Need some help with Java program Airline.java

[carl martin]

I am new to Java, and I have been using a book to learn it myself. I have hit a few snags, but have gotten through most of them without too much of an issue. I just came upon a problem int he book that I am stumped on. I am getting errors, and I am not really sure I am even doing this right. Please help me out.

QUESTION IN THE BOOK:

Write an airline ticket reservation program called airline.java. The program should display a menu with the following options: reserve a ticket, cancel a reservation, check whether a ticket is reserved for a particular person, and display the passengers. The information is maintained on an alphabetized linked list of names. Assume that tickets are reserved for only one flight. Create a linked list of flights with each node including a reference to a linked list of passengers.

ERRORS:

Airline.java:68: cannot find symbol
symbol : variable valid
location: class Airline.Console
valid = true;
^
Airline.java:146: non-static method readInt() cannot be referenced from a static context
choice = Console.readInt();
^
Airline.java:230: non-static method readString() cannot be referenced from a static context
return Console.readString();
^
Airline.java:243: non-static method readInt() cannot be referenced from a static context
seat = Console.readInt();
^
4 errors


CODE

import java.io.*;
import java.util.*;

public class Airline {

	/**
	 * The number of seats on the plane
	 */
	static final int MAX_SEATS = 8;

public Airline() {
    }

	public void main(String[] args) {

		boolean done = false;

		String[] seats = new String[MAX_SEATS];		// the passenger list
		initializeSeats(seats);

		do {
			printMainMenu();
			int choice = getMainMenuChoice();		// choice off of the main menu

			switch (choice) {
			case 1:
				makeReservation(seats);
				break;
			case 2:
				cancelReservation(seats);
				break;
			case 3:
				printSeatingChart(seats);
				break;
			case 4:
				done = true;
				break;
			}

		} while (!done);

	}

//CONSOLE
public class Console {

	private  BufferedReader in;
	private  String integerReprompt = "Invalid integer. Try again: ";
	private  String doubleReprompt = "Invalid double. Try again: ";
	private  String charReprompt = "Invalid character. Try again: ";

	 {

		in = new BufferedReader(new InputStreamReader(System.in));
	}

	public String readString() {
		String s = null;
			s = in.readLine();
		return s;
	}

	public char readChar() {
		char c = 0;
			String s = in.readLine();
				if (s.length() == 1) {
					c = s.charAt(0);
					valid = true;
				} else {
					System.out.print(charReprompt);
				}
		return c;
	}

	int readInt() {
		int i = 0;

			boolean valid = false;

					i = Integer.parseInt(in.readLine());
					valid = true;

					System.out.print(integerReprompt);

		return i;
	}

	public double readDouble() {
		double d = 0.0;

		boolean valid = true;

					d = Double.parseDouble(in.readLine());
					valid = true;
					valid = false;
					System.out.print(doubleReprompt);


		return d;
	}

	public void pause() {
			System.out.print("Press enter to continue...");
			in.readLine();
		}

	public void setIntegerReprompt(String prompt) {
		integerReprompt = prompt;
	}

	public void setDoubleReprompt(String prompt) {
		doubleReprompt = prompt;
	}

	public void setCharReprompt(String prompt) {
		charReprompt = prompt;
	}

}
//END CONSOLE




	/**
	 * Print the main menu
	 */
	void printMainMenu() {
		System.out.println("\nMain Menu\n");
		System.out.println("1. Make a reservation");
		System.out.println("2. Cancel a reservation");
		System.out.println("3. Print seating chart");
		System.out.println("4. Quit");
		System.out.println();
	}

	/**
	 * Get the user's choice off the main menu
	 */
	int getMainMenuChoice() {
		int choice;				// choice entered
		boolean valid = false;	// is choice valid?

		do {
			System.out.print("===> ");
			choice = Console.readInt();

			if (1 <= choice && choice <= 4) {
				valid = true;
			} else {
				System.out.println("Invalid choice.");
			}
		} while (!valid);

		return choice;
	}

	/**
	 * Initialize each element of seats to the empty string
	 */
	void initializeSeats(String[] seats) {
		for (int i = 0; i < seats.length; i++) {
			seats[i] = "";
		}
	}

	/**
	 * Make a reservation
	 */
	void makeReservation(String[] seats) {
		int seatIndex = findEmptySeat(seats);	// index of first empty seat
		if (seatIndex == seats.length) {
			System.out.println("All seats are full. Sorry.");
		} else {
			String name = getPassengerName();	// passenger's name
			seats[seatIndex] = name;
			System.out.println(name + " has been assigned seat #" + (seatIndex+1));
		}
	}

