Method to check if number is contained in ArrayList will not work, NullPointerExcepton. Can you use ArrayList method inside a constructed method? - arraylist

Question

This is a project I am working on and it is supposed to take input from the user then which is an area code then see if it is contained in a array list. My method that I have created will not work in another class and I am not sure why, it is returning a NullPointerException.
The NullPointerException is shown at this line of code: if (mountainTime.contains(input))
This is the class with methods
package finalPro;
import java.util.ArrayList;
public class Final
{
public Final()
{
input = 0;
timezone = 0;
}
public void checkIfTrue(int y)
{
input = y;
if (mountainTime.contains(input))
{
timezone = 1;
}
else
timezone = 0;
System.out.println(timezone);
}
public int getZone()
{
return timezone;
}
public ArrayList<Integer> mountainTime;
private int input;
private int timezone;
}
Here is test class
package finalPro;
import java.util.ArrayList;
import javax.swing.JOptionPane;
public class FinalLogic
{
public static void main(String[] args)
{
ArrayList<Integer> mountainTime = new ArrayList<Integer>();
mountainTime.add(480);
mountainTime.add(602);
mountainTime.add(623); //Arizona area codes
mountainTime.add(928);
mountainTime.add(520);
mountainTime.add(303);
mountainTime.add(719); //Colorado
mountainTime.add(720);
mountainTime.add(970);
mountainTime.add(406); //Montana
mountainTime.add(505); //New Mexico
mountainTime.add(575);
mountainTime.add(385);
mountainTime.add(435); //Utah
mountainTime.add(801);
mountainTime.add(307); //Wyoming
Final myMap = new Final();
{
String x = JOptionPane.showInputDialog("Please enter a number: ");
int input = Integer.parseInt(x);
myMap.checkIfTrue(input);
}
}
}

Answer 1

I hope it's not too late, I haven't done anything special to fix your code, just some movement of code,
Removed the initialization logic from class FinalLogic to Final class .(btw Final name is not really good, you might be aware final is reserved word in Java. Although your name is case sensitive but still)
package finalPro;
import javax.swing.JOptionPane;
public class FinalLogic {
public static void main(String[] args) {
Final myMap = new Final();
String x = JOptionPane.showInputDialog("Please enter a number: ");
int input = Integer.parseInt(x);
myMap.checkIfTrue(input);
}
}
And here is your class Final
package finalPro;
import java.util.ArrayList;
public class Final {
public Final() {
input = 0;
timezone = 0;
// moved all initialization logic to constructor
mountainTime = new ArrayList<>();
mountainTime.add(480);
mountainTime.add(602);
mountainTime.add(623); // Arizona area codes
mountainTime.add(928);
mountainTime.add(520);
mountainTime.add(303);
mountainTime.add(719); // Colorado
mountainTime.add(720);
mountainTime.add(970);
mountainTime.add(406); // Montana
mountainTime.add(505); // New Mexico
mountainTime.add(575);
mountainTime.add(385);
mountainTime.add(435); // Utah
mountainTime.add(801);
mountainTime.add(307); // Wyoming
}
public void checkIfTrue(int y) {
input = y;
if (mountainTime.contains(input)) {
timezone = 1;
} else
timezone = 0;
System.out.println(timezone);
}
public int getZone() {
return timezone;
}
public ArrayList<Integer> mountainTime;
private int input;
private int timezone;
}
I tried in my workspace, it gives no NPE, Hope it helps.