How to use a class in Java?

[Arc]

Hey guys I have created a class which compiles fine, but I am having trouble trying to use it in a program. I am not clear on how to instantiate the class in a program can you give me an example of how to do this?


Thanks!

Here are my class and program so far.


The Class....................................................

public class Rectangle{

    private double length = 1;
    private double width = 1;


        public double getLength(){

            return length;

        }//end getLength

        public void setLength(double l){

            if(l > 0.0 && l < 20.0){
                length = l;
            }/// end if

        }// end setLength

        public double getWidth(){

            return width;

        }//end getWidth

        public void setWidth(double w){

            if(w > 0.0 && w < 20.0){
                width = w;
            }// end if

        }//end setWidth

        public double perimeter(){

            double thePerimeter = 0;

            thePerimeter = length * 2 + width * 2;

            return thePerimeter;

        }//end perimeter

        public double area(){

                    double theArea = 0;

                    theArea = length * width;

                    return theArea;

        }//end perimeter



}//end class Rectangle 

The program to use it...........................

import javax.swing.JOptionPane;


public class RectangleTest{
    private Rectangle testIt;

    public static void main( String Args[] ){

        testIt = new Rectangle();

        testIt.setLength(5.0);
        testIt.setWidth(6.0);

       JOptionPane.showMessageDialog(null, "The rectangle's width perimeter is: "
       + testIt.perimeter + "\nThe rectangle's area is: "
       + testIt.area, "Results", JOptionPane.PLAIN_MESSAGE);


    }//end main



}//end class Rectangle 

These are the errors I get

C:\...\RectangleTest.java:12: non-static variable testIt cannot be referenced from a static context
testIt = new Rectangle();
^
C:\...\RectangleTest.java:14: non-static variable testIt cannot be referenced from a static context
testIt.setLength(5.0);
^
C:\...\RectangleTest.java:15: non-static variable testIt cannot be referenced from a static context
testIt.setWidth(6.0);
^
C:\...\RectangleTest.java:18: non-static variable testIt cannot be referenced from a static context
+ testIt.perimeter + "\nThe rectangle's area is: "
^
C:\...\RectangleTest.java:18: cannot find symbol
symbol : variable perimeter
location: class Rectangle
+ testIt.perimeter + "\nThe rectangle's area is: "
^
C:\...\RectangleTest.java:19: non-static variable testIt cannot be referenced from a static context
+ testIt.area, "Results", JOptionPane.PLAIN_MESSAGE);
^
C:\...\RectangleTest.java:19: cannot find symbol
symbol : variable area
location: class Rectangle
+ testIt.area, "Results", JOptionPane.PLAIN_MESSAGE);

I'm not sure what the errors mean or what I am doing wrong...