How to make a method that will have affect on multiple variables?

Question

I apologize if the question doesn't make sense. I made a bank account program that manages bank accounts and I was given an assignment that asks me to make a method that adds 3 percent interest to all bank accounts.

Here is the first part of the Account class:

public class Accounts
{
   private NumberFormat fmt = NumberFormat.getCurrencyInstance();

   private final double RATE = 0.03;  // interest rate of 3.5%

   private int acctNumber;
   private double balance;
   private String name;
   //public Accounts[] account;

   //-----------------------------------------------------------------
   //  Sets up the account by defining its owner, account number,
   //  and initial balance.
   //-----------------------------------------------------------------
   public Accounts (String owner, int account, double initial)
   {
  name = owner;
  acctNumber = account;
  balance = initial;


}

Here is the method on adding interest to a single account:

 public double addInterest ()
 {
      balance += (balance * RATE);
      return balance;
 }

Here is the method that I am working on to make multiple bank accounts gain interest:

public double addInterestAll ()

   for (int i = 0; i <= 29; i++){
       account[i].addInterestAll();
   }
   return balance;


}

The account variable above is an array that I made in the main method but because I declared the array in the main method, the compiler can't find it. I am not sure of another way for how I can make this work.

Here is the main method:

public class SixSix
{
public static void main (String []args)
{


Accounts[] account = new Accounts[30];

    account[0] = new Accounts ("Gerry Agam", 1, 1111.00);
    account[1] = new Accounts ("Jules Innes", 2, 2222.00);
    account[2] = new Accounts ("Shani Cahya", 3, 3333.00);
    account[3] = new Accounts ("Bao Shelly", 4, 4444.00);
    account[4] = new Accounts ("Sasha Ashley", 5, 5555.00);
    account[5] = new Accounts ("Özgür Mor", 6, 6666.00);
    account[6] = new Accounts ("Katlego Lashawn", 7, 7777.00);
    account[7] = new Accounts ("An Narcisse", 8, 8888.00);
    account[8] = new Accounts ("Amal Lalita", 9, 9999.00);
    account[9] = new Accounts ("Sabah Dalitso", 10, 1010.00);
    account[10] = new Accounts ("Charley Robin", 11, 1111.00);
    account[11] = new Accounts ("Jo Oluwasegun", 12, 1212.00);
    account[12] = new Accounts ("Vic Nithya", 13, 1313.00);
    account[13] = new Accounts ("Nuka Kirabo", 14, 1414.00);
    account[14] = new Accounts ("Madhu Munashe", 15, 1515.00);
    account[15] = new Accounts ("Saša Guanting", 16, 1717.00);
    account[16] = new Accounts ("Esmé Emem", 17, 1717.00);
    account[17] = new Accounts ("Ren Thoko", 18, 1818.00);
    account[18] = new Accounts ("Lei Yaroslava", 19, 1919.00);
    account[19] = new Accounts ("Xuân Seong-Hy", 20, 2020.00);
    account[20] = new Accounts ("Tu Maria", 21, 2121.00);
    account[21] = new Accounts ("Nasim Noor", 22, 2222.00);
    account[22] = new Accounts ("Chandra Morgan", 23, 2323.00);
    account[23] = new Accounts ("Camille Jie", 24, 2525.00);
    account[24] = new Accounts ("Adetokunbo Sam", 25, 2626.00);
    account[25] = new Accounts ("Makena Sothy", 26, 2726.00);
    account[26] = new Accounts ("Hanne Kit", 27, 2727.00);
    account[27] = new Accounts ("Almas Florence", 28, 2828.00);
    account[28] = new Accounts ("Yoshi Saša", 29, 2929.00);
    account[29] = new Accounts ("Cahyo Ime", 30, 3030.00);

    for (int i = 0; i <=29; i++)
        System.out.println(account[i]);
    System.out.println("Depositing $100.01 from every account and withdrawing $50.05 out of every account with fee");
    for (int i = 0; i <=29; i++){
        account[i].deposit (100.01);
        account[i].withdraw (50.05, 0.0);
    }
    System.out.println("After deposit and withdrawl");
    for (int i = 0; i <=29; i++)
        System.out.println(account[i]);
    System.out.println("Account number 30 will make invalid transactions...");

    account[29].deposit (-1000.00);
    account[29].withdraw (9999999999.00, 0.1);
    account[29].toString();

    System.out.println("Adding 3 percent interest to all accounts.");
    //account.addInterestAll(account);
}
}

In conclusion, I am not sure of how to make a method on adding interest to every account in the array. Thank you in advance

Answer 1

You just have to follow the same pattern as

for (int i = 0; i <=29; i++){
    account[i].deposit (100.01);
    account[i].withdraw (50.05, 0.0);
}

like

for (int i = 0; i <=29; i++){
    account[i].addInterest ();
}

If you want one method to do all try

static public double addInterestAll (Accounts[] accounts)

   double balance = 0.0;
   for (int i = 0; i < accounts.length; i++){
       balance += accounts[i].addInterest();
   }
   return balance;
}

Then call this code

double newBalance = addInterestAll (account);