Here is the (simplified) source code. This is mostly a Smalltalk tutorial, so you will need to learn somewhere else how to enter code into the Squeak image. Don't worry, the tools are great and there are quite a few other tutorials out there to help you get started. The first place to go is http://www.squeak.org/.
Object subclass: #Can instanceVariableNames: 'body contents ' classVariableNames: '' poolDictionaries: '' category: 'LunchDemo' comment: This class models a simple can for the LunchDemo tutorial. an is a very simple class that encapsulates two attributes: body and contents. It includes simple accessors, 'getters' and 'setters,' that form the object's public interface. It also includes a demonstration method, 'demoCans.' To test the Can class, select the next line and inspect it: Can new demoCans. body "Returns the current value of the body attribute." ^ body. body: typeofmetal "Sets the value of the body attribute." body_typeofmetal. self contentsChanged contents "Returns the current value of the contents attribute." ^ contents. contents: newContents "Sets the value of the contents attribute." contents_newContents. self contentsChanged demoCans "Demonstrates and tests the class." | mycan othercan | mycan _ Can new. mycan body: 'tin'. mycan contents: 'spam'. othercan _ Can new. othercan body: 'aluminum'. othercan contents: 'cream soda'. (Transcript show: 'mycan:') cr. (Transcript show: ' Body = ', (mycan body)) cr. (Transcript show: ' Contents = ', (mycan contents)) cr. (Transcript show: 'othercan:') cr. (Transcript show: ' Body = ', (othercan body)) cr. (Transcript show: ' Contents', (othercan contents)) cr.