Java errors

[CarlMartin10]

Here is the entire code, and the new error. Does the main method need to be in the "Box" class? I need the second class to test the constructors to make sure they all work properly, that is what the book wants me to do.

// Program that ues constructors to assig values (length, width and height) to a box

import javax.swing.JOptionPane;

// Create "Box" class
public class Box
{
	// Declare variables
	private int length;
	private int width;
	private int height;
	
	// Constructors to set length, width, and height
	public Box(int length)
	{
		this.length = length;
		this.width = 0;
		this.height = 0;		
				
		// Display box length
		JOptionPane.showMessageDialog(null, "Line created with length " + length);
		
    }
	public Box(int  length, int width)
	{
		this.length = length;
		this.width = width;
		this.height = 0;
				
		// Display box length and width
		JOptionPane.showMessageDialog(null, "Rectangle created with length " + length + " and width " + width);
		
    }
	 
	 	public Box(int  length, int width, int height)
	{
		this.length = length;
		this.width = width;
		this.height = height;
				
		// Display box length and width
		JOptionPane.showMessageDialog(null, "Box created with length " + length + ", width " + width + ", and height " + height);
		System.exit(0);	
    }	 	 
	}
	
	public class BoxTest
	{
	 // Main method
	 public void main(String[] args)
	{	   
		Box boxOne = new Box(1);
		Box boxTwo = new Box(1,2);
		Box boxThree = new Box(1,2,3);
	}
	}

Error:

Box.java:53: class BoxTest is public, should be declared in a file named BoxTest.java
public class BoxTest
^
1 error