多线程是一种Java功能，允许并发执行程序的两个或多个部分，以最大限度地利用CPU。这种程序的每个部分都称为线程。因此，线程是一个过程中的轻量级进程。
可以使用两种机制创建线程：
创建线程我们创建一个扩展java.lang.Thread类的类。此类重写Thread类中可用的run（）方法。线程在run（）方法中开始生命。我们创建了一个新类的对象，并调用start（）方法来开始执行一个线程。Start（）调用Thread对象上的run（）方法。
// Java code for thread creation by extending
// the Thread class
class MultithreadingDemo extends Thread
{
public void run()
{
try
{
// Displaying the thread that is running
System.out.println ("Thread " +
Thread.currentThread().getId() +
" is running");
}
catch (Exception e)
{
// Throwing an exception
System.out.println ("Exception is caught");
}
}
}
// Main Class
public class Multithread
{
public static void main(String[] args)
{
int n = 8; // Number of threads
for (int i=0; i<8; i++)
{
MultithreadingDemo object = new MultithreadingDemo();
object.start();
}
}
}
输出：
Thread 8 is running Thread 9 is running Thread 10 is running Thread 11 is running Thread 12 is running Thread 13 is running Thread 14 is running Thread 15 is running
创建线程我们创建了一个新类，它实现了java.lang.Runnable接口并覆盖了run（）方法。然后我们实例化一个Thread对象并在该对象上调用start（）方法。
// Java code for thread creation by implementing
// the Runnable Interface
class MultithreadingDemo implements Runnable
{
public void run()
{
try
{
// Displaying the thread that is running
System.out.println ("Thread " +
Thread.currentThread().getId() +
" is running");
}
catch (Exception e)
{
// Throwing an exception
System.out.println ("Exception is caught");
}
}
}
// Main Class
class Multithread
{
public static void main(String[] args)
{
int n = 8; // Number of threads
for (int i=0; i<8; i++)
{
Thread object = new Thread(new MultithreadingDemo());
object.start();
}
}
}
输出：
Thread 8 is running Thread 9 is running Thread 10 is running Thread 11 is running Thread 12 is running Thread 13 is running Thread 14 is running Thread 15 is running
1.如果我们扩展Thread类，我们的类不能扩展任何其他类，因为Java不支持多重继承。但是，如果我们实现Runnable接口，我们的类仍然可以扩展其他基类。
2.我们可以通过扩展Thread类来实现线程的基本功能，因为它提供了一些内置的方法，如yield()，interrupt()等在Runnable接口中不可用。
原文：https://www.cnblogs.com/breakyizhan/p/13238122.html