/lang/Thread.html.