Computer Science II 810:062 Section 01

How is CS I different from CS II? When you teach Java there are a series of decisions that have to be made…

How is CS I different from CS II? When you teach Java there are a series of decisions that have to be made… Applet or Applications Core Java or Textbook package IDE or command line Object Oriented or “structured” Event-driven or “Non-event driven”

When you teach Java there are a series of decisions that have to be made… Applet or Applications Core Java or Textbook package IDE or command line Object Oriented or “structured” Event-driven or “Non-event driven” How is CS I different from CS II?

When you teach Java there are a series of decisions that have to be made… Applet or Applications Core Java or Textbook package IDE or command line Object Oriented or “structured” Event-driven or “Non-event driven”

How is CS I different from CS II? CS I focuses on learning to program in the first place. CS II focuses on learning how to program well using the paradigm of Object Oriented Programming.

So what is OO programming? Object-oriented programming changes the way software developers think about the problem by redefining the problem. Object-oriented programming encourages us to think about the computer as a simulator of the world. Thus, a program is a map of the world we want to imitate.

So what is OO programming? Instead of asking –How can I write a program that is structured like the machine on which it runs? We ask –How can I write a program that is structured like the part of the world it describes?

So what is OO programming?

The anatomy of an OO program The world consists of objects that interact to solve a problem.

So what is OO programming? “In Java, the main thing you do is write class definitions.” (R. Morelli) A class definition encapsulates two (three actually) things: –Data (instance variables) –Actions (constructors and methods).

So what is OO programming? But a class on its own is nearly worthless. The purpose of a class is to serve as a template for creating individual objects, or instances, of the class.

The anatomy of an OO program An object is an instance of a class MemoPad p = new MemoPad(); While a class describes a set of objects that behave similarly, each instance of a class is distinct and has its own state. MemoPad p = new MemoPad(); MemoPad q = new MemoPad();

So what is OO programming? an object-oriented program is a set of objects that collaborate to achieve a goal objects interact by sending each other messages (invoking an object’s method).

Let’s consider a MemoPad example Allows for the storage of a collection of memos that are associated with keys

For example, you can insert an memo:

Identify the objects needed in the MemoPadApp example List the objects and their behaviors

What came first the chicken or the egg? Since objects create other objects dynamically as needed, where does the first object come from?

The anatomy of an OO program The world is a class that contains the main() function. main() is the “big bang” that creates one or more objects. public class MemoPadApp { public static void main( String [] args ) { MemoPad p = new MemoPad(); p.show(); } // end main } // end class MemoPadApp

So what is OO programming? Notice that “main” is a static method. We will discuss what static means in more detail later this semester, but for now you can think of this modifier as saying that main is associated with the class memoPadApp, and not with any instance of the class. “main” is a class method.

So what is OO programming? an object-oriented program is a set of objects that collaborate to achieve a goal objects interact by sending each other messages (invoking an object’s method).

So how do objects collaborate? They send one another messages. In response to a message, an object executes the method associated with the message that it receives, both names and arguments. A big part of designing an object-oriented system is deciding what messages each object should respond to. The set of messages to which an object responds is called its interface.

Designed an interface for the memo database class the memo database class is used to hold the actual memos being stored its interface is the set of messages to which it should respond

Think about: What is the behavior of a memo database? What should it do in order to contribute to the world of objects that implements the behavior of a memo pad?

Interface for the memo database public interface MemoDatabase { } // end interface MemoDatabase

Interface for the memo database public interface MemoDatabase { public String find ( String key ); } // end interface MemoDatabase

Interface for the memo database public interface MemoDatabase { public String find ( String key ); public boolean remove ( String key ); public boolean insert (MemoAssociation m); public boolean containsKey( String key ); } // end interface MemoDatabase

For next class Read chapter 1. Identify any concepts or terms that are new to you so we can discuss them. Re-acquaint yourself with the Java tools available at home or in the lab. Download the MemoPad code from the course Java page, and play with it.