Question

A brief background before so we can communicate on the same wave length. I’ve had about 8-10 university courses on programming from data structure, to one on all languages, to specific ones such as java & c++. I’m a bit rusty because i usually take 2-3 month breaks from coding. This is a personal project that I started thinking of two years back.

Okay down to the details, and a specific question, I’m having problems with my mutator functions. It seems to be that I am trying to access a private variable incorrectly. The question is, am I nesting my classes too much and trying to mutate a base class variable the incorrect way. If so point me in the way of the correct literature, or confirm this is my problem so I can restudy this information. Thanks

package GroceryReceiptProgram;

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

public class Date {

    private int hour, minute, day, month, year;

    Date() {
        try {
            BufferedReader keyboard = new BufferedReader(new InputStreamReader(System.in));
            System.out.println("What's the hour? (Use 1-24 military notation");
            hour = Integer.parseInt(keyboard.readLine());
            System.out.println("what's the minute? ");
            minute = Integer.parseInt(keyboard.readLine());
            System.out.println("What's the day of the month?");
            day = Integer.parseInt(keyboard.readLine());
            System.out.println("Which month of the year is it, use an integer");
            month = Integer.parseInt(keyboard.readLine());
            System.out.println("What year is it?");
            year = Integer.parseInt(keyboard.readLine());
            keyboard.close();
        } catch (IOException e) {
            System.out.println("Yo houston we have a problem");
        }

    }

    public void setHour(int hour) {
        this.hour = hour;
    }

    public void setHour() {
        try {
            BufferedReader keyboard = new BufferedReader(new InputStreamReader(System.in));
            System.out.println("What hour, use military notation?");
            this.hour = Integer.parseInt(keyboard.readLine());
            keyboard.close();
        } catch (NumberFormatException e) {
            System.out.println(e.toString() + ":doesnt seem to be a number");
        } catch (IOException e) {
            System.out.println(e.toString());
        }
    }

    public int getHour() {
        return hour;
    }

    public void setMinute(int minute) {
        this.minute = minute;
    }

    public void setMinute() {
        try (BufferedReader keyboard = new BufferedReader(new InputStreamReader(System.in))) {
            System.out.println("What minute?");
            this.minute = Integer.parseInt(keyboard.readLine());
        } catch (NumberFormatException e) {
            System.out.println(e.toString() + ": doesnt seem to be a number");
        } catch (IOException e) {
            System.out.println(e.toString() + ": minute shall not cooperate");
        } catch (NullPointerException e) {
            System.out.println(e.toString() + ": in the setMinute function of the Date class");
        }
    }

    public int getMinute() {
        return minute;
    }

    public void setDay(int day) {
        this.day = day;
    }

    public void setDay() {
        try {
            BufferedReader keyboard = new BufferedReader(new InputStreamReader(System.in));
            System.out.println("What day 0-6?");
            this.day = Integer.parseInt(keyboard.readLine());
            keyboard.close();
        } catch (NumberFormatException e) {
            System.out.println(e.toString() + ":doesnt seem to be a number");
        } catch (IOException e) {
            System.out.println(e.toString());
        }
    }

    public int getDay() {
        return day;
    }

    public void setMonth(int month) {
        this.month = month;
    }

    public void setMonth() {
        try {
            BufferedReader keyboard = new BufferedReader(new InputStreamReader(System.in));
            System.out.println("What month 0-11?");
            this.month = Integer.parseInt(keyboard.readLine());
            keyboard.close();
        } catch (NumberFormatException e) {
            System.out.println(e.toString() + ":doesnt seem to be a number");
        } catch (IOException e) {
            System.out.println(e.toString());
        }
    }

    public int getMonth() {
        return month;
    }

    public void setYear(int year) {
        this.year = year;
    }

    public void setYear() {
        try {
            BufferedReader keyboard = new BufferedReader(new InputStreamReader(System.in));
            System.out.println("What year?");
            this.year = Integer.parseInt(keyboard.readLine());
            keyboard.close();
        } catch (NumberFormatException e) {
            System.out.println(e.toString() + ":doesnt seem to be a number");
        } catch (IOException e) {
            System.out.println(e.toString());
        }
    }

    public int getYear() {
        return year;
    }

    public void set() {
        setMinute();
        setHour();
        setDay();
        setMonth();
        setYear();
    }

    public Vector<Integer> get() {
        Vector<Integer> holder = new Vector<Integer>(5);
        holder.add(hour);
        holder.add(minute);
        holder.add(month);
        holder.add(day);
        holder.add(year);
        return holder;
    }
};

