Java Classes & Object Oriented Programming, Schemes and Mind Maps of Object Oriented Programming

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Java Classes

Object Oriented Programming

Introduction

Object Oriented Programming

• One of the first applications of modern computing was modeling and simulation.
• Scientists soon realized that functions alone were insufficient to model systems intuitively
• If we are going to model a planet we would like to actually create a virtual planet, define how it behaves in our simulated universe, and then just observe it.

Object Oriented Programming

• Even engineers are social animals - we evolved to think about the world in terms of agents and objects (not recursion).
• In many situations we solve large problems by delegation. That is we have workers who specialize in solving a particular problem.
• Those specialists have specific skills that they can apply to a specific class of problems.

Object Oriented Programming

• We can pattern software after a group of specialists at a company working on a problem.
• For example, there are two objects we have used – System.out and System.in.
• System.in is the name of an object who knows all about reading data from the keyboard and putting it into a variable.
• It is easier to ask System.out to do the work than write a program to do it ourselves.

Object Oriented Programming

• When we mail a letter all we have to worry about is following the correct protocol to ensure our letter gets to the right place.
• We have to know where to go, how to pay, the format expected for the destination address and return address, etc.
• In software this protocol is called the interface.
• All objects have to have an interface that clearly defines how we can interact with the object.

Object Oriented Programming

• Almost any problem can be broken up

into objects.

• Objects are defined by three things:

– Their state – this is the information

they contain.

– Their behavior or capabilities – these

are the functions they have access to.

– Their interface – the rules describing

how they interact with other objects in

the system.

Reasons for OOP

Abstraction Encapsulation Information hiding Inheritance Software Engineering Issues

Class: Object Types

• Java uses classes and structures to

define objects

• A Java class is an object type.

• When you create the definition of a

class you are defining the attributes and

behavior of a new type.

• Attributes are data members.
• Behavior is defined by methods.

Information Hiding

• The interface to a class is the list of public data members and methods.
• The interface defines the behavior of the class to the outside world (to other classes and functions that may access variables of your class type).
• The implementation (the code that makes the class work) doesn't matter outside the class.

Information Hiding (cont.)

• This is good because it allows us to change the underlying code without forcing everyone who uses our objects to change their code.
• You can change the implementation and nobody cares! (as long as the interface is the same).

Special Member Functions

• Constructors: called when a new object

is created (instantiated).

• can be many constructors, each can take different arguments
• Garbage Collection. This is why Java is

so popular.

Anatomy of a Class

public class Dog { Dog( String dog_name ){ name = dog_name; } public void bark(){ System.out.println(“woof”); } public string getName() { return name } private String name; }

Put all this in

Dog.java

Accessing Data Members

• Data members are available within each method (as if they were local variables).
• Public data members can be accessed by other functions using the member access operator ".".

Accessing class methods

• Within other class methods, a method can be called just like a function.
• Outside the class, public methods can be called only when referencing an object of the class.