Module 10 Encapsulating Data and Defining Overloaded Operators

Module 10 Encapsulating Data and Defining Overloaded Operators

Module Overview • Creating and Using Properties • Creating and Using Indexers • Overloading Operators

Lesson 1: Creating and Using Properties • What Is a Property? • Defining a Property • Automatic Properties • Instantiating an Object by Using Properties • Defining Properties in an Interface • Best Practices When Using Properties • Demonstration : Using Properties

What Is a Property? Method-like behavior Field-like syntax Property: get and set accessors Properties can provide: • Controlled access to data • Validation • Read/write control

Defining a Property Specify the access modifier Optionally specify an access modifier for the get or set accessor Specify the property type name private string my. String; public string My. String { get { return my. String; } private set { my. String = value; } } Add get and/or set accessors Use the value keyword in the set accessor to access the data passed to the property

Automatic Properties public string Name { get; set; } The automatic property shown above it converted by the compiler to code similar to: private string _name; public string Name { get { return _name; } set { this. _name = value; } } • Useful when you do not need to add custom logic to the property accessors • Must specify both get and set accessors • Important forward compatibility • No difference between automatic properties and normal properties to consuming applications

Instantiating an Object by Using Properties Employee john = new Employee { Name = "John" }; Employee louisa = new Employee() { Department = "Technical" }; Employee mike = new Employee { Name = "Mike", Department = "Technical" }; • An object initializer avoids problems with defining several constructors • A default constructor should instantiate properties to default values • A constructor is called the object initializer • A constructor is always run first, properties are set after so properties take precedence • An object initializer can use no brackets to call the default constructor, brackets with no parameters to explicitly call the default constructor, or brackets with parameters to call a nondefault constructor

Defining Properties in an Interface An interface is a contract between a type and a consuming application It does not contain implementation details Fields are considered implementation details; they cannot be defined in an interface Properties are not implementation details; they are data exposed for consumption so they can be defined in an interface Do not specify an interface IPerson { string Name { get; set; } int Age { get; } Date. Time Date. Of. Birth { set; } } Syntax the same as an automatic property; except you access do not have to specify modifier both accessors

Best Practices When Using Properties Only expose properties where they are appropriate! Bank. Account double Balance (get, set) ü Withdraw. Money(double Amount) ü Deposit. Money (double Amount) Would you let an application directly set a bank balance! Don’t add code to a get accessor that has any side effects on data Be careful to avoid accidentally recursive properties

Demonstration: Using Properties In this demonstration, you will: • Encapsulate data in a class by using properties • Add logic to the properties to prevent invalid data

Lab A: Creating and Using Properties • Exercise 1: Defining Properties in an Interface • Exercise 2: Implementing Properties in a Class • Exercise 3: Using Properties Exposed by a Class Logon information Virtual machine 10266 A-GEN-DEV User name Student Password Pa$$w 0 rd Estimated time: 25 minutes

Lab Scenario

Lab Review • What is the syntax for declaring a property in an interface? • What is the significant difference between automatic properties and nonautomatic properties? • What happens if you attempt to write to a property that exposes only a get accessor?

Lesson 2: Creating and Using Indexers • What Is an Indexer? • Creating an Indexer • Comparing Indexers and Arrays • Defining an Indexer in an Interface • Demonstration: Creating and Using an Indexer

What Is an Indexer? • Provides array-like syntax for accessing members in a set • Can use different subscripts to an array, for example, a string instead of an int • Can be overloaded Customer. Address. Book address. Book =. . . ; Address customer. Address = address. Book["a 2332"]; . . . customer. Address = address. Book[99];

Creating an Indexer The operator Specify the return Specify the parameters for should be public type the indexer public Customer this[string Customer. ID] { get { return database. Find. Customer(Customer. ID); } set { database. Update. Customer(Customer. ID, value); } } Use this keyword; all Add get and/or set accessors indexers must be called this to the indexer

