Why can't my main class see the array in my calender class

Question

This is a homework problem. I'm already 5 days late and can't figure out what I'm doing wrong.. this is my 1st semester in Java and my first post on this site

Here is the assignment..

Create a class called Calendar. The class should contain a variable called events that is a String array. The array should be created to hold 5 elements. Use a constant value to specify the array size. Do not hard code the array size. Initialize the array in the class constructor so that each element contains the string “ – No event planned – “.

The class should contain a method called CreateEvent. This method should accept a String argument that contains a one-word user event and an integer argument that represents the day of the week. Monday should be represented by the number 1 and Friday should be represented by the number 5. Populate the events array with the event info passed into the method. Although the user will input one-word events, each event string should prepend the following string to each event:

event_dayAppoinment: (where event_day is the day of the week)

For example, if the user enters 1 and “doctor” , the first array element should read: Monday Appointment: doctor

If the user enters 2 and “PTA” , the second array element should read: Tuesday Appointment: PTA

Write a driver program (in a separate class) that creates and calls your Calendar class. Then use a loop to gather user input. Ask for the day (as an integer) and then ask for the event (as a one word string). Pass the integer and string to the Calendar object’s CreateEvent method. The user should be able enter 0 – 5 events. If the user enters -1, the loop should exit and your application should print out all the events in a tabular format. Your program should not allow the user to enter invalid values for the day of the week. Any input other than 1 – 5 or -1 for the day of the week would be considered invalid.

Notes: When obtaining an integer from the user, you will need to use the nextInt() method on your Scanner object. When obtaining a string from a user, you will need to use the next() method on your Scanner object.

Here is my code so far..

//DRIVER CLASS

/**
 *
 * @author Rocky
 */

//imports scanner
import java.util.Scanner;

//begin class driver       
public class driver {

    /**
     * @paramargs the command line arguments
     */
    //begin main method
    public static void main(String[] args) {
        //initiates scanner
        Scanner userInput = new Scanner (System.in);

        //declare variables
        int dayOfWeek;
        String userEvent;

        //creates object for calender class
        calendercalenderObject = new calender();

        //user prompt
        System.out.println("Enter day of week for your event in the following format:");
        System.out.println("Enter 1 for Monday");
        System.out.println("Enter 2 for Tuesday");
        System.out.println("Enter 3 for Wednsday");
        System.out.println("Enter 4 for Thursday");
        System.out.println("Enter 5 for Friday");
        System.out.println("Enter -1 to quit");

        //collect user input
        dayOfWeek = userInput.nextInt(); 

        //user prompt
        System.out.println("Please type in the name of your event");

        //collect user input
        userEvent = userInput.next();

        //begin while loop
        while (dayOfWeek != -1) {
            //test for valid day of week
            if ((dayOfWeek>=1) && (dayOfWeek<=5)){
                //calls createEvent method in calender class and passes 2 variables
                calenderObject.createEvent(userEvent,dayOfWeek);
            }  else {
                //error message
                System.out.println("You have entered an invalid number");

                //user prompts
                System.out.println("Press -1 to quit or enter another day");
                System.out.println("Enter 1 for Monday");
                System.out.println("Enter 2 for Tuesday");
                System.out.println("Enter 3 for Wednsday");
                System.out.println("Enter 4 for Thursday");
                System.out.println("Enter 5 for Friday");
                System.out.println("Enter -1 to quit");

                //collect user input
                dayOfWeek = userInput.nextInt(); 

                //end data validity test
            }
            //end while loop
        }


        //prints array to screen
        int i=0;

        for (i=0;i<events.length;i++){
            System.out.println(events[i]);
        }
        //end main method
    }
}


/**
 *
 * @author Rocky
 */

//imports scanner
import java.util.Scanner;


//begin calender class
public class calender {

    //creates events array
    String[] events = new String[5];

    //begin calender class constructor
    public calender() {
        //Initializes array 
        String[] events = {"-No event planned-","-No event planned-","-No event planned-","-No event planned-","-No event planned-"};
        //end calender class constructor
}

    //begin createEvent method
    public String[] createEvent (String userEvent, int dayOfWeek){
        //Start switch test
        switch (dayOfWeek){
            case 1: 
                events[0] = ("Monday Appoinment:") + userEvent;
                break; 
            case 2: 
                events[1] = ("Tuesday Appoinment:") + userEvent;
                break; 
            case 3: 
                events[2] = ("WednsdayAppoinment:") + userEvent;
                break;
            case 4: 
                events[3] = ("Thursday Appoinment:") + userEvent;
                break;
            case 5: 
                events[4] = ("Friday Appoinment:") + userEvent;
                break;
            default:
                break;
                //End switch test   
        }
        //returns events array   
        return events;
        //end create event method   
    }
    //end calender class    
}

