ONE PIECE

[Visual Basic 6.0]
This example opens a shapefile as a feature class.
DE>
Public Sub OpenFeatureClass_Example()
  Dim pWorkspaceFactory As IWorkspaceFactory
  Set pWorkspaceFactory = New ShapefileWorkspaceFactory
  Dim pFeatureWorkspace As IFeatureWorkspace
  Set pFeatureWorkspace = _
    pWorkspaceFactory.OpenFromFile("D:\Data\Esridata\USA", 0)
  Dim pFeatureClass As IFeatureClass
  Set pFeatureClass = pFeatureWorkspace.OpenFeatureClass("States")
  MsgBox "There are " & pFeatureClass.FeatureCount(Nothing) & " states"
End SubDE>

[C#]
    //IFeatureWorkspace OpenFeatureClass Example
    //This example opens a shapefile as a feature class.
    //e.g., nameOfShapefile = "States";
    //      dataPath = "D:\\Data\\Esridata\\USA"
    public void IFeatureWorkspace_OpenFeatureClass_Example(string dataPath, string nameOfShapefile)
    {
        IWorkspaceFactory workspaceFactory = new ESRI.ArcGIS.DataSourcesFile.ShapefileWorkspaceFactoryClass();
        IFeatureWorkspace featureWorkspace = (IFeatureWorkspace)workspaceFactory.OpenFromFile(dataPath, 0);
        IFeatureClass featureClass = featureWorkspace.OpenFeatureClass(nameOfShapefile);
        Console.WriteLine("There are {0} features in the {1} feature class", featureClass.FeatureCount(new QueryFilterClass()), featureClass.AliasName);
    }
    //The generic form can be used with any type of workspace
    //e.g., nameOfFeatureClass = "States";
    //on ArcSDE use ISqlSyntax::QualifyTableName for fully qualified table names.
    public IFeatureClass getIFeatureClass(IWorkspace workspace, string nameOfFeatureClass)
    {
        //cast for the feature workspace from the workspace
        IFeatureWorkspace featureWorkspace = (IFeatureWorkspace)workspace;
        //open the featureclass
        return featureWorkspace.OpenFeatureClass(nameOfFeatureClass);
    }