CODEWITHSUNDEEP
exceptionpointersnull
ZeroStream
ZeroStream

Reputation: 3

Null Pointer Exception error when calling method

i have no idea what's wrong with what i am doing. It's supposed to print all patients who visited on a specific date but it keeps on throwing the null pointer error. It happens when I call on the printPatientsOnDate method.

code on the main/UI class

public void printPatientsOnDate() throws ParseException
{
    System.out.print("Enter the date(mm-dd-yyyy): ");
    Date dt = new SimpleDateFormat("MM-dd-yyyy").parse(sc.nextLine());
    for(Patient i : app.getPatientsOnSpecDate(dt))
    {
    System.out.println(i.getName());
    }
}

code on the clinic class

public ArrayList<Patient> getPatientsOnSpecDate(Date date)
{
    ArrayList<Patient> patients = null;
    for(Patient i : patientList)
    {
      if(i.searchDates(date)!=null)
      {
        patients.add(i);
      }
    }
    return patients;
}

null pointer error code

Exception in thread "main" java.lang.NullPointerException
at pkg.Pagamutan.Clinic.UI.printPatientsOnDate(UI.java:81)

Upvotes: 0

Views: 710

Answers (1)

AllTooSir
AllTooSir

Reputation: 49352

Your ArrayList<Patient> patients reference variable is null. Currently it doesn't point to any ArrayList<Patient> object .

ArrayList<Patient> patients = null;

And when you trying to invoke .add() on that null reference it throws NullPointerException.

Thrown when an application attempts to use null in a case where an object is required.

These include:

Calling the instance method of a null object. .............

You need to instantiate an ArrayList<Patient> object before invoking .add() on it.

ArrayList<Patient> patients = new ArrayList<Patient>();

Or better use List<Patient> as the reference type :

List<Patient> patients = new ArrayList<Patient>();

Upvotes: 1

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