Java Multi-Thread多线程 - Andy's Blog

Multi - threading is the ability to execute multiple different paths of code at the same time. Java program normally only use one thread.

Ways of creating a new thread

Next to the main class, create a new class (any name you like).

1. A class extends the thread class.

   At the end of the new class add extends Thread.

   
   

   MultiThread.java

   public class MultiThread extends Thread
   {
       private int threadNum;
   
       public MultiThread(int threadNum)
       {
           this.threadNum = threadNum;
       }
   
       @Override
       public void run()
       {
           for (int i = 0; i <= 5; i++)
           {
               System.out.println(i + " from thread " + threadNum);
   
               /* test of multi-thread
               if (threadNum == 3)
               {
                   throw new RuntimeException();
               }
               */
   
               try
               {
                   Thread.sleep(1000);
               }
               catch (InterruptedException e)
               {
                   e.printStackTrace();
               }
           }
       }
   }

   
   

   Main.java

   public class Main
   {
       public static void main(String[] args)
       {
           for (int i = 0; i <= 3; i++)
           {
               MultiThread thread = new MultiThread(i);
               thread.start();
           }
           // Multi-thread test
           //throw new RuntimeException();
       }
   }

   
   
   

2. A class implements the Runnable interface.

   At the end of the new class add implements Runnable.

MultiThread.java

public class MultiThreadTest implements Runnable
{
    private int threadNum;
    public MultiThreadTest(int threadNum)
    {
        this.threadNum = threadNum;
    }

    @Override
    public void run()
    {
        for (int i = 0; i <= 5; i++)
        {
            System.out.println(i + " from thread " + threadNum);

            /*
            if (threadNum == 3)
            {
                throw new RuntimeException();
            }
            */

            try
            {
                Thread.sleep(1000);
            }
            catch (InterruptedException e)
            {
                e.printStackTrace();
            }
        }
    }
}

Main.java

for (int i = 0; i <= 3; i++)
        {
            MultiThreadTest thread = new MultiThreadTest(i);
            Thread mythread = new Thread(thread);
            mythread.start();

            /* join会在启动下一个线程前等待当前线程完成 --> 不会是多线程
            try {
                mythread.join();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            */

            // 判断当前线程是否在运行
            //mythread.isAlive();
        }
		// Multi-thread test
        //throw new RuntimeException();

Differences & pros/cons between using extends or implements here

If we are using extends, which means the new class we create CAN NOT inherent from other classes anymore. Because in Java, we are not allow multi-inheritance which means each sub-class CAN ONLY HAVE ONE super class. If we are using extends then we have no chance to let that new class to inherent from other class.

But implements are different, a sub-class can only have one super class but it can have multiple interfaces. We can implements more than one interfaces if we like. By using implements Runnable to create a new thread we are still be able to extends that new class to some other super class.

Reference

• Multithreading in Java Explained in 10 Minutes