如何通过命令行覆盖Java程序

Question

I wrote a concurrent Mergesort code with the default setting of 5 threads and an array length of 1 000 000 and i made sure that the aplication can be started from the command line via ant start.

Now my problem is that i also have to provide a small command line handling to overwrite the maximum thread number and the array length via command parameters from the console.

The Question is how can i do that and for that do i need to edit my Main code or the build.xml or just a command like go to main, change this and that ?

Main looks like this:

public class Main {

public static void main(String[] args) throws InterruptedException {

int nThreads=5;

int[] original = new int[1000000]; 
       for (int i=0; i<original.length; i++) {
        original[i] = (int) (Math.random()*9);
    }

    Mergesorts worker = new Mergesorts(original,nThreads);
    System.out.println("ressource: 1 of 5 thread(s) used");
    Thread w = new Thread(worker);
    w.start(); 
    w.join();

    }}

and thats my build.xml file:

<?xml version="1.0" encoding="UTF-8"?>


<project default="start" name="Mergesort-compile and run">

<target name="compile">
 <javac includeantruntime="false" srcdir="./src" destdir="Mergesort" />
</target>


<target name="start" depends="compile">
    <java classname="Main">
        <classpath path="Mergesort"/>
        </java>
</target>

Answer 1

Check bellow code : Java

public class Main {

  public static void main(String[] args) throws InterruptedException {
    int nThreads;

    if (args.length <= 0) {
      nThreads = 5;  // default number of threads
    } else {
      nThreads = Integer.parseInt(args[0]); // first passed parameter value 
    }

    int[] original = new int[1000000];
    for (int i = 0; i < original.length; i++) {
      original[i] = (int) (Math.random() * 9);
    }

    Mergesorts worker = new Mergesorts(original, nThreads);
    System.out.println("ressource: 1 of 5 thread(s) used");
    Thread w = new Thread(worker);
    w.start();
    w.join();

  }
}

Ant Script :

<?xml version="1.0" encoding="UTF-8"?>


<project default="start" name="Mergesort-compile and run">

<target name="compile">
 <javac includeantruntime="false" srcdir="./src" destdir="Mergesort" />
</target>


<target name="start" depends="compile">
  <property name="nthread" value="5"/>

    <java classname="Main">
        <classpath path="Mergesort"/>
        <arg value="${nthread}" />
     </java>
</target>

Run ant script as :

ant start -Dnthread=10 

this will set number of threads as 10