Creating an ArrayList as an attribute

[StudentdotJava]

Hello All,

Maybe it's time I started utilizing forums to help with my programs. I was assigned to create a program which connects to a database, access two tables, take information from the tables and store them as attributes of 2 objects. The only part that is hard for me is adding an ArrayList as an attribute. I am accessing a loan table and a payment table. Everything from the loan table is taken and assigned to the loan object and the payment table to payment object. The thing is every "loan" has payments. He wants us to add an ArrayList called "ArrayList<Payment>" to the loan class as an attribute of the loan object. I am having trouble creating an instance of this in my loan class... can anyone help? This assignment was already graded I just want to know how to do this for future reference (probably on my final exam as well). Thank you.

he's the loan class

import java.util.ArrayList;

public class Loan {
	
	private String loanID; //id no
	private String startDate; //date
	private double annualRate; //loan annual rate
	private double loanAmt; //loan amount due
	private int noYears; //years on loan
	private ArrayList<Payment> payments; //is this correct?
	
	public Loan (String l, String s, double ar, double la, int ny, ArrayList<Payment> p)
	{ loanID = l;
		startDate = s;
		annualRate = ar;
		loanAmt = la;
		noYears = ny;
		ArrayList<Payment> payments = new ArrayList<Payment>(); //this doesn't work
		
		
		/*public Loan ()
		{ this.loanID= loanID;
			this.startDate = startDate;
			this.annualRate= annualRate;
			this.loanAmt = loanAmt;
			this.noYears = noYears;
			ArrayList<Payment> = ArrayList<Payment>();
		//ArrayList <Payment> payments = new ArrayList <Payment>();
		*/
	}//end loan constructor
	
	
	public void setloanID (String l)
	{ 
	loanID = l;
		
	}//end setloanID
	
	public String getloanID ()
	{
		return loanID;
	}//end getloanID
	
	
	public void setstartDate (String s)
	{ 
	startDate = s;
		
	}//end setstartDate
	
	public String getstartDate ()
	{
		return startDate;
	}//end getstartDate
	
	public void setannualRate (double ar)
	{
		annualRate = ar;
	}
	public double getannualRate (double ar)
	{
		
		return annualRate;
	}//end getstartDate
	public void setloanAmt (double la)
{
	loanAmt = la;
}
	public double getloanAmt (double la)
	{
		
		return loanAmt;
	}//end getstartDate
	public void setnoYears (int ny)
	{
		noYears = ny;
	}
	public int getnoYears (int ny)
	{
		
		return noYears;
	}//end getstartDate
	public ArrayList <Payment> getPayments ()
	{
		return payments;
	}//end getPayments
	
}//end loan

[Londbrok]

In your constructor you are creating a new instance of ArrayList that survives only as long as the method is alive. Instead, you have the ArrayList in the parameters, and the instance variable... simply do this:

this.payments=p;

Or you could check if parameter p is null, in which case declare payments as a new ArrayList

this.payments=new ArrayList<Payment>()

That way you avoid having a possible null list.

For some odd reason, you are tumbling on and on from one declaration of an ArrayList to another. Regardless that the variable names equal, they are not the same object, when declared anew (as in ArrayList<Payment> payments=new ArrayList<Payment>(), does not reference your instance variable where as payments=new ArrayList<Payment>() does). There is no namespace collision, because they are not declared within the same brackets. Also, there is a declaration with no variable name what so ever. You can experiment this, by eg. changing the name of the parameter ArrayList also to payments.

Much adviced that you consult the class material, and/or Sun Java tutorials on how variable life span goes.