Java ArrayList of objects' add() method not working

Question

Im new to JAVA, and Im facing a beginer's problem, I know :-P

IN PLAIN ENGLISH => I'm trying to create an ArrayList of objects, and to add new objects in the array when required.

OK, so here is a compact version of my code

package ACP.Employee;   //created package
import java.util.ArrayList;     //imported arraylist class
import ACP.Employee.EmployeeClass;  //imported employee class of same package

public class ClientClass
{
    ArrayList<EmployeeClass> empArray = new ArrayList<EmployeeClass>(); //created a new Array List

    public static void main (String[] args)
    {
        int objcount = 0;   //variable to store objct count

        empArray.add(objcount, EmployeeClass obj);
    }
}

The IDE (Eclipse) gives me following errors on empArray.add line

• Cannot make a static reference to the non-static empArray
• EmployeeClass cannot be resolved to a variable
• Syntax error on token obj, delete this token.

I have also tried to replace that line with the following syntax,

empArray.add(new EmployeeClass());

BUT the following error remains.

• Cannot make a static reference to the non-static empArray

Kindly help out here, I have seen API Spec of ArrayList's add() method, which is following:::

void add(int index, Object element) ==>> Inserts the specified element at the specified position index in the list boolean add(Object o) ==>> Appends the specified element to the end of this list. SOURCE ( http://www.tutorialspoint.com/java/java_arraylist_class.htm )

Answer 1

There are two problems with your code.

1. You are trying to access a member of the class ClientClass from a static context (main). This is only possible if that member is static. Since empArray has no modifiers it will default to package-private which is not static. You will either have to make it accessible in a static context by declaring it static:

   static ArrayList<EmployeeClass> empArray = new ArrayList<>();
   
   or create an instance of ClientClass and access its member

    ArrayList<EmployeeClass> empArray = new ArrayList<EmployeeClass>(); public static void main(String[] args) { ClientClass t = new ClientClass(); t.empArray.add(new Employee()); } 

2. The way you are passing employees to the list to be added will not compile in java. Here is a good tutorial on how to create objects in java. In fact it seems you are new to Java, so I recommend you start on page one of the tutorials, they are very good for getting familiar with the language fast and you will be productive in no time.

Answer 2

From static method you have access only to static fields.
From not-static method you have access to all fields.
Eg

private int i = 0;
private static int j = 0;

public void increment()
{
   i++; // correct
   j++; // correct
}
public static void staticIncrement()
{
   i++; // compilation error
   j++; // correct
}  

So, in you example empArray should be static .

public class ClientClass
{
    static ArrayList<EmployeeClass> empArray = new ArrayList<EmployeeClass>(); 

    public static void main (String[] args)
    {
       int objcount = 0;   //variable to store objct count

       empArray.add(objcount, new EmployeeClass());
       empArray.add(new EmployeeClass());
    }
}