That is the Date class obviously, next is the other base class Location.

package GroceryReceiptProgram;

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

    public class Location {

        String streetName, state, city, country;
        int zipCode, address;

        Location() {
            try {
                BufferedReader keyboard = new BufferedReader(new InputStreamReader(System.in));
                System.out.println("What is the street name");
                streetName = keyboard.readLine();
                System.out.println("Which state?");
                state = keyboard.readLine();
                System.out.println("Which city?");
                city = keyboard.readLine();
                System.out.println("Which country?");
                country = keyboard.readLine();
                System.out.println("Which zipcode?");//if not u.s. continue around this step
                zipCode = Integer.parseInt(keyboard.readLine());
                System.out.println("What address?");
                address = Integer.parseInt(keyboard.readLine());
            } catch (IOException e) {
                System.out.println(e.toString());
            }
        }

        public void setZipCode(int zipCode) {
            this.zipCode = zipCode;
        }

        public void setZipCode() {
            try {
                BufferedReader keyboard = new BufferedReader(new InputStreamReader(System.in));
                System.out.println("What zipCode?");
                this.zipCode = Integer.parseInt(keyboard.readLine());
                keyboard.close();
            } catch (NumberFormatException e) {
                System.out.println(e.toString() + ":doesnt seem to be a number");
            } catch (IOException e) {
                System.out.println(e.toString());
            }
        }

        public void set() {
            setAddress();
            setCity();
            setCountry();
            setState();
            setStreetName();
            setZipCode();
        }

        public int getZipCode() {
            return zipCode;
        }

        public void setAddress(int address) {
            this.address = address;
        }

        public void setAddress() {
            try {
                BufferedReader keyboard = new BufferedReader(new InputStreamReader(System.in));
                System.out.println("What minute?");
                this.address = Integer.parseInt(keyboard.readLine());
                keyboard.close();
            } catch (NumberFormatException e) {
                System.out.println(e.toString() + ":doesnt seem to be a number");
            } catch (IOException e) {
                System.out.println(e.toString());
            }
        }

        public int getAddress() {
            return address;
        }

        public void setStreetName(String streetName) {
            this.streetName = streetName;
        }

        public void setStreetName() {
            try {
                BufferedReader keyboard = new BufferedReader(new InputStreamReader(System.in));
                System.out.println("What minute?");
                this.streetName = keyboard.readLine();
                keyboard.close();
            } catch (IOException e) {
                System.out.println(e.toString());
            }
        }

        public String getStreetName() {
            return streetName;
        }

        public void setState(String state) {
            this.state = state;
        }

        public void setState() {
            try {
                BufferedReader keyboard = new BufferedReader(new InputStreamReader(System.in));
                System.out.println("What minute?");
                this.state = keyboard.readLine();
                keyboard.close();
            } catch (IOException e) {
                System.out.println(e.toString());
            }
        }

        public String getState() {
            return state;
        }

        public void setCity(String city) {
            this.city = city;
        }

        public void setCity() {
            try {
                BufferedReader keyboard = new BufferedReader(new InputStreamReader(System.in));
                System.out.println("What minute?");
                this.city = keyboard.readLine();
                keyboard.close();
            } catch (IOException e) {
                System.out.println(e.toString());
            }
        }

        public String getCity() {
            return city;
        }

        public void setCountry(String country) {
            this.country = country;
        }

        public void setCountry() {
            try {
                BufferedReader keyboard = new BufferedReader(new InputStreamReader(System.in));
                System.out.println("What minute?");
                this.country = keyboard.readLine();
                keyboard.close();
            } catch (IOException e) {
                System.out.println(e.toString());
            }
        }

        public String getCountry() {
            return country;
        }
    };

their parent(What is the proper name?) class

package GroceryReceiptProgram;

    import java.io.*;

    public class FoodGroup {

        private int price, count;
        private Date purchaseDate, expirationDate;
        private Location location;
        private String name;

        public FoodGroup() {
            try {
                setPrice();
                setCount();
                expirationDate.set();
                purchaseDate.set();
                location.set();
            } catch (NullPointerException e) {
                System.out.println(e.toString() + ": in the constructor of the FoodGroup class");
            }
        }

        public void setPrice(int price) {
            this.price = price;
        }

        public void setPrice() {
            try (BufferedReader keyboard = new BufferedReader(new InputStreamReader(System.in))) {
                System.out.println("What Price?");
                price = Integer.parseInt(keyboard.readLine());

