Question

I am trying to run my Binary Search Tree, I am creating objects of type Employee in my main program which does not seem to give me problems, but when I choose to search for an item in my BST, the program is terminated.

 System.out.println("Searching the Binary Search Tree");
                        System.out.println("Enter surname to search for:");
                        String choice2 = sc.nextLine(); 
                        BinaryNode a = temp.search(choice2);
                        Employee newEmp = (Employee) a.obj;
                        if (a == null)
                            {
                                System.out.println("Not Found");
                            }
                        else
                            {
                                System.out.println(newEmp.getData());
                            }
                       break;
                    }

When the program terminates, it points to the line

Employee newEmp = (Employee) a.obj;

and the error given is, java.lang.NullPointerException: null

Could anyone tell me why this is happening please?

Answer 1

You can not access to .obj of null object.
Line should be moved after check whether a==null.

 System.out.println("Searching the Binary Search Tree");
                    System.out.println("Enter surname to search for:");
                    String choice2 = sc.nextLine(); 
                    BinaryNode a = temp.search(choice2);
                    if (a == null)
                        {
                            System.out.println("Not Found");
                        }
                    else
                        {
                            Employee newEmp = (Employee) a.obj;
                            System.out.println(newEmp.getData());
                        }
                   break;
                }