Java和命令行参数中的线程

Question

So I am writing a simple thread to add two vectors together and it takes 2 command line arguments: vector length and number of threads. From what I understand, the program is supposed to take in these two arguments and add up the vectors according to them showing the performance depending on the number of threads and vector length. This is where I am stuck. So far I have written basic code that adds two vectors together using arrays and creates the threads, showing the times but I am having trouble implementing it with the command line arguments. Here is what I've done so far.

      public class Addition 
      {

         public static void main(String args[])
         {
        int NoOfThreads = Integer.parseInt(args[0]);
        VectorLength = Integer.parseInt(args[1]);

        System.out.println("Start time: " + System.nanoTime());//print start time
        Thread v1 = new Vector();
        Thread v2 = new Vector();
        Thread vsum = new Vector();


        //start all threads
        v1.start();    
        v2.start();    
        vsum.start();
        //vsum2.start();
        System.out.println("End time: " + System.nanoTime());//print end time
     }

  }

  public class Vector extends Thread
  {    


//create vectors and assign them arbitrary values
int v1[] = {12,13,14,15,16,17,18}; 
int v2[] = {15,19,20,22,24,26,28};

//initialise the vector sums to zero
int vsum = 0;
public void run()
{
        //loop to add up the elements of the first vector
        if(Integer.parseInt(args[0])> 0 )
        {
            for(int i = 0; i < v1.length; i++)
            {
                 for(int j=0; j<v2.length; j++)
                 {       
                    vsum = v1[i]+ v2[j];
                    System.out.println("Current total of vector 1: " + vsum);
                    try
                    {
                        System.out.println(System.nanoTime());
                        Thread.sleep(100);
                    }
                    catch (InterruptedException e)
                       {}           
                 }//for
            }

        }
}

}

Answer 1

You cannot use args outside the main class.
Please don't use Vector as it is an implementation of ArrayList .
What you can do is add member variable to your thread class as int NoOfThreads and set it while constructing the thread class and use this in your run() .

Answer 2

A few notes:

1. Your addition code uses a nested loop. I assume that wasn't the intention. In order to sum two vectors one loop is enough.
2. In main(..) , you are not waiting properly for the threads to terminate. "End time:..." will be printed immediately after you start the threads. Use Thread.join() .
3. You are not using the number of threads in the input. You always create and start 3 threads. Same with the vector length. It's not passed down to the threads.
4. Consider adding some unique id per thread, so that you can distinguish between them when they print to the console.
5. As others mentioned, the code doesn't even compile. Make it compile first ( vectorLength not declared, args unknown in the scope where it's used, etc.)

Answer 3

I see two compilation problems here.

Firstly, the type of VectorLength isn't defined. I think it should be int VectorLength .

Secondly, you are trying to access args reference in the Vector class which does not seem available.

If you want to use args in the Vector class, you can pass this as an argument to Vector constructor and store it as a field. Something like this:

public Vector(String[] args) {
    this.args = args;
}

And from your Addition class you should then be using this overloaded constructor:

Thread v1 = new Vector(args);
Thread v2 = new Vector(args);

Answer 4

Creating a class as Vector will not be a problem since Vector is not a reserved keyword in Java and since you are not using the Vector Class of <>-><> it will not be a problem.

The only problem i can see is in this code

int NoOfThreads = Integer.parseInt(args[0]);
VectorLength = Integer.parseInt(args[1]);

You are trying to initialize two variable NoOfThreads and VectorLength at the same time but have ended the statement in between with a semicolon.

int NoOfThreads = Integer.parseInt(args[0])**,**
    VectorLength = Integer.parseInt(args[1]);

notice the comma inplace of semicolon.

Secondly, you are trying to access args[0] in the run method in Vector class but the scope of args array is in the main method of the Addition.

if(Integer.parseInt(args[0])> 0 )

Try solving both problems on your own. All the best.

Answer 5

There are too many things broken in your code. Here are few.

1. You are using args outside of main. (set it as a attribute of Vector class and initialize it during object creation)
2. Vector works fine but it would make sense to use a different class name
3. You can have only one public class in a file. (Put Vector in a different file or remove public)
4. Why do you need the vector size and thread count from commmand line? Your vector size and tread count is static (pre-defined).
5. If you are trying to dynamically create a vector from the given size and also run threads from the thread size then there are lot of changes that needs to be made to your code.

I would suggest to begin on more humble programming exercises before going for this task.