public class Copy
{public void DoWork(){ReadKeyboard reader = new ReadKeyboard();WritePrinter writer = new WritePrinter();string data = reader.ReadFromKeyboard();writer.WriteToPrinter(data);}
}

在我们要求向程序中添加更多读取器或写入器之前，此实现似乎非常好。在这种情况下，我们需要更改复制程序以适应新的读者和作家，并且需要编写条件语句，该条件语句将根据用途选择读者和作家，这违反了面向对象设计的“打开/关闭”原理。

public class Copy
{public void DoWork(){string data;switch (readerType){case  "keyboard":ReadKeyboard reader = new ReadKeyboard();data = reader.ReadFromKeyboard();break;case "scanner":ReadScanner reader2 = new ReadScanner();data = reader2.ReadFromScanner();break;}switch (writerType){case "printer":WritePrinter writer = new WritePrinter();writer.WriteToPrinter(data);break;case "flashdisk":WriteFlashDisk writer2 = new WriteFlashDisk();writer2.WriteToFlashDisk(data);break;}}
}

同样，如果您继续添加更多读取器或写入器，则我们需要更改复制程序的实现，因为复制程序取决于读取器和写入器的实现。

public interface IReader
{string Read();
}public interface IWriter
{void Write(string data);
}public class ReadKeyboard : IReader
{public string Read(){// code to read from keyboard and return as string}
}public class ReadScanner : IReader
{public string Read(){// code to read from scanner and return as string}
}public class WritePrinter : IWriter
{public void Write(string data){// code to write to the printer}
}public class WriteFlashDisk : IWriter
{public void Write(string data){// code to write to the flash disk}
}public class Copy
{private string _readerType;private string _writerType;public Copy(string readerType, string writerType){_readerType = readerType;_writerType = writerType;}public void DoWork(){IReader reader;IWriter writer;string data;switch (readerType){case  "keyboard":reader = new ReadKeyboard();break;case "scanner":reader = new ReadScanner();break;}switch (writerType){case "printer":writer = new WritePrinter();break;case "flashdisk":writer = new WriteFlashDisk();break;}data = reader.Read();writer.Write(data);}
}

在这种情况下，细节依赖于抽象，但高级类仍依赖于低级模块。在实例化高级模块范围内的低级模块对象时，高级模块仍然需要在添加新的低级组件时进行修改，这不能完全满足DIP。

public class Copy
{public void DoWork(){IReader reader = serviceLocator.GetReader();IWriter writer = serviceLocator.GetWriter();string data = reader.Read();writer.Write(data);}
}

高亮显示的代码替换了实例化读取器和写入器对象的逻辑。在这里，我们将控件创建从Copy程序（高级模块）转换为服务定位器。因此，copy无需通过添加/删除低级模块来更改程序。