CHARLES UNIVERSITY IN PRAGUE faculty of mathematics and physics C# Language &.NET Platform 4 th...

CHARLES UNIVERSITY IN PRAGUE

http://d3s.mff.cuni.cz/~jezek

faculty of mathematics and physics

C# Language & .NET Platform

4th Lecture

Pavel Ježekpavel.jezek@d3s.mff.cuni.cz

Some of the slides are based on University of Linz .NET presentations.© University of Linz, Institute for System Software, 2004

published under the Microsoft Curriculum License(http://www.msdnaa.net/curriculum/license_curriculum.aspx)

CLI Type SystemAll types

Reference types(allocated on

managed heap)

PointersValue types(allocated in-place

[with exceptions])

Classes(e.g. strings)

Interfaces Arrays Delegates

Simple types(Int32, Int64,

Double, Boolean, Char, …)

Nullables

EnumerationsStructures

User defined structures

Visibility

Visibility modifiers:public Access is not restricted.

protected Access is limited to the containing class or types derived from the containing class.

internal Access is limited to the current assembly.

protected internal Access is limited to the current assembly or types derived from the containing class.

private Access is limited to the containing type.

Default visibility in:enum publicclass privateinterface publicstruct private

CLI Type SystemAll types

Reference types(allocated on

managed heap)

PointersValue types(allocated in-place

[with exceptions])

Classes(e.g. strings)

Interfaces Arrays Delegates

Simple types(Int32, Int64,

Double, Boolean, Char, …)

Nullables

EnumerationsStructures

User defined structures

Parameters

value parameters (input parameters)void Inc(int x) {x = x + 1;}void f() {int val = 3;Inc(val); // val == 3}

- "call by value"- formal parameter is a copy of the

actual parameter- actual parameter is an expression

- "call by reference"- formal parameter is an alias for the

actual parameter(address of actual parameter is passed)

- actual parameter must be a variable

ref parameters (transient parameters)void Inc(ref int x) { x = x + 1; }void f() {

int val = 3;Inc(ref val); // val == 4

}

Parameters

value parameters (input parameters)void Inc(int x) {x = x + 1;}void f() {int val = 3;Inc(val); // val == 3}

- "call by value"- formal parameter is a copy of the

actual parameter- actual parameter is an expression

- similar to ref parametersbut no value is passed by the caller.

- must not be used in the method beforeit got a value.

out parameters (output parameters)void Read (out int first, out int next) {

first = Console.Read();next = Console.Read();

}void f() {

int first, next;Read(out first, out next);

}

- "call by reference"- formal parameter is an alias for the

actual parameter(address of actual parameter is passed)

- actual parameter must be a variable

ref parameters (transient parameters)void Inc(ref int x) { x = x + 1; }void f() {

int val = 3;Inc(ref val); // val == 4

}

CLI Type SystemAll types

Reference types(allocated on

managed heap)

PointersValue types(allocated in-place

[with exceptions])

Classes(e.g. strings)

Interfaces Arrays Delegates

Simple types(Int32, Int64,

Double, Boolean, Char, …)

Nullables

EnumerationsStructures

User defined structures

Declaration of Local Variables

void foo(int a) {int b;if (...) {

int b; // error: b is already declared in the outer blockint c;int d;...

} else {int a; // error: a is already declared in the outer block (parameter)int d; // ok: no conflict with d in the if block

}for (int i = 0; ...) {...}for (int i = 0; ...) {...} // ok: no conflict with i from the previous loopint c; // error: c is already declared in a nested block

}

int e = 1, f;if (e == 1) {

f = 2;}e = f; // error: f is not initialized in every possible execution path

CLI Type SystemAll types

Reference types(allocated on

managed heap)

PointersValue types(allocated in-place

[with exceptions])

Classes(e.g. strings)

Interfaces Arrays Delegates

Simple types(Int32, Int64,

Double, Boolean, Char, …)

Nullables

EnumerationsStructures

User defined structures

How Would You Implement List<T>.Clear()?

Option Complexity with Respect to Number of Elements in List (n)

A O(1)

B O(n)

C Something else.

How Would You Implement List<T>.Clear()?

Option Complexity with Respect to Number of Elements in List (n)

A O(1)

B O(n) – set all elements to null! Mind the GC!C Something else.

What about String.Substring?

CLI Type SystemAll types

Reference types(allocated on

managed heap)

PointersValue types(allocated in-place

[with exceptions])

Classes(e.g. strings)

Interfaces Arrays Delegates

Simple types(Int32, Int64,

Double, Boolean, Char, …)

Nullables

EnumerationsStructures

User defined structures

CLI Type InheritanceSystem.Object(C# keyword: object)

user-defined classes(C# keyword: class)

delegates(C# keyword: delegate)

pointers(C#: Type *)

System.Delegate

System.MulticastDelegate

System.ValueType

System.Enum

System.Array

arrays(C#: Type[] or Type[,])

System.String(C# keyword: string)

interfaces(C# keyword: interface)

user-defined structures

(C# keyword: struct)

enumerations(C# keyword: enum)

System.Int32(C# keyword: int)

System.Int64(C# keyword: long)

System.Double(C# keyword: double)

System.Boolean(C# keyword: bool)

…

simple types

System.Nullable(C#: Type?)