Answer 1

import java.util.Scanner;

//begin class driver       
public class driver {

/**
 * @paramargs the command line arguments
 */
//begin main method
    public static void main(String[] args) {
    //initiates scanner
        Scanner userInput = new Scanner (System.in);

    //declare variables
    int dayOfWeek;
    String userEvent;

    //creates object for calender class
    calender calenderObject = new calender();
    calender.fillArray();

    //user prompt
    System.out.println("Enter day of week for your event in the following format:");
    System.out.println("Enter 1 for Monday");
    System.out.println("Enter 2 for Tuesday");
    System.out.println("Enter 3 for Wednsday");
    System.out.println("Enter 4 for Thursday");
    System.out.println("Enter 5 for Friday");
    System.out.println("Enter -1 to quit");

    //collect user input
    dayOfWeek = userInput.nextInt(); 

    //user prompt
    System.out.println("Please type in the name of your event");

    //collect user input
    userEvent = userInput.next();

    //begin while loop
    while (dayOfWeek != -1) {
        if ((dayOfWeek>=1) && (dayOfWeek<=5)){
            calenderObject.createEvent(dayOfWeek, userEvent,dayOfWeek);
            for (int i=0;i<calender.length;i++){
                System.out.println(calender.events[i]);
            }
            dayOfWeek = userInput.nextInt();

            if  (dayOfWeek == -1){
                for (int i=0;i<calender.length;i++){
                    System.out.println(calender.events[i]);
                }
                System.exit(0);
            }
            System.out.println("Please type in the name of your event");    
            userEvent = userInput.next();
        } else{
            System.out.println("You have entered an invalid number");
            System.out.println("Press -1 to quit or enter another day");
            System.out.println("Enter 1 for Monday");
            System.out.println("Enter 2 for Tuesday");
            System.out.println("Enter 3 for Wednsday");
            System.out.println("Enter 4 for Thursday");
            System.out.println("Enter 5 for Friday");
            System.out.println("Enter -1 to quit");
            dayOfWeek = userInput.nextInt(); 
        }
    }

    //end main method
}

}

    //begin calender class
public class calender {

    static int length = 5;
    static String[] events = new String[length];

    public static String[] fillArray(){
        for (int i=0; i< length;i++){
            events[i] = "-No event planned-";
        }
        return events;
    }

    //begin createEvent method
public String[] createEvent(int l, String userEvent, int dayOfWeek){
    int t = l;
        if(t%5 == 1 ){
            events[0] = ("Monday Appoinment: ") + userEvent;
        } else if(t%5 == 2 ){
            events[1] = ("Tuesday Appoinment: ") + userEvent;
        } else if(t%5 == 3 ){
            events[2] = ("WednsdayAppoinment: ") + userEvent;
        } else if(t%5 == 4){
            events[3] = ("Thursday Appoinment: ") + userEvent;
        } else if(t%5 == 0 ){
            events[4] = ("Friday Appoinment: ") + userEvent;
        }        
        return events;
    }

//end calender class    
}

Answer 2

You are declaring a local events array inside constructor so default value No event planned is not assigned to your instance variable events it should be

public calender() {
    //Initializes your events array

    events = { "-No event planned-",
               "-No event planned-",
               "-No event planned-",
               "-No event planned-",
               "-No event planned-"};

    //end calender class constructor
}

hope it works

Answer 3

Your main method doesn't know what events is because there's no local variable named events in scope, and no static variable named events on the main class. You need to tell it you're looking for the events object within a specific calendar object, like this:

System.out.println(calendarObject.events[0]);

This assumes your two classes are in the same package, or that both have no package declared (so they are both in the default package). If the two classes are in different packages you would have to either expose the instance member as public or create a public method that accesses it for the other to see it.

The idea of class-based objects is you can use a class to create multiple objects. That might not come across so well in this assignment since you only create one object of your calendar class. For you to reference a member of an object you need to specify which object you're looking for that member within.

Answer 4

Firstly, it said don't hardcode the size, use a constant. So make a constant like so:

private static final int ARRAY_SIZE = 5;

And change your declaration to

String[] events = new String[ARRAY_SIZE];

And when initializing your array, use a for-counter loop to set each slot to be "-No event planned-", rather than just {some number of "-No event planned"s}, as that isn't dynamic, and won't change with your constant size.

Also, in your constructor remove the type declaration

String[] events -> events

By declaring the type, you make a new local variable, rather than modifying the field, and so the slots in the array are all still null, as you never modified them, but rather the fields in this local variable.