compile error

[jamie keene]

I think i have the codes right, and the main method was provided, yet i am getting errors in both methods

public class LandTract
{
	//Declare variables
	private double length;
	private double width;
	private double area;
	
	//Constructor
	public LandTract(double l, double w)
	{
		length = l;
		width = w;
	}
	
	//Return area
	public double getArea()
	{
		area = length * width;
		return area;
	}
	
	//to string method
	public String toString()
	{
		String str = "length is " + length +
				", width is " + width + ", area is " +
				area;
		return str;
	}
}

this compiles with no error

this is the provided main method, which i can not compile

 import java.util.Scanner;

   public class LandTractDemo
   {
      public static void main(String[] args)
      {
      // local variables
         double length;          
         double width;       
         
      // Create a Scanner object for keyboard input
         Scanner keyboard = new Scanner(System.in);
     
      // Get the dimensions of tract 1
         System.out.print("Enter the length and width of Tract 1: ");
         length = keyboard.nextDouble();
         width = keyboard.nextDouble();
     
      // Create a LandTract object for tract 1
			LandTract tract1 = new LandTract(length, width);
			
		// Get the dimensions of tract 2
			System.out.print("Enter the length and width of Tract 2: ");
         length = keyboard.nextDouble();
         width = keyboard.nextDouble();
     
      // Create a LandTract object for tract 2
         LandTract tract2 = new LandTract(length, width);
     
      // Display the land tract data
         System.out.println("\nTRACT 1: " + tract1);
         System.out.println("TRACT 2: " + tract2 + "\n");
     
      // Determine whether the two tracts are equal
         if (tract1.equals(tract2))
            System.out.println("The tracts are the same size");
         else
            System.out.println("The tracts are NOT the same size");
      }
   }

error is :

----jGRASP exec: javac -g LandTractDemo.java
LandTractDemo.java:20: cannot find symbol
symbol : class LandTract
location: class LandTractDemo
LandTract tract1 = new LandTract(length, width);
^
LandTractDemo.java:20: cannot find symbol
symbol : class LandTract
location: class LandTractDemo
LandTract tract1 = new LandTract(length, width);
^
LandTractDemo.java:28: cannot find symbol
symbol : class LandTract
location: class LandTractDemo
LandTract tract2 = new LandTract(length, width);
^
LandTractDemo.java:28: cannot find symbol
symbol : class LandTract
location: class LandTractDemo
LandTract tract2 = new LandTract(length, width);
^
4 errors

----jGRASP wedge: exit code for process is 1.

[Mohamed Sanaulla]

Have you defined the CLASSPATH variable? If yes, what is its value?

[Suresh Sajja]

compiler cant find class LandTract. we have to add user classes to the class path.

try using -cp option with javac
to include current directory to class path, use "."

[jamie keene]

so i got it to work, i had miss named something in one of the files, but now it is returning an area of 0.0

public class LandTract
{
	//Declare variables
	private double length;
	private double width;
	private double area;
	
	//Constructor
	public LandTract(double l, double w)
	{
		length = l;
		width = w;
	}
	

	
	//Return area
	public double getArea()
	{
		area = (length * width);
		return area;
	}
	
	//to string method
	public String toString()
	{
		String str = "length is " + length +
				", width is " + width + ", area is " +
				area;
		return str;
	}
}

 import java.util.Scanner;

   public class LandTractDemo
   {
      public static void main(String[] args)
      {
      // local variables
         double length;          
         double width;       
         
      // Create a Scanner object for keyboard input
         Scanner keyboard = new Scanner(System.in);
     
      // Get the dimensions of tract 1
         System.out.print("Enter the length and width of Tract 1: ");
         length = keyboard.nextDouble();
         width = keyboard.nextDouble();
     
      // Create a LandTract object for tract 1
			LandTract tract1 = new LandTract(length, width);
			
		// Get the dimensions of tract 2
			System.out.print("Enter the length and width of Tract 2: ");
         length = keyboard.nextDouble();
         width = keyboard.nextDouble();
     
      // Create a LandTract object for tract 2
         LandTract tract2 = new LandTract(length, width);
     
      // Display the land tract data
         System.out.println("\nTRACT 1: " + tract1);
         System.out.println("TRACT 2: " + tract2 + "\n");
     
      // Determine whether the two tracts are equal
         if (tract1.equals(tract2))
            System.out.println("The tracts are the same size");
         else
            System.out.println("The tracts are NOT the same size");
      }
   }

return looks like this

----jGRASP exec: java LandTractDemo

Enter the length and width of Tract 1: 10 20
Enter the length and width of Tract 2: 15 25

TRACT 1: length is 10.0, width is 20.0, area is 0.0
TRACT 2: length is 15.0, width is 25.0, area is 0.0

The tracts are NOT the same size

----jGRASP: operation complete.

[Matthew Brown]

The problem with the way you've written it at the moment is that the area member variable of LandTract doesn't get initialised until you call getArea(), and you're not calling that.

There are a couple of simple fixes I could suggest:

1. Set area = length*width in the constructor, and in getArea() just return the value of area without doing the calculation.

or

2. Get rid of the area variable. The body of getArea() becomes just return length*width. In toString, call getArea() insetad of using area.

I'd usually go for 2, as that way you don't have a seperate variable that needs to be kept in sync with length and width.

[jamie keene]

thank you, that helped, but now i am stuck on doing a margin of error
this is what i have

 import java.util.Scanner;

   public class LandTractDemo
   {
      public static void main(String[] args)
      {
      // local variables
         double length;          
         double width;
			final double MARGIN_OF_ERROR = 0.01;
			
      // Create a Scanner object for keyboard input
         Scanner keyboard = new Scanner(System.in);
     
      // Get the dimensions of tract 1
         System.out.print("Enter the length and width of Tract 1: ");
         length = keyboard.nextDouble();
         width = keyboard.nextDouble();
     
      // Create a LandTract object for tract 1
			LandTract tract1 = new LandTract(length, width);
			
		// Get the dimensions of tract 2
			System.out.print("Enter the length and width of Tract 2: ");
         length = keyboard.nextDouble();
         width = keyboard.nextDouble();
     
      // Create a LandTract object for tract 2
         LandTract tract2 = new LandTract(length, width);
     
      // Display the land tract data
         System.out.println("\nTRACT 1: " + tract1);
         System.out.println("TRACT 2: " + tract2 + "\n");
     
      // Determine whether the two tracts are equal
		double difference = (tract1 - tract2);
		if (Math.abs(difference) <= MARGIN_OF_ERROR)
		{
		System.out.println("The tracts are the same size");
		}
		else
		{
		System.out.println("The tracts are NOT the same size");
		}
      }
   }

but i know that i cant do (tract1 - tract2) but i dont think i can do margin of error with tract1.compareTo(tract2)

[Matthew Brown]

Line 36 should be tract1.getArea() - tract2.getArea(), shouldn't it? Otherwise it looks about right.

[jamie keene]

thanks!