CSE 1301 Lecture 3A: Using Classes and Object-Oriented Programming in C# - Prof. Briana Mo, Study notes of Computer Science

Download CSE 1301 Lecture 3A: Using Classes and Object-Oriented Programming in C# - Prof. Briana Mo and more Study notes Computer Science in PDF only on Docsity! CSE 1301 Lecture 3A Using Classes Figures from Lewis, “C# Software Solutions”, Addison Wesley Briana B. Morrison CSE 1301 3A-2 Topics • Class Basics and Benefits • Creating Objects • .NET Architecture and Base Class Libraries • Random Class • Math Class CSE 1301 3A-3 Object-Oriented Programming • Classes combine data and the methods (code) to manipulate the data • Classes are a template used to create specific objects • All C# programs consist of at least one class. CSE 1301 3A-4 Example • Student class – Data: name, year, and grade point average – Methods: store/get the value of each piece of data, promote to next year, etc. • Student Object: student1 – Data: Maria Gonzales, Sophomore, 3.5 CSE 1301 3A-5 Some Terminology • Object reference: identifier of the object • Instantiating an object: creating an object of a class • Instance of the class: the object • Methods: the code to manipulate the object data • Calling a method: invoking a service for an object. CSE 1301 3A-6 Class Data • Members of a class: the class's fields and methods • Fields: instance variables and class variables – Fields can be: • any primitive data type (int, double, etc.) • objects • Instance variables: variables defined in the class and given values in the object CSE 1301 3A-7 What’s in a Class Class contains Members are Fields Methods Instance variables Class variables CSE 1301 3A-8 Encapsulation • Instance variables are usually declared to be private, which means users of the class must reference the data of an object by calling methods of the class. • Thus the methods provide a protective shell around the data. We call this encapsulation. • Benefit: the class methods can ensure that the object data is always valid. CSE 1301 3A-9 Naming Conventions • Class names: start with a capital letter • Object references: start with a lowercase letter • In both cases, internal words start with a capital letter • Example: class: Student objects: student1, student2 CSE 1301 3A-10 1. Declare an Object Reference Syntax: ClassName objectReference; or ClassName objectRef1, objectRef2…; • Object reference holds address of object • Example: – Date d1; • d1 contains the address of the object, but the object hasn’t been created yet CSE 1301 3A-11 2. Instantiate an Object • Objects MUST be instantiated before they can be used • Call a constructor using new keyword • Constructor has same name as class. • Syntax: objectReference = new ClassName( arg list ); • Arg list (argument list) is comma-separated list of initial values to assign to object data, and may be empty CSE 1301 3A-12 Date Class API Constructor: special method that creates an object and assigns initial values to data Date Class Constructor Summary Date( ) creates a Date object with initial month, day, and year values of 1, 1, 2000 Date( int mm, int dd, int yy ) creates a Date object with initial month, day, and year values of mm, dd, and yy CSE 1301 3A-25 Dot Notation • Use when calling method to specify which object's data to use in the method • Syntax: objectReference.methodName( arg1, arg2, … ) • Note: no data types are specified in the method call; arguments are values only! CSE 1301 3A-26 Calling a Method CSE 1301 3A-27 • When calling a method, include only expressions in your argument list. Including data types in your argument list will cause a compiler error. • If the method takes no arguments, remember to include the empty parentheses after the method's name. The parentheses are required even if there are no arguments. CSE 1301 3A-28 .NET Architecture • Framework • When you press F5 – source code compiled into IL – submitted to .NET engine for execution CSE 1301 3A-29 CSE 1301 3A-30 Base Class Libraries • Need to become familiar with libraries to use most efficiently • Group services under Namespace • Most commonly accessed Namespaces are grouped under System Namespace CSE 1301 3A-31 using Declaration • Must have using statement to use values in library: using System.Text; • Or you can fully qualify: System.Text.StringBuilder phrase = new System.Text.StringBuilder (“Change is inevitable”); CSE 1301 3A-32 CSE 1301 3A-33 Random Class • To generate random numbers • Generates a pseudorandom number (appearing to be random, but mathematically calculated based on seed value) 3-33 CSE 1301 3A-34 Random API 3-34 CSE 1301 3A-35 3-35 To generate a random integer between a and up to, but not including, b: CSE 1301 3A-36 3-36 CSE 1301 3A-37 Math Class • Basic mathematical functions • All methods are static methods (class methods) – invoked through the name of the class – no need to instantiate object • Two static constants – PI = the value of pi – E = the base of the natural logarithm 3-37 CSE 1301 3A-38 Calling static Methods • Use dot syntax with class name instead of object reference • Syntax: ClassName.methodName( args ) • Example: int absValue = Math.Abs( -9 ); • abs is a static method of the Math class that returns the absolute value of its argument (here, -9). 3-38 CSE 1301 3A-39 3-39 CSE 1301 3A-40 3-40 CSE 1301 3A-41 3-41 CSE 1301 3A-42 Summary • What did you learn? • Muddiest Point