11: Using Arrays and Collections to Juggle Values in Java

Drawer Code 39 Full ASCII in Java 11: Using Arrays and Collections to Juggle Values

changes from 0 to 5 Then in Figure 11-6, you run the program a second time When the program gets data from the newly written GuestListtxt file, Room 3 is no longer vacant So this time, the program suggests Room 8 Like many other methods and constructors of its kind, the PrintStream constructor doesn t pussyfoot around with files If it can t find a GuestListtxt file, the constructor creates one and prepares to write values into it But, if a GuestListtxt file already exists, the constructor clobbers the existing file and prepares to write to a new, empty GuestListtxt file If you don t like it when files are clobbered, take precautions before calling the PrintStream constructor This is more an observation than a tip Say that you want to read data from a file named Employeestxt To do this, you make a scanner You call new Scanner(new File( Employeestxt )) If you accidentally call new Scanner( Employeestxt ) without the new File part, the call doesn t connect to your Employeestxt file But notice how you prepare to write data to a file You make a PrintStream instance by calling new PrintStream ( GuestListtxt ) You don t use new File anywhere in the call If you goof and accidentally include new File, the Java compiler becomes angry, jumps out, and bites you In Listing 11-4, the condition roomNum < 10 && guests[roomNum] != 0 can be really tricky If you move things around, and write guests[roomNum] != 0 && roomNum < 10, you can get yourself into lots of trouble For details, see this book s Web site

The Java Motel is open for business, now with improved guest registration software! The people who brought you this chapter s first section are always scratching their heads, looking for the best ways to improve their services Now, with some ideas from object-oriented programming, they ve started thinking in terms of a Room class And what, you ask, is a Room instance That s easy A Room instance has three properties the number of guests in the room, the room rate, and a smoking/nonsmoking stamp Figure 11-8 illustrates the situation

1 4 2 0 2 1 4 3 0 2 6000 6000 6000 6000 8000 8000 8000 8000 1000010000

Listing 11-5 shows the code that describes the Room class As promised, each instance of the Room class has three variables: the guests, rate, and smoking variables (A false value for the boolean variable, smoking, indicates a nonsmoking room) In addition, the entire Room class has a static variable named currency This currency object makes room rates look like dollar amounts To find out what static means, see 10

Listing 11-5:

So This is What a Room Looks Like!

import static javalangSystemout; import javautilScanner; import javatextNumberFormat; class Room { private int guests; private double rate; private boolean smoking; private static NumberFormat currency = NumberFormatgetCurrencyInstance(); public void readRoom(Scanner diskScanner) { guests = diskScannernextInt(); rate = diskScannernextDouble(); smoking = diskScannernextBoolean(); } public void writeRoom() { outprint(guests); outprint( \t ); outprint(currencyformat(rate)); outprint( \t ); outprintln(smoking yes : no ); } }

Listing 11-5 has a few interesting quirks, but I d rather not describe them until after you see all the code in action That s why, at this point, I move right on to the code that calls the Listing 11-5 code After you read about arrays of rooms (shown in Listing 11-6), check out my description of the Listing 11-5 quirks

So now you need an array of rooms The code to create such a thing is in Listing 11-6 The code reads data from the RoomListtxt file (Figure 11-9 shows the contents of the RoomListtxt file) Figure 11-10 shows a run of the code in Listing 11-6

Listing 11-6: