Question

I have two java classes. Schedule is the main class that uses an array of Jobs called deadline. I’m having problems putting anything in array. I have a for loop that reads data from a text file (it works fine) and inserts certain data into deadline. I not successfully creating deadline because whenever I want to start inserting into the array I get a NullPointerException. (The code below the ... obviously isn’t what I actually coded, but it is still the same situation.)

It has been a while since I’ve coded in Java, so I might be just overlooking something simple, but I’m not really sure what it could be… Thanks for any help you can give.

public class Schedule {

    private Job []deadline;
    Schedule (int n){
        Job[] deadline = new Job[n];
    }

    ...
        int n = 7;
        Schedule schedule = new Schedule(n);

        deadline[0] = new Job("A",3,40); // This line won't compile. NullPointerException
}


public class Job {

    private String name;
    private int deadline;
    private int profit;

    Job(String n, int d, int p){
        name = n;
        deadline = d;
        profit = p;
    }

}

Answer 1

You are shadowing deadline in your constructor, so you don’t initialize the class member deadline, but the local one. Change it to:

    private Job []deadline;
    Schedule (int n){
        deadline = new Job[n];
    // ^^ note - no Job[] here
    }