## BankAccount.java
public abstract class BankAccount {
  public String toString() {
    return this.getClass().toString();
  }
}

## CheckingAccount.java
public class CheckingAccount extends BankAccount {
}

## SavingsAccount.java
public class SavingsAccount extends BankAccount {
}

## Main.java
public class Main {
  public static void main(String[] args) {
    BankAccount ca = new CheckingAccount();
    BankAccount sa = new SavingsAccount();

    System.out.println(ca);
    System.out.println(sa);
  }
}