How do I call an ArrayList method from another class?

Question

I'm in the process of creating a text UI for an ArrayList class, and I'm trying to create the methods in the second class that call the ArrayList methods. However when I'm trying to call a method that adds an object into the ArrayList , I'm getting an error.

private void addStudent()
{
    labClass.enrollStudent();
}

I'm trying to call the method enrollStudent() from the labClass class, but it's saying

method enrollStudent cannot be applied to given types

What exactly do I need to do to call this method? It's something I haven't done before.

Here's the full source code for the same class if it's needed.

import java.util.Scanner;
import java.util.*;

public class TextUI
{

    private Scanner myScanner;
    private LabClass labClass;

    public TextUI()
    {
        myScanner = new Scanner(System.in);
        createLabClass();
    }

    public void menu()
    {
        int command = -1;
        while(command != 0)
        {
            displayMenu();
            command = getCommand();
            execute(command);
        }
    }

    public void displayMenu()
    {
        System.out.println("Select command: ");
        System.out.println("    Display Full Class Details: 1");
        System.out.println("    Add Student: 2");
        System.out.println("    Find Student by Name: 3");
        System.out.println("    Set Instructor: 4");
        System.out.println("    Set Room Mumber: 5");
        System.out.println("    Set Time and Day: 6");
        System.out.println("    Remove Student: 7");
        System.out.println("    Get Class Size: 8");
        System.out.println("    Terminate Program: 0");
    }

    private void createLabClass()
    {
        LabClass labClass = new LabClass();
    }

    private int getCommand()
    {
        System.out.print("Enter command: ");
        int command = myScanner.nextInt();
        return command;
    }

    private void execute(int command)
    {
        if(command == 0)
        {
            System.out.println("Terminating program...");
            System.exit(0);
        }
        else
        if(command == 8)
        {
            System.out.println("The class size is: " + getClassSize());
        }
    }

    private int getClassSize()
    {
        return labClass.getNumberOfStudents();
    }

    private void addStudent()
    {
        labClass.enrollStudent();
    }
}

Here's the code for LabClass.enrollStudent

/**
 * Add a student to this LabClass.
 * @param newStudent the student object to be enrolled
 */
public void enrollStudent(Student newStudent)
{
    students.add(newStudent);
}

addStudent code

private void execute(int command)
{
    if(command == 0)
    {
        System.out.println("Terminating program...");
        System.exit(0);
    }
    else if(command == 1)
    {
        labClass.getLabClass();
    } 
    else if(command == 2)
    {
        addStudent();
    }
}

Answer 1

It looks like you're overwriting your class variable labClass In your createLabClass method, remove the leading LabClass . It should look like this

private void createLabClass()
{
    labClass = new LabClass();
}

I think what is happening is that you are attempting to access labClass.enrollStudent(); from your class variable, which is never instantiated. Instead, you were instantiating a local version of it that was never used

Then, when it comes to your LabClass implementation, something like this should suffice

public class LabClass() {
    private ArrayList<Student> students = new ArrayList<>();

    public void enrollStudent(Student newStudent) {
        students.add(newStudent);
    }
}

Obviously, you may have more in your class, but without knowledge of it, I wrote it as short and simple as possible

Answer 2

So in addition to what @ Brandon & @ Denis said, it turned out that you are calling the enrollStudent method with no parameters. You need to pass in a Student object to the method. Plus, you need to declare your students' arraylist as a member variable and initialize it :

public class TextUI
{
     private List<Student> students = new ArrayList<Student>();
     private Scanner myScanner;
     private LabClass labClass;

     public TextUI()
     {
         myScanner = new Scanner(System.in);
         createLabClass();
     }
     .......
}