Lecture_03 - ENGR 2200U UOIT/FEAS Fall 2007 ENGR 2710U OO...

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ENGR 2200U UOIT/FEAS Fall 2007 © Mike Eklund ENGR 2710U OO Programming and Design 1 Implementing Classes Implementing Classes Professor Saman Kumarawadu ENGR 2710U Fall 2010 – Saman Kumarawadu ENGR 2710U OO Programming and Design Chapter Goals • To become familiar with the process of implementing classes • To be able to implement simple methods • To understand the purpose and use of constructors • To understand how to access instance fields and local variables • To appreciate the importance of documentation comments
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ENGR 2200U UOIT/FEAS Fall 2007 © Mike Eklund ENGR 2710U OO Programming and Design Instance Variables • An object stores its data in instance variables • An instance of a class is an object of the class. • Instance variable is a storage location of each object of the class. • Instance variable declaration includes: • An access specifier • Type of the instance variable • The name of the instance variable ENGR 2710U OO Programming and Design Syntax 3.1: Instance Variable Declaration Syntax accessSpecifier class ClassName { accessSpecifier typeName variableName; ………. . } Example: public class Counter { private int value; } Instance variable is always private Each object of this class has separate copy of this instance variable
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ENGR 2200U UOIT/FEAS Fall 2007 © Mike Eklund ENGR 2710U OO Programming and Design Instance Variables: Example public class Student { private String name; // Student's name. private double test1, test2, test3; // Grades on three tests. public double getAverage() { // compute average test grade return (test1 + test2 + test3) / 3; } } // end of class Student Special statement that terminates the method call and return a result to the method’s caller. ENGR 2710U OO Programming and Design Student std, std1,std2, std3; // Declare four variables type Student. std = new Student(); // Create a new object belonging to Student class and store a reference to that object in the variable std. std1 = new Student(); // Create a second Student object and store a reference to it in the variable std1. std2 = std1; // Copy the reference value in std1 into the variable std2. std3 = null; // Store a null reference in the variable std3. std.name = "John Smith"; // Set values of some instance variables. std1.name = "Mary Jones"; // (Other instance variables have default initial values of zero.)
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UOIT/FEAS Fall 2007 © Mike Eklund ENGR 2710U OO Programming and Design Access specifier private • The variables defined with access specifier private can be accessed only by the methods in the same class, but not by any other methods. • Hiding instance variables by making them private Continued… ENGR 2710U OO Programming and Design Encapsulation • A black box: electronic control module of a car • Hides its inner workings Encapsulation: the process of hiding implementation details while publishing an interface • What is the right concept for each particular black box? Continued…
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This note was uploaded on 11/10/2010 for the course PROGRAMMIN 2860U taught by Professor Saman during the Fall '10 term at UOIT.

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Lecture_03 - ENGR 2200U UOIT/FEAS Fall 2007 ENGR 2710U OO...

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