在 Java 中负责实现线程功能的类是 java.lang.Thread 类。
继承 Thread 类实现多线程的步骤：

  1. 继承 Thread 类定义线程类。
  2. 重写 Thread 类中的 run( )方法。run( )方法也称为线程体。
  3. 实例化线程类并通过 start()方法启动线程。
package com.yqq.app12;

/**
 * @Author yqq
 * @Date 2021/11/24 00:14
 * @Version 1.0
 */
public class TestThread extends Thread{
    public TestThread(){
        System.out.println(this.getName());
    }
    @Override
    public void run() {
        System.out.println(this.getName()+"线程开始");
        for (int i = 0; i < 10; i++) {
            System.out.println(this.getName()+" "+i);
        }
        System.out.println(this.getName()+"线程结束");
    }

    public static void main(String[] args) {
        System.out.println("主线程开始");
        TestThread t1 = new TestThread();
        t1.start();
        TestThread t2 = new TestThread();
        t2.start();
        System.out.println("主线程结束");
    }
}
主线程开始
Thread-0
Thread-1
主线程结束
Thread-0线程开始
Thread-0 0
Thread-0 1
Thread-0 2
Thread-0 3
Thread-0 4
Thread-0 5
Thread-0 6
Thread-0 7
Thread-0 8
Thread-0 9
Thread-0线程结束
Thread-1线程开始
Thread-1 0
Thread-1 1
Thread-1 2
Thread-1 3
Thread-1 4
Thread-1 5
Thread-1 6
Thread-1 7
Thread-1 8
Thread-1 9
Thread-1线程结束

Process finished with exit code 0