nullPointerException while using random Java

Question

While using random generator i get error with message

Exception in thread "main" java.lang.NullPointerException

i completely don't know why, because a lot of time it working, and then it throw exception. I have feeling like resource of generating doubles just has been exploited. I have a lot of messages on screen "psst" (pMutationChangePc is set to 0.0), and accidently it always finishing in error in first IF statement. Do you guys have some ideas how to resolve this problem, or what could be the problem? Code isn't even hard to read some checking values and printing on screen...

public void Mutation()
    {
        Random r= new Random();
            if (r.nextDouble()<mutation.pMutationChangeStrategy && mutation.pMutationChangeStrategy!=0.0)
            {
                char [] tab= {'P','C','D','K'};
                System.out.println("psst");
                this.strategy.buffor=MutationRecurtion(tab, r);
            }
            if (r.nextDouble()<mutation.pMutationChangePc)
            {
                System.out.println("Mutation");
                if (r.nextBoolean()==true)
                {
                    System.out.println("boolean");
                    this.pOfCoopMax+=mutation.parameterIncMutation;
                    this.pOfCoopMin+=mutation.parameterIncMutation;
                }
                else
                {
                    this.pOfCoopMax-=mutation.parameterIncMutation;
                    this.pOfCoopMin-=mutation.parameterIncMutation;
                }
            }   
    }

Its pretty hard to throw all code, it will be unclear, but mutation is private class, and is initialized inside of constructor of this class. As i said, i have a lot of msges "psst", but it happen after some time. — Potato, Feb 14 '19 at 10:23
Your stacktrace should show the exact line your error is happening, then one of the variables on that line is null. — matt, Feb 14 '19 at 10:26

score 1 · Answer 1 · answered Feb 14 '19 at 10:18

Pass your variable into the function

public void Mutation(Object mutation)
        {
            Random r= new Random();
                if (r.nextDouble()<mutation.pMutationChangeStrategy && mutation.pMutationChangeStrategy!=0.0)
                {
                    char [] tab= {'P','C','D','K'};
                    System.out.println("psst");
                    this.strategy.buffor=MutationRecurtion(tab, r);
                }
                if (r.nextDouble()<mutation.pMutationChangePc)
                {
                    System.out.println("Mutation");
                    if (r.nextBoolean()==true)
                    {
                        System.out.println("boolean");
                        this.pOfCoopMax+=mutation.parameterIncMutation;
                        this.pOfCoopMin+=mutation.parameterIncMutation;
                    }
                    else
                    {
                        this.pOfCoopMax-=mutation.parameterIncMutation;
                        this.pOfCoopMin-=mutation.parameterIncMutation;
                    }
                }   
        }

nullPointerException while using random Java

1 Answers1