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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

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