Question

I have a program in Java with several classes, these being:

i) Shape
ii) Square
iii) Rectangle
iv) Circle
v) Triangle
vi) Drawing Canvas
vii) Application

Square, Rectangle, Circle and Triangle all inherit from class Shape

Now, in the Drawing Canvas class, I have two methods, one for writing objects of type Shape to a file and one for reading objects from the file.

This is the code:

The method which saves to the file works perfectly. However, I am having a problem reading the objects from the file and appending them to the Shapes ArrayList.

As it is, the application is given me the error that java.lang.String cannot be cast to shapes_assignment.Shape.

How can I read the text stored in the text file and use it to recreate the objects once more? Thanks 🙂

Answer 1

You need to write a reader that will take the input string, and make a shape out of it. Here is a simple example to show you how this can work, using the Java Date class. Not having your Shape constructors, I can’t write your Shape for you.

Date today=new Date();
long var_to_write=today.getTime();

//Save this in to a file, then read it out as long var_in_file

Date previousTime=new Date(var_in_file);