Example Abstract Class

The abstract modifier is used in classes, methods and properties. Abstract modifier is used when you want the class to be a base class for other classes. Key points concerning abstract classes: • • • •

May not be instantiated. May contain abstract methods and accessors. Cannot be modified with the sealed modifier. A non-abstract class derived from an abstract class must include actual implementations of all the inherited abstract methods and accessors

You may use the abstract modifier in methods and properties to serve the same purpose of not having implementations of it. Key points concerning Abstract methods: • • •

It is implicitly a virtual method. May only be declared in abstract classes. There is no method body since there is no implementation of it during declaration. E.g. public abstract void GetUserInfo();

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// no {} after the signature

The actual implementation is provided by an overriding method which is of course of a non-abstract class. The following modifiers are not allowed in an abstract method declaration: static, virtual and override.

Abstract properties are similar to abstract methods except for declaration and invocation syntax. Key points concerning abstract properties: • •

May not be static An abstract inherited property can be overridden in a derived class by including a property declaration that uses the override method.

An abstract class has to provide implementations for all of its interface members. Sample: // Abstract classes using System; abstract class MyAbstractC // Abstract class { protected int iHours = 40; protected int iWage = 25; // A VB developer? *smirk* // Abstract method public abstract void DoOvertime(); // Abstract property public abstract int GetHours { get;

} // Abstract property public abstract int GetWage { get; } } // Derived from abstract class, MyAbstractC class MyDerivedC: MyAbstractC { // overriding the method public override void DoOvertime() { iHours = 50; iWage = 38; } // overriding the property public override int GetHours { get { return iHours; } } // overriding the property public override int GetWage { get { return iWage; } } public static void Main() { // instance of derived class MyDerivedC dC = new MyDerivedC(); dC.DoOvertime(); Console.WriteLine("Hours worked = {0}, Wage earned = {1}", dC.GetHours, dC.GetWage); // Pause output window Console.ReadLine(); } }

Output: Hours worked = 50, Wage earned = 38