import java.io.Serializable;
public class Rectangle implements Serializable
{
  private double length, width;
  public Rectangle(double l, double w)
  {
    length = l; width = w;
  }
  public void setDimension(double l, double w)
  {
    length = l; width = w;
  }
  public double getArea()
  {
    return length * width;
  }
  public String toString()
  {
    return length + " x " + width + " = " + getArea();
  }
}

============================================
import java.io.*;
import java.util.*;
public class Main
{
  public static void main(String[] args)
  {

  }
  public static void readList()
  {
    try(ObjectInputStream is =
          new ObjectInputStream(
            new FileInputStream("list.dat")))
    {
      Object data = is.readObject();
      ArrayList<Rectangle> rList =
        (ArrayList<Rectangle>)data;
      Iterator<Rectangle> itor = rList.iterator();
      while (itor.hasNext())
        System.out.println(itor.next());
    }
    catch(FileNotFoundException e)
    {
      System.out.println(e);
    }
    catch(IOException | ClassNotFoundException e)
    {
      System.out.println(e);
    }
  }
  public static void saveList()
  {
    try(ObjectOutputStream os =
          new ObjectOutputStream(
            new FileOutputStream("list.dat")))
    {
      ArrayList<Rectangle> rList = new ArrayList();
      rList.add(new Rectangle(10, 1));
      rList.add(new Rectangle(20, 2));
      rList.add(new Rectangle(30, 3));
      os.writeObject(rList);
    }
    catch(FileNotFoundException e)
    {
      System.out.println(e);
    }
    catch(IOException e)
    {
      System.out.println(e);
    }

  }
  public static void readRectangle()
  {
    try(ObjectInputStream is =
          new ObjectInputStream(
            new FileInputStream("object.dat")))
    {
      Rectangle r = (Rectangle)is.readObject();
      System.out.println(r);

      System.out.println(is.readObject());
      System.out.println(is.readObject());
      // Testing
      r.setDimension(100, 20);
      System.out.println(r);

      System.out.println("End of readRectangle");
    }
    catch(FileNotFoundException e)
    {
      System.out.println(e);
    }
    catch(IOException | ClassNotFoundException e)
    {
      System.out.println(e);
    }
  }

  public static void saveRectangle()
  {
    try(ObjectOutputStream os =
          new ObjectOutputStream(
            new FileOutputStream("object.dat")))
    {
      os.writeObject(new Rectangle(10, 2));
      os.writeObject(new Rectangle(20, 4));
      os.writeObject(new Rectangle(30, 3));
      System.out.println("End of saveRectangle");
    }
    catch(FileNotFoundException e)
    {
      System.out.println(e);
    }
    catch(IOException e)
    {
      System.out.println(e);
    }
  }
}