public class BankAccount {
  private static BankAccount INSTANCE;
  /** stores balance in cents */
  private int balance;

  private BankAccount() {}

  private BankAccount(int bal) {
    this.balance = bal;
  }

  public static BankAccount getInstance() {
    if (INSTANCE == null) {
      INSTANCE = new BankAccount(0);
    }
    return INSTANCE;
  }

  public void deposit(int amount) {
    INSTANCE.balance += amount;
  }

  public void withdraw(int amount) {
    INSTANCE.balance -= amount;
  }

  public int getBalance() {
    return INSTANCE.balance;
  }
}