How to: Explicitly Implement Interface Members (C# Programming Guide)

This example declares an interface, IDimensions, and a class, Box, which explicitly implements the interface members getLength and getWidth. The members are accessed through the interface instance dimensions.

Example

interface IDimensions
{
    float getLength();
    float getWidth();
}

class Box : IDimensions
{
    float lengthInches;
    float widthInches;

    Box(float length, float width)
    {
        lengthInches = length;
        widthInches = width;
    }
    // Explicit interface member implementation:  
    float IDimensions.getLength()
    {
        return lengthInches;
    }
    // Explicit interface member implementation: 
    float IDimensions.getWidth()
    {
        return widthInches;
    }

    static void Main()
    {
        // Declare a class instance box1:
        Box box1 = new Box(30.0f, 20.0f);

        // Declare an interface instance dimensions:
        IDimensions dimensions = (IDimensions)box1;

        // The following commented lines would produce compilation  
        // errors because they try to access an explicitly implemented 
        // interface member from a class instance:                    
        //System.Console.WriteLine("Length: {0}", box1.getLength());
        //System.Console.WriteLine("Width: {0}", box1.getWidth());

        // Print out the dimensions of the box by calling the methods  
        // from an instance of the interface:
        System.Console.WriteLine("Length: {0}", dimensions.getLength());
        System.Console.WriteLine("Width: {0}", dimensions.getWidth());
    }
}
/* Output:
    Length: 30
    Width: 20
*/

Robust Programming

• Notice that the following lines, in the Main method, are commented out because they would produce compilation errors. An interface member that is explicitly implemented cannot be accessed from a class instance:

  //System.Console.WriteLine("Length: {0}", box1.getLength());
  //System.Console.WriteLine("Width: {0}", box1.getWidth());
  

• Notice also that the following lines, in the Main method, successfully print out the dimensions of the box because the methods are being called from an instance of the interface:

  System.Console.WriteLine("Length: {0}", dimensions.getLength());
  System.Console.WriteLine("Width: {0}", dimensions.getWidth());
  

See Also

Tasks

How to: Explicitly Implement Members of Two Interfaces (C# Programming Guide)

Reference

Classes and Structs (C# Programming Guide)

Interfaces (C# Programming Guide)

Concepts

C# Programming Guide