Here is my code so far (implements a similar algorithom for Wozmon in java)

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

public class rom {
    static ArrayList<Integer> address = new ArrayList<Integer>();
    static ArrayList<Integer> old = new ArrayList<Integer>();
    static int Address;

    @SuppressWarnings("resource")
    public static String writeRom(int addr, boolean flag) throws WozmonError {
        if (flag == false) {
            Scanner data = new Scanner(System.in);
            System.out.println("Give data in integer");
            int Data = data.nextInt();
            old.add(Data);
            address.add(addr);
            Address = address.indexOf(addr);
            return "Address: " + Address + address.toString() + " Data: " + old.get(Address).toString() + old.toString();

        } else {
            return "Address: " + Address + address.toString() + " Data: " + old.get(Address).toString() + old.toString();
        }
    }

    public static void readRom(int addr /* 0000-65,535 */) throws WozmonError {

        if (addr > 65535) {
            throw new WozmonError("Wozmon could not find address: " + addr);

        } else {
            System.out.println(writeRom(addr, true));
            // System.out.println("$"+addr+":"+writeRom(addr,true));
        }
    }
}

When I use the ‘writeRom’ function twice for the same address value, it gives the final output of . Is there a way to edit the writeRom function so that it does not allow duplicate values for the address array (the old array can have duplicates)