CLI Type InheritanceSystem.Object(C# keyword: object)

user-defined classes(C# keyword: class)

delegates(C# keyword: delegate)

pointers(C#: Type *)

System.Delegate

System.MulticastDelegate

System.ValueType

System.Enum

System.Array

arrays(C#: Type[] or Type[,])

System.String(C# keyword: string)

interfaces(C# keyword: interface)

user-defined structures

(C# keyword: struct)

enumerations(C# keyword: enum)

System.Int32(C# keyword: int)

System.Int64(C# keyword: long)

System.Double(C# keyword: double)

System.Boolean(C# keyword: bool)

…

simple types

System.Nullable(C#: Type?)

Interfaces are not inherited from System.Object, but

System.Object members are callable/accessible via any interface

type expression.

Visibility

Visibility modifiers:public Access is not restricted.

protected Access is limited to the containing class or types derived from the containing class.

internal Access is limited to the current assembly.

protected internal Access is limited to the current assembly or types derived from the containing class.

private Access is limited to the containing type.

Default visibility in:enum publicclass privateinterface publicstruct private

Example: Inheritance of private members

CLI Type InheritanceSystem.Object(C# keyword: object)

user-defined classes(C# keyword: class)

delegates(C# keyword: delegate)

pointers(C#: Type *)

System.Delegate

System.MulticastDelegate

System.ValueType

System.Enum

System.Array

arrays(C#: Type[] or Type[,])

System.String(C# keyword: string)

interfaces(C# keyword: interface)

user-defined structures

(C# keyword: struct)

enumerations(C# keyword: enum)

System.Int32(C# keyword: int)

System.Int64(C# keyword: long)

System.Double(C# keyword: double)

System.Boolean(C# keyword: bool)

…

simple types

System.Nullable(C#: Type?)

CLI Type Inheritance (Sealed Types)System.Object(C# keyword: object)

user-defined classes(C# keyword: class)

delegates(C# keyword: delegate)

pointers(C#: Type *)

System.Delegate

System.MulticastDelegate

System.ValueType

System.Enum

System.Array

arrays(C#: Type[] or Type[,])

System.String(C# keyword: string)

interfaces(C# keyword: interface)

user-defined structures

(C# keyword: struct)

enumerations(C# keyword: enum)

System.Int32(C# keyword: int)

System.Int64(C# keyword: long)

System.Double(C# keyword: double)

System.Boolean(C# keyword: bool)

…

simple types

System.Nullable(C#: Type?)

sealed

sealedsealed

sealed

sealed

sealed

sealed

Optionally sealed

Ref. Type DOES NOT Imply InstancesSystem.Object(C# keyword: object)

user-defined classes(C# keyword: class)

delegates(C# keyword: delegate)

pointers(C#: Type *)

System.Delegate

System.MulticastDelegate

System.ValueType

System.Enum

System.Array

arrays(C#: Type[] or Type[,])

System.String(C# keyword: string)

interfaces(C# keyword: interface)

user-defined structures

(C# keyword: struct)

enumerations(C# keyword: enum)

System.Int32(C# keyword: int)

System.Int64(C# keyword: long)

System.Double(C# keyword: double)

System.Boolean(C# keyword: bool)

…

simple types

System.Nullable(C#: Type?)

Hiding

Members can be declared as new in a subclass.They hide inherited members with the same name and signature.

class A {public int x;public void F() {...}public virtual void G() {...}}

class B : A {public new int x;public new void F() {...}public new void G() {...}}

B b = new B();b.x = ...; // accesses B.xb.F(); ... b.G(); // calls B.F and B.G

((A)b).x = ...; // accesses A.x!((A)b).F(); ... ((A)b).G(); // calls A.F and A.G!

What is the output the following program?

class A {public string className = “A”;

}class B : A {

private string className = “B”;}class Program {

static void Main(string[] args) {Console.WriteLine(new B().className);

}}

Option Result

A It will not compile – error in class B.

B It will not compile – error in class Program.

C A

D B

E It will generate a runtime error.

What is the output the following program?

class A {public string className = “A”;

}class B : A {

private string className = “B”;}class Program {

static void Main(string[] args) {Console.WriteLine(new B().className);

}}

Option Result

A It will not compile – error in class B.

B It will not compile – error in class Program.

C A

D B

E It will generate a runtime error.

a compiler warning: use new keyword

new

What is the output the following program?

class A {public string className = “A”;

}class B : A {

private string className = “B”;}class Program {

static void Main(string[] args) {Console.WriteLine(new B().className);

}}

Option Result

A It will not compile – error in class B.

B It will not compile – error in class Program.

C A & a compiler warning: use new keyword.

D B

E It will generate a runtime error.

What is the output the following program?

class A {public string className = “A”;

}class B : A {

private string className = “B”;public void f() {

Console.WriteLine(className);}

}class Program {

static void Main(string[] args) {Console.Write(new B().className);new B().f();

}}

Option Result

A A A

B A B

C B A

D B B

What is the output the following program?

class A {public string className = “A”;

}class B : A {

private string className = “B”;public void f() {

Console.WriteLine(className);}

}class Program {

static void Main(string[] args) {Console.Write(new B().className);new B().f();

}}

Option Result

A A A

B A B & a compiler warning: use new keyword.

C B A

D B B