	/**
	 * Cancel a reservation
	 */
	void cancelReservation(String[] seats) {
		int seatIndex = getSeatToCancel();		// index of seat to cancel reservation for
		if (isEmpty(seats, seatIndex)) {
			System.out.println("Seat #" + (seatIndex+1) + " has not been reserved for anyone");
		} else {
			seats[seatIndex] = "";
			System.out.println("Seat #" + (seatIndex+1) + " is now available");
		}
	}

	/**
	 * Print the seating chart
	 */
	void printSeatingChart(String[] seats) {
		System.out.println("\nSeating Chart\n");
		for (int i = 0; i < seats.length; i++) {
			System.out.println((i+1) + ". " + seats[i]);
		}
	}

	/**
	 * Find the index of the first empty seat on the plane.
	 * If there are no empty seats, return seats.length
	 */
	int findEmptySeat(String[] seats) {
		for (int i = 0; i < seats.length; i++) {
			if (isEmpty(seats, i)) {
				return i;
			}
		}

		return seats.length;
	}

	/**
	 * Yield whether seats[seatIndex] is an empty seat.
	 */
	boolean isEmpty(String[] seats, int seatIndex) {
		return seats[seatIndex].equals("");
	}

	/**
	 * Input a passenger's name
	 */
	String getPassengerName() {
		System.out.print("Enter the passenger's name: ");
		return Console.readString();
	}

	/**
	 * Input the number of a seat to cancel, return the
	 * index of that seat.
	 */
	int getSeatToCancel() {
		boolean valid = false;	// is the seat number valid?
		int seat;				// seat number to cancel

		do {
			System.out.print("Enter the seat to cancel: ");
			seat = Console.readInt();
			if (1 <= seat && seat <= MAX_SEATS) {
				valid = true;
			} else {
				System.out.println("Invalid seat number");
			}
		} while (!valid);

		return seat-1;
	}

}

[Ernest Friedman-Hill]

Hi,

Welcome to JavaRanch!

There are really only two problems here: the first one and the other three. In the first one, there's no variable "valid" that's in scope for that method (readChar()). All the other "valid" variables are declared inside methods (like in readInt()) so they're available only inside those methods. Is there just one line of code that you forgot to type? Do you understand what "scope" is?

For the other three compile errors: you need an instance of the Console class to call its non-static methods (i.e., new Console()), or the methods would have to be declared "static". Do you know what static methods are?

[Janeice DelVecchio]

carl martin wrote:
ERRORS:

Airline.java:68: cannot find symbol
symbol : variable valid
location: class Airline.Console
valid = true;

Do you know what this error means? It means you're using a variable that hasn't been locally declared....
Let's look around line 68....

    public char readChar() {   
        char c = 0;   
            String s = in.readLine();   
                if (s.length() == 1) {   
                    c = s.charAt(0);   
                    valid = true;     // this 'valid' hasn't been declared in this method.
                } else {   
                    System.out.print(charReprompt);   
                }   
        return c;   
    }       

I'm assuming valid should be a boolean? declare it as such, and that should get rid of your first error.

As for the "non-static method readInt() cannot be referenced from a static context"
well, the main method is static. It's trying to call methods that are non static. If you make those methods static, the error will go away.

EDIT: EFH beat me cause I type slow

[carl martin]

Thanks everyone. I was just wicked tired of working on that and needed a break. With your help I have those errors fixed, and the program is ALMOST working now.

[Campbell Ritchie]

You can't get new Console(); you have to use a method of the System class which returns the Console, but I can't remember its name just at the moment.

Beware of Console; if you open the application with "javaw" as you do for an executable .jar, you don't get a Console at all, and any attempt to use it results in a NullPointerException.

[Christophe Verré]

Campbell Ritchie wrote:You can't get new Console(); you have to use a method of the System class which returns the Console, but I can't remember its name just at the moment.

System.console().

[Ernest Friedman-Hill]

Christophe Verré wrote:

Campbell Ritchie wrote:You can't get new Console(); you have to use a method of the System class which returns the Console, but I can't remember its name just at the moment.

System.console().

Well, yeah, if he hadn't defined his own class named "Console" to which I was referring.

[Campbell Ritchie]

Sorry for the misunderstanding, Ernest.