Generics

Generics

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Objectives


Objectives
• Learn how to create generic classes and
methods


Objectives
methods
• Understand the advantages and benefits of
generics


Objectives
methods
generics
• Explore the use of generics to sort and search in
arrays


Objectives
methods
generics
arrays
• See how to use generic interfaces and
constraints


Objectives
methods
generics
arrays
• See how to use generic interfaces and
constraints
• Explore the generic List class


Agenda


Agenda
• Introducing Generics


Agenda
• Generics and Arrays


Agenda
• Generic Interfaces


Agenda
• Generic Constraints


Agenda
• Generic Constraints
• Generics and Lists


Introducing Generics


• You should strive for code reuse


 Don’t write the same code repeatedly


o Put the code in a method and call the method repeatedly


 Don’t define the same methods repeatedly


o Put the methods in a class and use the class repeatedly


• Make your code as generic as possible


 Don’t write ten methods to handle ten different types


o Write one method that can handle multiple types


o Write one method that can handle multiple types
 Prior to Visual Studio 2005 you would use overloaded
methods or use objects


Generic Methods


Generic Methods
• Create a generic method that will perform the
same task for multiple data types


Generic Methods
• Use a type parameter to declare a generic class
or method


Generic Methods
or method
• Made possible with type parameters


Generic Methods
or method
 Placeholder for a specific data type


Generic Methods
or method
 Calling code decides, at runtime, what type it will
pass to the method


Generic Methods
or method
 Calling code decides, at runtime, what type it will
pass to the method
 Prohibits you from mixing data types


Generic Classes


Generic Classes
• Generic class has similar behavior to a generic
method, but at the class instance level


Generic Classes
• Each call to a method of the class must use the
same data type


Generic Classes
• Each call to a method of the class must use the
same data type
• Declare the class with a type parameter but not
the methods


Advantages of Generics


• Type-safety


• Type-safety
 Compiler enforces the requirement that you use a
specific data type


• Type-safety
specific data type
• Better performance


• Type-safety
specific data type
 No converting from objects to specific types


• Type-safety
specific data type
• Less code


• Type-safety
specific data type
• Less code
 Write a generic method once and pass to it any data
type


• Type-safety
specific data type
• Less code
type
• More flexible code


• Type-safety
specific data type
• Less code
type
• More flexible code
 Passing a different data type does not require new
code

Generics and Arrays


Generics and Arrays
• Arrays are a handy way to store a group of
related items


Generics and Arrays
related items
 Easily add or remove an item


Generics and Arrays
related items
 Easily add or remove an item
 Array class provides methods for sorting and
searching


Sorting Arrays


Sorting Arrays
• You can easily sort an array of simple data types


Sorting Arrays
• By default, you can’t sort an array of class
instances


Sorting Arrays
instances
 To sort an array, items must all be of the same type,
and that type must implement IComparable and
provide a CompareTo method


Sorting Arrays
instances
 To sort an array, items must all be of the same type,
and that type must implement IComparable and
provide a CompareTo method
 If the type does not implement IComparable, or if
an array contains multiple types, the sort fails at
runtime


Sorting with the IComparer Interface


• You can pass to Array.Sort an instance of a
class that implements IComparer


• You can pass to Array.Sort an instance of a
class that implements IComparer
• You need to provide a method named
Compare that compares two instances of the
same type


Sorting with Generic Comparisons


• Create a method that compares


 Accepts two parameters of the same type, matching
the type of data stored in the array


 Returns an integer value, representing the
comparison of the two parameters


• Pass the address of the method to Array.Sort


• Pass the address of the method to Array.Sort
• No need to implement IComparer


Searching with Generic Predicates


• Array.IndexOf returns an index of first
occurrence of a value in an array


 Works fine for simple data types but not for complex
data types


data types
• Create a method that defines a set of criteria
and determines whether an object meets those
criteria


data types
• Create a method that defines a set of criteria
and determines whether an object meets those
criteria
• Pass the address of the method to
Array.FindIndex


Generic Interfaces


Generic Interfaces
• Implement IComparable in your custom
classes


Generic Interfaces
classes
 You can sort the class using default Array.Sort


Generic Interfaces
classes
 You can sort the class using default Array.Sort
• Use the generic version of IComparable to
avoid the boxing and unboxing issues


Generic Constraints


Generic Constraints
• Use generic constraints to ensure that
parameters meet conditions


Generic Constraints
• Use generic constraints to ensure that
parameters meet conditions
 e.g., can only pass to a method type that implements
IComparable


Generics and Lists


Generics and Lists
• Classes can account for one-to-many
relationships


Generics and Lists
relationships
 Customers have Orders


Generics and Lists
relationships
• Create an Orders property in Customer class
and store instances of the Order class


Generics and Lists
relationships
• Can use an ArrayList


Generics and Lists
relationships
 ArrayList stores objects


Generics and Lists
relationships
• Use generic List class instead


Generics and Lists
relationships
• Use generic List class instead
 Similar capabilities as ArrayList plus type-safety and
better performance

Learn More!


Learn More!
• This is an excerpt from a larger course. Visit
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Generics

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