            } catch (NumberFormatException e) {
                System.out.println(e.toString() + ":doesnt seem to be a number");
            } catch (IOException e) {
                System.out.println(e.toString() + ": in the FoodGroup class, setPrice function");
            } catch (NullPointerException e) {
                System.out.println(e.toString() + ": in FoodGroup class. SetPrice()");
            }
        }

        public int getPrice() {
            return price;
        }

        public void setCount(int count) {
            this.count = count;
        }

        public void setCount() {
            try (BufferedReader keyboard = new BufferedReader(new InputStreamReader(System.in))) {
                System.out.println("What count?");
                count = Integer.parseInt(keyboard.readLine());

            } catch (NumberFormatException e) {
                System.out.println(e.toString() + ":doesnt seem to be a number");
            } catch (IOException e) {
                System.out.println(e.toString() + ": in the FoodGroup class, setCount()");
            } catch (NullPointerException e) {
                System.out.println(e.toString() + ": in FoodGroup class, setCount");
            }
        }

        public int getCount() {
            return count;
        }

        public void setName(String name) {
            this.name = name;
        }

        public void setName() {
            try {
                BufferedReader keyboard = new BufferedReader(new InputStreamReader(System.in));
                System.out.println("What minute?");
                this.name = keyboard.readLine();

            } catch (IOException e) {
                System.out.println(e.toString());
            }
        }

        public String getName() {
            return name;
        }

        public void setLocation(Location location) {
            this.location = location;
        }

        public Location getLocation() {
            return location;
        }

        public void setPurchaseDate(Date purchaseDate) {
            this.purchaseDate = purchaseDate;
        }

        public void setPurchaseDate() {
            this.purchaseDate.set();
        }

        public Date getPurchaseDate() {
            return purchaseDate;
        }

        public void setExpirationDate(Date expirationDate) {
            this.expirationDate = expirationDate;
        }

        public void setExpirationDate() {
            this.expirationDate.set();
        }

        public Date getExpirationDate() {
            return expirationDate;
        }
    }

and finally the main class, so I can get access to all of this work.

    package GroceryReceiptProgram;


    public class NewMain {


        public static void main(String[] args) {
            FoodGroup test = new FoodGroup();
        }
    }

If anyone is further interested, here is a link the UML for this.

https://www.dropbox.com/s/1weigjnxih70tbv/GRP.dia

Answer 1

There is a problem in your FoodGroup constructor, you haven’t initialized some of the instance variables, so their taking the null default valu, giving you problems:

public FoodGroup() {
    //...
    //null pointer exception here!
    expirationDate.set();
    //null pointer exception here!
    purchaseDate.set();
    //null pointer exception here!
    location.set();
    //...
}

This problem can be solved by creating those variables before using them:

public FoodGroup() {
    //...
    expirationDate = new Date();
    //not null pointer exception!
    expirationDate.set();
    //similar to the other cases
    //...
}

Some advices for this and future projects:

• Don’t create classes that has a similar name that classes in the Java API. For example, your Date class can easily be misunderstood with java.util.Date.
• Don’t use the Vector class, instead use List<YourClass> list = new ArrayList<YourClass>(). More info here: What are the differences between ArrayList and Vector? and Why is Java Vector class considered obsolete or deprecated?(this one is from Jon Skeet).
• Try to use public constructors for your classes. In your case, your program will compile and run just because all your classes are in the same package, but if they were in different packages, there will be a problem because almost all the constructors has the default visibility and can only be seen by classes of the same package. Take note about it: Controlling Access to Members of a Class
• FoodGroup is not a parent class, it is a “has-a” relationship between 1) FoodGroup and Date, 2) FoodGroup and Location. It could be seen as a controller who controls the behavior and live of both classes instances.
• When you post code here or other sites, please post a SSCCE instead of your whole code. In that way, it will be easier for anyone to help you.