Question

Hi there i am working on LinkedList project with Java and i have some unclear issues in my mind. for example this is my “Patient” class;

public class Patient {

private int id;
private String name;
private String lastName;
private String doctor;

private Patient next;
private Patient prev;

public Patient(int id, String name, String lastName, String doctor, Patient next, Patient prev){

    this.id = id;
    this.name = name;
    this.lastName = lastName;
    this.doctor = doctor;
    this.next = next;
    this.prev = prev;

}

and when i construct my LinkedList i create a header and tail node like this.

private Patient header = new Patient(0, null, null, null, null, null);
private Patient tail = new Patient(0, null, null ,null ,null, null);

but if i create these two nodes without new Patient(0, null, null, null, null, null); anything doesnt change. could you please explain why_?

Answer 1

You get null references when not using the new keyword. Have you tried to access and do something with Objects that aren’t instanced with the new key word?
Add a method called getName() and call it on a Patient variable before it is instanced. This will result in an “null pointer exception”