Looking at the printf method
A printf format reference page (cheat sheet)

// This class shows how to initialize an array 
// How to use the printf output formatting method
public class InitPrintfArray 
{
   public static void main( String[] args )
   {
      // initializing the array when it is created
      int[] arrayA = { 87,56,78,99,102 };

      System.out.printf( "%s%7s\n", "Index", "Value" ); // column headings
   
      // output each array element's value 
      for ( int i = 0; i < arrayA.length; i++ )
         System.out.printf( "%5d%5d\n", i, arrayA[ i ] );
   } // end main
} // end class InitPrintfArray

A "simplified" version of a bar chart by using the elements of an array as counters

// Bar graph printing program.

public class BarGraph 
{
   public static void main( String[] args )
   {
      int[] arrayA = { 0, 0, 0, 0, 0, 0, 1, 2, 4, 2, 1 };

      System.out.println( "Grade distribution:" ); 

      // for each array element, output a bar of the chart
      for ( int i = 0; i < arrayA.length; i++ ) 
      {
         // output bar label ( "00-09: ", ..., "90-99: ", "100: " )
         if ( i == 10 )
            System.out.printf( "%5d: ", 100 ); 
         else
            System.out.printf( "%02d-%02d: ", 
               i * 10, i * 10 + 9  ); 
 
         // print bar of asterisks
         for ( int stars = 0; stars < arrayA[ i ]; stars++ )
            System.out.print( "*" );

         System.out.println(); // start a new line of output
      } // end outer for
   } // end main
} // end class BarGraph

Grade distribution:
00-09:
10-19:
20-29:
30-39:
40-49:
50-59:
60-69: *
70-79: **
80-89: ****
90-99: **
100: *
Claswork/Homework:
Tracing 101: Trace the i, arrayA[i], and the output as the inner and outer loops traverse arrayA.

An ADT: Greeter

public class Greeter
{
   public String sayHello()
   {
      String message = "Hello, World!";
      return message;
   }
}

The tester class also called the driver:

public class GreeterTest
{
   public static void main(String[] args)
   {
      Greeter worldGreeter = new Greeter();
      System.out.println(worldGreeter.sayHello());
   }
}

An ADT: BankAccount

/**
   A bank account has a balance that can be changed by 
   deposits and withdrawals.
*/
public class BankAccount
{  
   private double balance;

   /**
      Constructs a bank account with a zero balance.
   */
   public BankAccount()
   {   
      balance = 0;
   }

   /**
      Constructs a bank account with a given balance.
      @param initialBalance the initial balance
   */
   public BankAccount(double initialBalance)
   {   
      balance = initialBalance;
   }

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

   /**
      Withdraws money from the bank account.
      @param amount the amount to withdraw
   */
   public void withdraw(double amount)
   {   
      balance = balance - amount;
   }

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

The driver class:

/**
   A class to test the BankAccount class.
*/
public class BankAccountTester
{
   /**
      Tests the methods of the BankAccount class.
      @param args not used
   */
   public static void main(String[] args)
   {
      BankAccount harrysChecking = new BankAccount();
      harrysChecking.deposit(2000);
      harrysChecking.withdraw(500);
      System.out.println(harrysChecking.getBalance());
      System.out.println("Expected: 1500");      
   }
}

Classwork:

1. Add a method sayGoodbye to the Greeter class.
2. Add a method refuseHelp to the Greeter class. It should return a string such as “I am sorry, Dave. I am afraid I can’t do that.”
3. Write a program that constructs a bank account, deposits $1000, withdraws $500, withdraws another $400, and then prints the remaining balance.
4. Add a method

void addInterest(double rate)

to the BankAccount class that adds interest at the given rate. For example, after the statemetns

BankAccount momsSavings = new BankAccount(1000);
momsSavings.addInterest(10); // 10% interest

the balance in momsSavings is $1,100.

Assignments:

1. Add a method sayGoodbye to the Greeter class.
2. Add a method refuseHelp to the Greeter class. It should return a string such as “I am sorry, Dave. I am afraid I can’t do that.”
3. Write a program that constructs a bank account, deposits $1000, withdraws $500, withdraws another $400, and then prints the remaining balance.
4. Add a method

void addInterest(double rate)

to the BankAccount class that adds interest at the given rate. For example, after the statemetns

BankAccount momsSavings = new BankAccount(1000);
momsSavings.addInterest(10); // 10% interest

the balance in momsSavings is $1,100.

What to turn in when you submit your work in edmodo.com:
* a. Copy and paste both programs
* b. Attach both files
* c. Output should be included in your tester/driver class as a comment
* d. Test all your code: Think of data that will force execution of all the lines of code.

Classwork:
Write a class SavingsAccount_YI that is similar to the BankAccount class, except that it has an added instance variable interest. Supply a constructor that sets both the initial balance and the interest rate. Supply a method addInterest (with no explicit parameter) that adds interest to the account. Write a tester/driver program that constructs a savings account with an initial balance of $1,000 and interest rate 10%. Then apply the addInterest method five times and print the resulting balance.

/**
   A bank account has a balance that can be changed by 
   deposits and withdrawals.
*/
public class BankAccount
{  
   private double balance;

   /**
      Constructs a bank account with a zero balance.
   */
   public BankAccount()
   {   
      balance = 0;
   }

   /**
      Constructs a bank account with a given balance.
      @param initialBalance the initial balance
   */
   public BankAccount(double initialBalance)
   {   
      balance = initialBalance;
   }

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

   /**
      Withdraws money from the bank account.
      @param amount the amount to withdraw
   */
   public void withdraw(double amount)
   {   
      balance = balance - amount;
   }

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

/**
   A class to test the BankAccount class.
*/
public class BankAccountTester
{
   /**
      Tests the methods of the BankAccount class.
      @param args not used
   */
   public static void main(String[] args)
   {
      BankAccount harrysChecking = new BankAccount();
      harrysChecking.deposit(2000);
      harrysChecking.withdraw(500);
      System.out.println(harrysChecking.getBalance());
      System.out.println("Expected: 1500");      
   }
}

Classwork:

1. Add a method sayGoodbye to the Greeter class.

2. Add a method refuseHelp to the Greeter class. It should return a string such as “I am sorry, Dave. I am afraid I can’t do that.”

3. Write a program that constructs a bank account, deposits $1000, withdraws $500, withdraws another $400, and then prints the remaining balance.

4. Add a method

void addInterest(double rate)

to the BankAccount class that adds interest at the given rate. For example, after the statemetns

BankAccount momsSavings = new BankAccount(1000);
momsSavings.addInterest(10); // 10% interest

the balance in momsSavings is $1,100.