New to Java

Hi im stucked with my assignment. Its simple bank with bank accounts. I have to implement BankTester where i have to connect those two classes with do-while loop.

Using do-while loop ask a user to enter an accountNumber and a balance and passes them to the method addAccount to add a new BankAccount to the bank. After that asks a user to make one withdrawal and one deposit for the just created account.

This is what i did so far...

Bank.java

import java.util.ArrayList;

/**
   This bank contains a collection of bank accounts.
*/
public class Bank
{   

/**
      Constructs a bank with no bank accounts.
   */
   public Bank()
   {
      accounts = new ArrayList<BankAccount>();
   }
   
   
   public void addAccount(int aNumber, double aBalance, BankAccount a)
   {
      accounts.add(a);
   }
   
   
   /**
   Finds a bank account with a given number.
   @param aNumber the number to find
   @return the account with the given number, or null if there
   is no such account
*/
public BankAccount find(int aNumber)
{
   for (BankAccount a : accounts)
   {
      if (a.getAccountNumber() == aNumber) // Found a match
         return a;
   } 
   return null; // No match in the entire array list
}
/**
Gets the bank account with the largest balance.
@return the account with the largest balance, or null if the
bank has no accounts
*/
public BankAccount getMaximum()
{
   if (accounts.size() == 0) return null;
   BankAccount largestYet = accounts.get(0);
   for (int i = 1; i < accounts.size(); i++) 
   {
      BankAccount a = accounts.get(i);
      if (a.getBalance() > largestYet.getBalance())
         largestYet = a;
   }
   return largestYet;
}   

/**
Gets the bank account with the smallest balance.
@return the account with the largest balance, or null if the
bank has no accounts
*/
public BankAccount getMinimum()
{
   if (accounts.size() == 0) return null;
   BankAccount smallestYet = accounts.get(0);
   for (int i = 1; i > accounts.size(); i++) 
   {
      BankAccount b = accounts.get(i);
      if (b.getBalance() < smallestYet.getBalance())
         smallestYet = b;
   }
   return smallestYet;
}   
   
   private ArrayList<BankAccount> accounts;

   
}

BankAccount.java

import java.util.ArrayList;
/**
   A bank account has a balance that can be changed by 
   deposits and withdrawals.
*/
public class BankAccount
{  


/**
      Constructs a bank account with a zero balance
      @param anAccountNumber the account number for this account
   */
   public BankAccount(int anAccountNumber)
   {   
	  accountNumber = anAccountNumber; 
      balance = 0;
      transactions = new ArrayList<Double>();
   }
   
   public void addTransaction(Double a)
   {
      transactions.add(a);
   }
   /**
      Constructs a bank account with a given balance
      @param Number the account number for this account
      @param initialBalance the initial balance
   */
   public BankAccount(int anAccountNumber, double initBalance)
   {   
      accountNumber = anAccountNumber;
      balance = initBalance;
      transactions.add(balance);    
   }

   /**
      Gets the account number of this bank account.
      @return the account number
   */
   public int getAccountNumber()
   {   
      return accountNumber;
   }
   /**
   Gets the current balance of the bank account.
   @return the current balance
*/
   public double getBalance()
   {   
   return balance;
   }


   /**
      Deposits money into the bank account.
      @param amount the amount to deposit
   */
   public void deposit(double amount)
   {  
      double newBalance = balance + amount;
      balance = newBalance;
      transactions.add(amount);
   }

   /**
      Withdraws money from the bank account.
      @param amount the amount to withdraw
   */
   public void withdraw(double amount)
   {   
      double newBalance = balance - amount;
      balance = newBalance;
      transactions.add(-amount);
   }
   
   public double getAverageTransaction()
   {
      double total = 0;
      for (Double a : transactions)
      {
         total = total + getBalance();
      }
      
      return total / transactions.size();		   
   }
   
   private int accountNumber;
   private double balance;
   private ArrayList<Double> transactions;
}

Heres tester

import javax.swing.JOptionPane;


public class BankTester {
	
	public static void main(String[] args)
	   {
	      String accnumber = JOptionPane.showInputDialog("Please enter your account number:");
	      
	      int accountNumber = Integer.parseInt(accnumber); 
	      
	      String abalance = JOptionPane.showInputDialog("Please enter your account balance:");
	      
	      double balance = Integer.parseInt(abalance); 
	      
	      Bank firstBankOfJava = new Bank();
	      firstBankOfJava.addAccount(new BankAccount(accnumber, abalance));
	    
	   }
}

Thanks for any help or tips!