java.lang.NumberFormatException 1 (Averaging Program)

import java.util.ArrayList;
import java.util.Iterator;
import java.util.Scanner;


class Averaging {

    private static Scanner scanner = new Scanner(System.in);
    private static int pin = 0000;
    private static ArrayList<Integer> integer = new ArrayList<Integer>();


    private static int totalSum = 0;
    private static int entries = 0;

    public static void main(String[] args) {
        System.out.print("Welcome to the Averaging Program.");
        System.out.print("To verify you made this program, please enter a 4-digit pin: ");
        int passcode = scanner.nextInt();
        verify(passcode);
    }

    private static void verify(int pass) {
        if(pass == pin) {
            System.out.printf("Password accepted.\n\nI will be asking you to input values\n");
            loopInsert();
        }
    }

    private static void loopInsert() {
        for(int i = 0; i <= 25 ; i++) {
            System.out.print("Please insert a number, or to stop, type !stop.");
            String next = scanner.next();
            if(next == "!stop") {
                System.out.print("Good. I am currently calculating right now..");
                calculate();
            } else {
                integer.add(Integer.parseInt(next));
            }
        }
    }

    private static void calculate() {
        Iterator<Integer> iter = integer.iterator();
        while(iter.hasNext()) {
            entries++;
            totalSum += iter.next();
        }
        if(!iter.hasNext()) {
            int average = (totalSum/entries);
            System.out.printf("Your average is: " + average + ". I will show you what you have input.\n");
            System.out.print(integer.toString());
            System.out.print("To start a new session, please reboot me.");
        }
    }

}