Consider the following BankAccount class definition.

public class BankAccount {
    private double balance;
    private String accountNumber;
    
    public BankAccount(String num, double bal) {
        accountNumber = num;
        balance = bal;
    }
    
    public void transfer(double amount, BankAccount other) {
        if (amount > 0 && amount <= this.balance) {
            this.balance -= amount;
            other.balance += amount;
        }
    }
    
    public double getBalance() {
        return balance;
    }
}

Which statement best explains why the transfer method can directly access the private instance variable other.balance?