Trying to assign value to array elements and return it in another class to work with but not working

Question

I am having diffculty with trying to assign value to array elements based on a userinput and checking the array element's value in another class. When I do that I get null and I am not sure why and how to fix it.

I have no expereince with java, just started learning it and doing it as part of uni course.

Any help is appreciated and thank you.

Class 1

  public class ErrorHandling {
        String[] errorMessage = new String[4];

        public void inputCheck() {

            UserInterface input = new UserInterface();

            int[] checkUserInput = input.getInput();

            if (checkUserInput[0] < 20 || checkUserInput[0] > 80) {

                errorMessage[0] = "Hello";

            }

            if (!(checkUserInput[1] <= 10 && checkUserInput[1] % 2 == 0)) {

                errorMessage[2] = "Hey";
            }

        }

        public String[] getError() {
            return errorMessage;
        }
    }

Class 2

public class MainProgram {
    public static void main(String[] args) {
        UserInterface input = new UserInterface();

        input.askZigZag();

        ErrorHandling checkError = new ErrorHandling();

        String check[] = checkError.getError();

     if (check[0] == ("Hello")) {
         System.out.println("yh");
     }
    }

}

Answer 1

I think you're confusing your method calls a bit. In class 2, you have a line:

String check[] = input.getError();

That should probably be:

String check[] = checkError.getError();

As the getError() method is in your first class (ErrorHandling) and not the UserInterface class.

Also, you assign Hello to errorMessage[0] and not hey , so that might be failing in your last few lines in class 2.

If you're just starting out with Java I recommend reading up on Class Structure to understand this (as well as Arrays ).

**EDIT

String comparison in Java doesn't work using the == operator. As they are objects and not primitive data types, you must use .equals .

check[0].equals("Hello")

Answer 2

Invoke checkError.inputCheck() in the main program otherwise errorMessage will not get initialized.

Some tweaks in your code that will help to execute:

Class 1

  public class ErrorHandling {
        String[] errorMessage = new String[4];

        public void inputCheck() {

            UserInterface input = new UserInterface();

            int[] checkUserInput = input.getInput();
            // If you want to use askZigZag... use it somewhere inside this function
            // since you have already declared the object of UserInterface.

            if (checkUserInput[0] < 20 || checkUserInput[0] > 80) {

                errorMessage[0] = "Hello";

            }

            if (!(checkUserInput[1] <= 10 && checkUserInput[1] % 2 == 0)) {

                errorMessage[2] = "Hey";
            }

        }

        public String[] getError() {
            return errorMessage;
        }
    }

Class 2

    public class MainProgram {
        public static void main(String[] args) {

          //  UserInterface input = new UserInterface();

          //  input.askZigZag();

            ErrorHandling checkError = new ErrorHandling();
            checkError.inputCheck();
            String check[] = checkError.getError();

         if (check[0].equals("Hello")) {
             System.out.println("yh");
         }
        }

}