How to call a master constructor from a minor constructor?

I'm writing a program where i want to call the master constructor from a minor constructor. I have wrote

Code:

---

public Track(String artist, String title, String album, int year,
                        Genre genre) {
                // check parameters and assign data fields
                assignValues(artist, title, album, year, genre);
        }
public Track(String artist, String title, String album, Genre genre) {
                // TODO: put specified parameters alongside with default values
                // for the unspecified ones into the master constructor
                // (or into a higher tier minor constructor)
                this.artist = DEFAULT_ARTIST;
                this.title = DEFAULT_TITLE;
                this.album = DEFAULT_TITLE;
                this.genre = DEFAULT_GENRE;
        }

---

but i'm not sure if i've done it right...

Recommended reading: Using the this Keyword (The Java™ Tutorials > Learning the Java Language > Classes and Objects)

thnx for the link!!! I tried to understand that but i guess i'm missing sth here.
i wrote a test method for the program but still i don't get the result i want.
Can somebody tell me what i do wrong? I get null values in the end :S:S

Code:

---

import java.util.Calendar;
import java.lang.Object;

public class Song {

        /**
        * enumeration for different music genres (just a few examples implemented
        * here)
        */
        public enum Genre {
                UNDEFINED, POP, ROCK, ALTERNATIVE, ELECTRONIC, INDUSTRIAL
        }

        /**
        * global constants
        */
        // number of data fields (artist, title, album, year, genre)
        private static final int NUMBER_OF_FIELDS = 5;
        // max. length of artist-, title- and album-strings
        private static final int MAX_STRING_LENGTH = 30;
        // abbreviation character for strings exceeding max. length
        private static final char ABBREVIATION_CHAR = '.';

        /**
        * constant default values for all meta data fields
        */
        private static final String DEFAULT_ARTIST = "";
        private static final String DEFAULT_TITLE = "";
        private static final String DEFAULT_ALBUM = "";
        private static final int DEFAULT_YEAR = 0;
        private static final Genre DEFAULT_GENRE = Genre.UNDEFINED;
       
        /**
        * data fields holding meta information on music tracks
        */
        private String artist;
        private String title;
        private String album;
        private int year;
        private Genre genre;

        /**
        * master constructor: takes all parameters, checks them for validity and
        * assigns them to the data fields
        */
        public Song(String artist, String title, String album, int year,
                        Genre genre) {
                // check parameters and assign data fields
                assignValues(artist, title, album, year, genre);
        }

        /**
        * minor constructor: calls master constructor
        */
        public Song(String artist, String title, String album, int year) {
                // putting the specified parameters alongside with default value
                // of genre into the master constructor
                assignValues(artist, title, album, year, DEFAULT_GENRE);
        }

        /**
        * minor constructor: calls master constructor
        */
        public Song(String artist, String title, String album, Genre genre) {
                //put specified parameters alongside with default values
                // for the unspecified ones into the master constructor
                // (or into a higher tier minor constructor)
                assignValues(artist, title, album, DEFAULT_YEAR, genre);
        }

        /**
        * minor constructor: calls master constructor
        */
        public Song(String artist, String title, int year, Genre genre) {
                //put specified parameters alongside with default values
                // for the unspecified ones into the master constructor
                // (or into a higher tier minor constructor)
                assignValues(artist, title, DEFAULT_ALBUM, year, genre);
        }

        /**
        * minor constructor: calls master constructor
        */
        public Song(String artist, String title, String album) {
                //put specified parameters alongside with default values
                // for the unspecified ones into the master constructor
                // (or into a higher tier minor constructor)
                assignValues(artist, title, album, DEFAULT_YEAR, DEFAULT_GENRE);
        }

        /**
        * minor constructor: calls master constructor
        */
        public Song(String artist, String title, int year) {
                //put specified parameters alongside with default values
                // for the unspecified ones into the master constructor
                // (or into a higher tier minor constructor)
                assignValues(artist, title, DEFAULT_ALBUM, year, DEFAULT_GENRE);
        }

        /**
        * minor constructor: calls master constructor
        */
        public Song(String artist, String title, Genre genre) {
                //put specified parameters alongside with default values
                // for the unspecified ones into the master constructor
                // (or into a higher tier minor constructor)
                assignValues(artist, title, DEFAULT_ALBUM, DEFAULT_YEAR, genre);
        }

        /**
        * minor constructor: calls master constructor
        */
        public Song(String artist, String title) {
                // put specified parameters alongside with default values
                // for the unspecified ones into the master constructor
                // (or into a higher tier minor constructor)
                assignValues(artist, title, DEFAULT_ALBUM, DEFAULT_YEAR, DEFAULT_GENRE);
               
        }

       
        /**
        * validity check: checks string length and year number for validity and
        * applies changes if necessary before assigning them to the data fields
        */
        private void assignValues(String artist, String title, String album,
                        int year, Genre genre) {
                // check String parameters and shorten the
                // if necessary (trimText-method)
                if (artist.length()>10){
                        artist = transfuse(artist, ABBREVIATION_CHAR , 10);
                }
                if (title.length()>10){
                        title = transfuse(title, ABBREVIATION_CHAR , 10);
                }
                if (album.length()>10){
                        album = transfuse(album, ABBREVIATION_CHAR , 10);
                }


                //check year not to be smaller than DEFAULT_YEAR or
                // larger than current year
                Calendar cal = Calendar.getInstance();
                int currentYear = cal.get(java.util.Calendar.YEAR);
                if(year<DEFAULT_YEAR && year>currentYear){
                        System.out.println("Year not valid");
                }

                //assign genre parameter without any validity check
                genre = DEFAULT_GENRE;
        }
       
       
       
        /**
        * overloads original method from java.lang.object
        *
        * @return single string representation of all data fields
        */
        public String toString() {
                return artist + " | " + title + " | " + album + " | " + year + " | "
                                + genre;
        }

        /**
        * trims a string to a specified length and appends an abbreviation character
        */
        private static String transfuse(String text, char c, int length) {
                // implement functionality
                // transfuse("long text parameter", '.', 10);
                // --> "long text."
                if (text != null && text.length() > length && c == '.')
                            text = text.substring(0, length-1) + '.';
                          return text;
        }
       
        public static void main(String args[]){
                Song p = new Song("Queens","We will rock you");
                System.out.println(p);
                }

}

---

I have no idea what a master constructor or a minor constructor is.

You can have a constructor that does nothing.
You can have a constructor that initialises instance variables.
You can have a constructor that calls a method.
You can have a constructor that calls another constructor in the same class.
You can have a constructor that calls a constructor in the parent class. (which is does by default)

I have no idea what your problem is. If you are getting error messages then copy and paste the full message and indicate on which line they occur.

I just had a look at your assignValues method. Your problem is that the parameters and instance variables have the same names.

Quote:

---

Originally Posted by Junky

I just had a look at your assignValues method. Your problem is that the parameters and instance variables have the same names.

---

b.m, and the solution to that is in the link I gave you!