[mykohlx43]

I have a homework assignment where I need to pass variables to an object and then sort them. One of them is an array and my teacher never really explained how to pass it to the constructor and then reassign them globally. Can anyone help!? I am not asking for people to solve the homework assignment, just to help me pass the array.


Main

// The "CDCOLLECT" class.
import cs1.Keyboard;
public class CDCOLLECT
{
	public static void main (String[] args)
	{
		System.out.println ("How many Cd's");
		int choice = Keyboard.readInt ();
		CD[] c = new CD [choice];

		int index = 0, cdtracknum;
		String cdname, cdartist;
		boolean answer = false;

		while (answer == false)
		{
			System.out.println ("CD # " + (index + 1));
			System.out.print ("Album's Name?: ");
			cdname = Keyboard.readString ();
			System.out.print ("Artist's Name?: ");
			cdartist = Keyboard.readString ();
			System.out.print ("# of Tracks?: ");
			cdtracknum = Keyboard.readInt ();

			String[] trackname = new String [cdtracknum];
			for (int x = 0; x < cdtracknum; x++)
			{
				System.out.print ("(" + (x + 1) + ")" + "Name of the Tracks?: ");
				trackname [x] = Keyboard.readString ();
			}

			CD cd = new CD (cdname, cdartist, cdtracknum, trackname);
			c [index] = cd;
			if ((index + 1) == choice)
				break;
			index++;

			System.out.println (cd); // this is where i am testing to see if it printed anything
											   // and it doens't print it
		}
	} 
} 

Object File

public class CD implements Comparable
{
	String name, artist;
	String[] trackname = new String [30];
	int tracknum;
	public CD (String cdname, String cdartist, int cdtracknum, String[] trackname1)
	{
		name = cdname;
		artist = cdartist;
		tracknum = cdtracknum;

		// is this correct???

		for (int x = 0; x < trackname1.length; x++)
		{
			trackname [x] = trackname1 [x];
		}
	}

	public int compareTo (Object o)
	{
		return -1;
	}

	public String toString ()
	{
		return trackname [0]; // I am trying to print it out to see if it worked
	}
}

[TriggaMike]

It looks like you are accepting the array as an argument in the constructor. Can you be more specific? Is something not working in your program, if so what?

[mostyfriedman]

yea, you got the array part tight

[mykohlx43]

well when i run the program everything works except when i try to print out the variable. It gives me nothing when i print it out, so i feel like something is getting lost when i am reassigning it. I know i'm a beginner, but what does accepting it as an argument mean?

[mostyfriedman]

well its supposed to print the element, try using the "this" keyword

 for (int x = 0; x < trackname1.length; x++)
		{
		   this.trackname [x] = trackname1 [x];
		}

[mykohlx43]

i still can't print out the array after reassigning it. i think i'm just gonna pass it directly to the method. w/o globally declaring it

[mostyfriedman]

my apologies but its really late over here now, and am really sleepy..cant think at all..i think other members should be around now like pbl

[TriggaMike]

Ok ok, if you're a beginner I'll give you a few pointers that will make your life easier:

this is your general method definition

[public|private|protected|*default*none of the other words*] [static|*default*without static*] [return type]  [method name] ([argument type] [argument name],...,as many arguments as you want, or none if you don't want any)

Public: The Method is accessible to any other class that has access to the class the method is inside of

Private: The method is only accessible to the class itself.

Protected: The method is accessible to the class, or other classes inside of the same package. You will not use this keyword until later on.

Default: More Strict than Protected, Less Strict than private. I don't recommend using default.



Static: This will be complicated to understand right now, but essentially you should only have a static main method and all other methods should not be static. You will not need to use this keyword for a while other than your main method.




Return Type: This can be anything, from primitive data types (ie. int, double) or objects (String, CD, any other objects you create). CONSTRUCTORS CANNOT HAVE A RETURN STATEMENT. THIS IS DUE TO THE FACT THEY AUTOMATICALLY RETURN A REFERENCE NOT A USABLE VALUE.


Arguments: every method can have 0 or more arguments. You must define both the type of argument, and the name of the argument. This is because it acts like a declaration of a new variable, except it is in the method header.

I hope that helps!

EDIT: When passing Array's and Objects, remember they are passed by REFERENCE not by VALUE. This means that you can edit things inside of them and it will carry back to your main method. This is because an address to a memory location is passed, not a new object or array.

This post has been edited by TriggaMike: 19 January 2009 - 08:26 PM

[mykohlx43]

That did help!! thanks!!

[pbl]

Yes this is correct

	  for (int x = 0; x < trackname1.length; x++)
		{
			trackname [x] = trackname1 [x];
		}

but you are hardcoding the array length to 30
better to

	  trackname = new String[trackname1.length];
	  for (int x = 0; x < trackname1.length; x++)
		{
			trackname [x] = trackname1 [x];
		}