// SavingsAccount: handle balance and operations
public class SavingsAccount {
  // private data (instance variables) here
  private double myCurrentBalance;
  private double myInterest;
 
  // Constructors
  // Constructs a savings account with a zero balance./
  public SavingsAccount() {
    // initialize instance variables to 0
    this(0.0, 0.0);
  }
  
  // Constructs a savings account with a given balance
  //    @param initialBalance the initial balance
  public SavingsAccount(double initialBalance, 
                        double initialInterest) {
    // initialize 
    myCurrentBalance = initialBalance;
    myInterest = initialInterest;
  }
 
  // methods
  // add interest into the savings account.
  public void addInterest(){
    //  Add interest to balance
    double interestAmount = myCurrentBalance*myInterest;
    myCurrentBalance = myCurrentBalance + interestAmount;
  }

  // Deposits money into the savings account.
  //    @param amount the amount to deposit
  public void deposit(double amount){
    //  Add amount to balance
    myCurrentBalance = myCurrentBalance + amount;
  }
 
  // Withdraws money from the savings account
  //    @param amount the amount to withdraw
  public void withdraw(double amount){
    //  Subtract amount from balance
    myCurrentBalance = myCurrentBalance - amount;
  }
 
  // Gets the current balance of the savings account.
  //    @return the current balance
  public double getBalance(){
    //  Return balance
    return myCurrentBalance;  
  }
  
  // Gets the interest rate of the savings account.
  //    @return the interest
  public double getInterest(){
    //  Return interest rate
    return myInterest;  
  }
 
  // toString method allows printing class instance
  public String toString() {
    return "Current Balance: " + myCurrentBalance +
       ", Interest Rate: " + myInterest;
  }
}

public class SavingsAccountTest {

   public static void main(String[] args) {
      SavingsAccount savings1 = 
         new SavingsAccount(1000, 0.10);
      System.out.println("Savings 1 balance: " +
         savings1.getBalance());
      savings1.addInterest();
      savings1.addInterest();
      savings1.addInterest();
      System.out.println("Savings 1 balance: " +
         savings1.getBalance());
      savings1.addInterest();
      savings1.addInterest();
      savings1.addInterest();
      System.out.println("Savings 1 balance: " +
         savings1.getBalance());
      System.out.println("Savings 1 interest: " +
         savings1.getInterest());
      // call toString method implicitly
      System.out.println(savings1);
      
      SavingsAccount savings2 = 
         new SavingsAccount();
      System.out.println(savings2);
   }
}

Output:
Savings 1 balance: 1000.0
Savings 1 balance: 1331.0    (After 3 years)
Savings 1 balance: 1771.561  (After 3 more years)
Savings 1 interest: 0.1
(Final balance for savings1 account)
Current Balance: 1771.561, Interest Rate: 0.1
(Balance and interest for savings2 account)
Current Balance: 0.0, Interest Rate: 0.0