Cafeteria Prices

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/*** Cafeteria ***********************************
Ronald works in the school cafeteria. He'd like to have
a program that lets him easily type in the names of food
items, and then display the prices and add them up.
He decided to use a 2-letter abbreviation for each item,
to make it faster and easier to type in the food items.
**************************************************/

public class Cafeteria
{
  String food, more ;
  double price, total;
 
  public Cafeteria()
  {
    do                       // repeat for each new customer
    { total = 0.00;
      do                           
      {                          // repeat for each food item
        food = input("Food item");
        if( food.equals("ha") )       // hamburger
        {  price = 3.50; }
        else if (food.equals("ff"))   // french fries
        {  price = 1.75; }
        else if (food.equals("ap"))   // apple
        {  price = 0.90; }
        else if (food.equals("dr"))   // drink
        {  price = 1.40; }
        else
        {  price = 0.00; }            // unknown item
        System.out.println(food + "\t" + price);
        total = total + price;     
      } while(!food.equals(""));  // press ENTER after last item
     
      System.out.println("Total = " + total);
      more = input("Next customer (or type 'quit')");
    } while (!more.equals("quit"));
  }
 
  public static void main(String[] args)
  {  new Cafeteria(); }
 
  public String input(String prompt)
  { return javax.swing.JOptionPane.showInputDialog(null,prompt); }
}
ha    3.5
ff    1.75
dr    1.4
    0.0
Total = 6.65

String Comparisons

A String variable is an Object.  This makes it different from int and float variables, which are fundamental data types.
A fundamental type only contains data.  An Object contains both data and methods.  Methods provide a behavior that
the Object can perform.  Other methods perform data manipulations. 

Fundamental types are compared by boolean operators :  = = , != ,  > , < ,  >= , <= .  That checks the data values in the same way
that people compare numbers.   So  ( 5 < 25/4 ) is true.

We cannot use = = to compare Objects.  An Object is like a box that contains some data and methods.  When we compare Objects
by = = , we are checking whether two boxes are the same - this does NOT check the contents of the boxes.  So the following
decision does not work sensibly:

      String name = "Farmer";

   String  job = "Farmer";

   if( name == job)
   {  output("That is a coincidence");  }

Checking ( name == job ) will never be true, because they are two different variables - two different boxes.

The program shows the correct way to check for equal Strings (Strings with the same content)

   if( name.equals( job ) )

That is the correct way to check whether two String variables contain the same data.

Case-Sensitive Comparison

Java is case-sensitive.  That means it thinks that capital and small letters are different - not equal.
In most situations, people don't care about capital and small letter differences.  We can do a non-case-sensitive comparison
by using .equalsIgnoreCase, like this:

      String name = "Farmer";

   String  job = "farmer";

   if( name.equalsIgnoreCase(job) )
   {  output("That is a coincidence");  }

In this case, the computer "thinks" that JOB and NAME are equal and displays "That is a coincidence."

Practice