NullPointerException error in Runtime.getRuntime().exec

Question

I'm trying to make some processes to do one task and I use Runtime.getRuntime().exec and any process read some long number from one file then use xor operand and write in another file. Finally main process should read each long number in files has produced and xor all again. Here is my code but when I run it I get NullPointerException in line that include Subprocess[i].waitFor() == 0. Why? Thanks for any help. I know what is NullPointerException and I don't want to ask about it!

    Process[] Subprocess;
    Subprocess = new Process[processCount];
    for (int i = 0; i < processCount; i++) {
        try {
            String[] command = {"java", "-cp", pathSubProcess, "SubProcess", p, String.valueOf(i), String.valueOf(processCount), String.valueOf(size)};
            Subprocess[0] = Runtime.getRuntime().exec(command);

        } catch (IOException e) {
            System.out.println(e.getMessage());
        }
    }
    /////////////////////////////////////////////////////////////////////////
    long xor = 1;
    for (int i = 0; i < processCount; i++) {
        if(Subprocess[i].waitFor() == 0){
            xor = xor ^  pp.readFiles(i);
        }
    }

   xor = xor ^ 1;

score 2 · Accepted Answer · answered Mar 29 '18 at 08:12

2

Your problem is in your assignation:

Subprocess[0] = Runtime.getRuntime().exec(command);

You always overwrite the first element of the array.

Change that 0 to i.

answered Mar 29 '18 at 08:12

Stultuske

9,296
1
25
37

God! I'm really careless! Thank you. – Samin Heydarian Mar 29 '18 at 08:17
1

@SaminHeydarian if this fixed your issue, can you mark it as 'accepted'? that way, the question won't show up as 'unanswered' anymore – Stultuske Mar 29 '18 at 08:27
of course. done. – Samin Heydarian Mar 29 '18 at 08:36

NullPointerException error in Runtime.getRuntime().exec

1 Answers1