I am currently working on a program that is working with queues and simulates a

Question

I am currently working on a program that is working with queues and simulates a grocery store line. However I am having difficulties finishing it up. My main issue is that when I run the program I get a null pointer exception and can't figure out why. Below is the code that I have:

public class GroceryStoreDriver{

public static void main(String[] args){

QueueLinkedList list = new QueueLinkedList();
int queueLength = 0;
int maxLength = 0;
int numServiced = 0;
  
  
for(int i = 0; i < 60; i++) {
int r = (int)(Math.random()*4);

if(r == 1){
Customer c = new Customer();
list.add(c);
queueLength ++;
System.out.println("New customer added!! Queue length is now: " + queueLength);
}

if(!list.isEmpty()) {
list.getFirst().decServiceTime();
}

if(list.getFirst().getServiceTime() == 0) { <------------ ******I get the exception here*****
list.remove();
queueLength --;
System.out.println("Customer serviced and removed!! Queue length is now: " + queueLength);
}

if(queueLength > maxLength) {
maxLength = queueLength;
}
System.out.println("-------------------------");
}
  
}
}

Explanation / Answer

I guess the syntax you are using for generting the radom number is wrong.

int r=(int)(Math.random*4);//starts at 0, so add 1

eg. int r=(int)(Math.random*4)+1;

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