Chapter 1 Object Orientation: Objects and Classes

What is Programming? Phases of Programming 1.Design 2.Implementation 3.Testing 4.Repeating

Polya’s Four Step Process Four steps to any problem solving activity 1.Understand the problem 2.Devise a solution 3.Test the solution 4.Rework the solution

Solving Computer Problems Need a tool to solve the problem Use a computer language to do this Different levels of languages * 1.Machine Language 2.Assembly Language 3.High Level Language * Some are talking about 4 th Level Languages

Algorithms What is an algorithm? A finite set of steps that specify a sequence of operations to be carried out in order to solve a specific problem.

Properties of Algorithms 1. Finiteness 2. Absence of Ambiguity 3. Definition of Sequence 4. Feasibility 5. Input 6. Output

What is a Computer? Made up of many independent parts all working together –Memory Unit –Arithmetic/Logic Unit (ALU) –Control Unit –Input Devices –Output Devices –Auxiliary Storage Devices Central Processing Unit (CPU)

Memory Unit Can be thought of to look like a giant grid Each square in the grid is a memory location We can access each location in the grid, if we choose to

Objects and Classes When you create a program using an object-oriented language, you are: –Creating a model of the problem –The model is built up from objects in the problem domain –Those objects must be represented in your program

Object vs. Class The difference between an object and a class is subtle. We will examine a student class. If we wanted to identify one particular student, we would need to ask some questions –What color is his hair? –How tall is he? –What is his QCA?

Object vs. Class In order to answer these questions we need to know what student we are talking about. –This particular student object is an instance of the Student class. In this example, the Student is a class and the instance of the Student is a student object.

Object vs. Class A class is a generic example; a blue print if you will. An object is one particular instance of a class. From one set of blue prints we can make multiple instances. All the instances will be unique but based on the same set of blue prints

Convention Names of Classes start with a Capital Letters. Names of objects start with lower case letters. This case convention is fairly well followed throughout the Java programming community.

BlueJ Example Let’s take a look at an example in BlueJ. All the examples in the notes assume that you have BlueJ installed in C:\BlueJ The Shape Example The Shape Example

Calling Methods When we right clicked on a object on the workbench in BlueJ, we got a popup menu with a bunch of function names listed. In Java, these functions are called methods When we chose one of these methods for the object to perform, we called or invoked the method When the method requires information from the programmer, the method is said to have a parameter

Method Signatures A method signature provides information about the method. –It tells us the name of the method –Whether or not the method requires a parameter –What type of information is returned from the method

Data Types The values a parameter can take Examples –int – whole numbers –String – a section of text Pitfall – forgetting the double quotes around a string. You’ll get a message like “Error: undefined variable”

Java Data Types Java supports two kinds of data types Built-in data types Object data types Built-in data types are types like integers, characters, etc. Object data types are like Strings, Arrays, etc.

Built-in Types Java has a limited amount of built-in types. We will be most concerned with int- For integer numbers double- For floating point numbers boolean- For true/false values char – For character data

Object Types There are many objects types. Some are provided for us The others we will create ourselves. There are some object types we can use with no extra work String – For representing strings of characters System – For some basic output

State All of the attributes that define an object is referred to as the object’s state Java refers to the individual attributes as fields

Multiple Instances Object-oriented programming (OOP) allows for creating more than one object from the same class. The internal state of the object allows the computer to tell the different objects apart.

What is an object? All objects of the same class have the same fields (and methods). The values stored in those fields can be different. Simply being an object of a given class guarantees that the objects will have the same fields

Object Interaction Objects do not normally operate by themselves Objects can create other objects and invoke those object’s methods Most Java programs have objects that will do just this Question: How do we do this?

Source Code Like most programming languages, Java is written using plain text files or source code files The source code tells the program how objects are created and how the objects will interact After a source code file is written, it must be compiled so that the Java Virtual Machine (JVM) can interpret it

Return Values Some methods not only take parameters, but give something back to you. These methods are said to have a return value You can tell this in the signature –String getName() This methods returns a String –void moveRight() This method returns void (nothing)

Homework 1.2, 1.5, 1.6, 1.9, 1.11, 1.18, 1.26

Quiz Explain the difference between an object and a class.