Comparing Indexers and Arrays Subscripts Overloading Indexers Must use a numeric subscript to access individual members Can use nonnumeric subscripts, for example, strings to access individual members Cannot be overloaded in child classes Can be used as a normal parameter Method Parameters and a ref or out parameter Can only be used as a normal parameter; cannot be used as a ref or out parameter

Defining an Indexer in an Interface Indexers expose data to consuming classes; they are not considered implementation details. Therefore indexers can be added to an interface Do not interface IEmployee. Database { Employee this[string Name] { get; set; } } specify an access modifier As with a property, you do not have to specify both accessors Like all members of an interface, you can choose to implement indexers implicitly or explicitly

Demonstration: Creating and Using an Indexer In this demonstration, you will: • Add an indexer to a class • Use the indexer to access individual items in an array by specifying a name instead of an index

Lab B: Creating and Using Indexers • Exercise 1: Implementing an Indexer to Access Bits in a Control Register • Exercise 2: Using an Indexer Exposed by a Class Logon information Virtual machine 10266 A-GEN-DEV User name Student Password Pa$$w 0 rd Estimated time: 25 minutes

Lab Scenario

Lab Review • Can you overload an indexer in a child class? • What are some of the advantages of using an indexer in your class? • When can it be inappropriate to use an indexer in your class?

Lesson 3: Overloading Operators • What Is Operator Overloading? • Overloading an Operator • Restrictions When Overloading Operators • Best Practices When Overloading Operators • Implementing and Using Conversion Operators • Demonstration: Overloading an Operator

What Is Operator Overloading? - + / != Class My. Type {. . . }. . . My. Type var 1 =. . . ; My. Type var 2 =. . . ; . . . ? = var 1 + var 2; ==

Overloading an Operator The operator Use the operator should be public must be static keyword public static Hour operator +(Hour lhs, Hour rhs) { return new Hour(lhs. value + rhs. value); } Specify a return Specify which operator Specify the operands type you are overloading for the operator

Restrictions When Overloading Operators 1 • You cannot change the precedence or associativity of an operator 2 • You cannot change the multiplicity of an operator 3 • You cannot invent new operators (use methods instead) 4 • You cannot change the meaning of operators for built-in types 5 • You cannot overload all operators, for example, the dot (. ) operator 6 • You must define some operators in pairs (==, !=, etc)

Best Practices When Overloading Operators Define symmetric operators Do not modify operands ü ü public static Salary operator +(Salary salary, double number) { return new Salary(salary. amount + number); } public static Salary operator +(double number, Salary salary) { return salary + number; } Only define meaningful operators public static Bank. Account operator +(Bank. Account account, decimal amount) {. . . } public static Bank. Account operator -(Bank. Account account, decimal amount) {. . . }

Implementing and Using Conversion Operators Implicit conversion: No risk of data loss or exceptions Explicit conversion: Risk of data loss; requires a cast public static implicit operator int (Hour from) { return from. value; } public static void My. Method(int parameter) {. . . } public static void Main() { Hour lunch = new Hour(12); Example. My. Method(lunch); // implicit conversion } public static explicit operator Hour (int from) { return from. value; } public static void My. Other. Method(Hour parameter) {. . . } public static void Main() { int lunch = 12; Example. My. Other. Method((Hour)lunch); // explicit conversion }

Demonstration: Overloading an Operator In this demonstration, you will: • Overload the + operator in a class • Implement logic to add objects to an array by using the + operator

Lab C: Overloading Operators • Exercise 1: Defining the Matrix and Matrix. Not. Compatible. Exception Types • Exercise 2: Implementing Operators for the Matrix Type • Exercise 3: Testing the Operators for the Matrix Type Logon information Virtual machine 10266 A-GEN-DEV User name Student Password Pa$$w 0 rd Estimated time: 40 minutes

Lab Scenario

Lab Review • Can you declare an operator that is not static? • Can you change the multiplicity of an operator? • What must a binary operator do to support compound assignment statements?

Module Review and Takeaways • Review Questions • Best Practices