How to call a master constructor from a minor constructor?

[b.m]

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

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...

[KevinWorkman]

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

[b.m]

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

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);
		}

}

[Junky]

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.

[Junky]

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

[KevinWorkman]

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!