Classes, Methods And Statements

Classes, Methods and Statements

Objectives “With regards to programming classes, methods and statements, C# offers what you would come to expect from a modern OOPL…”

• • • •

Classes Namespaces Methods Statements

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Part 1 •

Classes…

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The class is key •

In .NET, classes play a central role – every type is represented by a class – all data and code must reside within a class

public class App { public static void Main() { . . . } }

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public class Customer { . . . } public class Globals { . . . } public class Utility { . . . } 4

Part 2 •

Namespaces…

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Namespaces • •

The FCL contains thousands of classes… Inevitably, name collisions will occur – between classes in the FCL – between your classes and those in the FCL

•

Namespaces are a way to minimize collisions… – as well as logically organize our code

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Definition •

A namespace N is a set of names qualified by N namespace Workshop { public class Customer { . . . } public class Product { . . . } }//namespace

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Workshop.Custome r

Workshop.Produc t

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Example •

Framework Class Library (FCL) contains 1000's of classes – organized by namespaces

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FCL namespaces • •

FCL's outermost namespace is "System" FCL technologies nested within System… Namespace

Purpose

Assembly

System

Core classes, types

mscorlib.dll

System.Collections

Data structures

mscorlib.dll

System.Data

Database access

System.Data.dll

System.Windows.Forms

GUI

System.Windows.Forms.dll

System.XML

XML processing

System.Xml.dll

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Namespace != Assembly •

Orthogonal concepts: – namespace for logical organization – assembly for physical packaging

• •

You must reference an assembly in order to use it You can "import" a namespace to reduce typing…

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Fully-qualified references • A fully-qualified reference starts with the outermost namespace: System.Console.WriteLine("message");

• If you want, you can import a namespace & drop imported prefix – using directive allows you to import a namespace… using System; . . . Console.WriteLine("message");

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Complete example •

using directive(s) specified at top of file

/* main.cs */

namespace Workshop { public class Customer { . . . }

using System; using Workshop; public class App { public static void Main() { Customer c; c = new Customer("jim bag", 94652); Console.WriteLine( c.ToString() ); } }

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public class Product { . . . } }

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Point of clarification • •

using directive only includes types from specified namespace nested namespaces must be separately imported... /* main.cs */ using using using using using

System; System.Windows; System.Windows.Forms; System.Data; System.Data.OleDb;

public class App { . . . }

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Part 3 •

Methods…

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Types of methods •

Classes contain 2 types of methods: – subroutines with no return value (void) – functions with a return value (int, string, etc.)

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Methods may be: – instance – static

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Instance methods require an object to call Static methods are global and thus require only class name

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Example •

Array class in FCL – fully-qualified name is System.Array

instance method (absence of static)

namespace System { public class Array { public int GetUpperBound(int dimension) { ... } public static void Sort(Array a) { ... }

static method (presence of static)

. . . }

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}

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Calling methods •

Here's an example of calling into the Array class: /* main.cs */ using System; public class App { public static void Main() { int[] data = { 11, 7, 38, 55, 3 }; Array.Sort(data); for (int i=0; i<=data.GetUpperBound(0); i++) Console.WriteLine(i + ": " + data[i]); } }

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Parameter passing •

C# offers three options: – pass-by-value (default) – pass-by-reference – pass-by-result ("copy-out")

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More subtle than you might think…

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Case 1: pass-by-value with a value type •

Bits are copied… value

99

i

99

public class App

{

public static void Main() { int i = 99; Foo(i); System.Console.WriteLine(i); }

stack frame for Foo

stack frame for Main

Stack

// i = 99

private static void Foo(int value) { value = value + 1; } }

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Case 2: pass-by-ref with a value type •

Reference is passed… stack frame for Foo

value

public class App

{

i

public static void Main() { int i = 99; Foo(ref i); System.Console.WriteLine(i); }

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stack frame for Main

Stack

// i = 100

private static void Foo(ref int value) { value = value + 1; } }

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Case 3: pass-by-value with a reference type •

Reference is copied… A

public class App

{

public static void Main() Vals { Stack int[] Vals; Vals = new int[1000]; Vals[0] = 99; Foo2(Vals); System.Console.WriteLine(Vals[0]); // 100 }

array

private static void Foo2(int[] A) { A[0] = A[0] + 1; } }

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Case 4: pass-by-ref with a reference type •

Reference to reference is passed… A

public class App

{

public static void Main() Vals { Stack int[] Vals; Vals = new int[1000]; Vals[0] = 99; Foo2(ref Vals); System.Console.WriteLine(Vals[0]); // 100 }

array

private static void Foo2(ref int[] A) { A[0] = A[0] + 1; } }

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Case 5: pass-by-result? •

Pass-by-result is identical to pass-by-ref, except: – no value is passed in – result is copied back upon method return public class App

{

public static void Main() { int a, b; ComputeXYZ(out a, out b); System.Console.WriteLine("Results: " + a + ", " + b); } private static void ComputeXYZ(out int r1, out int r2) { r1 = ...; r2 = ...; } }

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Part 4 •

Statements…

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Statements in C# •

C# supports the standard assortment…

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Assignment Subroutine and function call Conditional – if, switch Iteration – for, while, do-while Control Flow – return, break, continue, goto

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Examples x = obj.foo(); if (x > 0 && x < 10) count++; else if (x == -1) ... else { ... while (x > 0) } { ... x--; }

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for (int k = 0; k < 10; k++) { ... }

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foreach •

Specialized foreach loop provided for collections like array – reduces risk of indexing error – provides read only access

int[] data = { 1, 2, 3, 4, 5 }; int sum = 0; foreac h

foreach (int x in data) { sum += x; } typ e

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valu e

collectio n

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Summary •

Standard OOP language support: – namespaces – classes – methods – statements

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Two types of methods – instance methods require an object to call – static methods are global and thus require only class name

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