Other J/direct Features

by @dll.import the modifier (tag) within the boot command, you can also use the other two attributes of J/direct. The first item is a simplified access to the OLE function, and the second is the ANSI and Unicode version of the API function selection.

By convention, all OLE functions return a value of type HRESULT, which is a structured integer value defined by COM. If you write a program at the COM level and want to return something different from an OLE function, you must pass a special pointer to it-the memory area where the function will populate the data. In Java, however, we have no pointers available; Moreover, this method is not concise. With J/direct, we can use OLE modifiers in the @dll.import boot command to make it easy to call OLE functions. An intrinsic method that is marked as an OLE function is automatically converted to a COM-form function from the Java-form method signature, which determines the return type.

The second feature is the choice of ANSI or Unicode string control methods. Most of the Win32 API functions that control strings provide two versions. For example, suppose we look at the symbols exported by USER32.DLL, then we don't find a messagebox () function, instead we see the MessageBoxA () and MessageBoxW () functions-the ANSI and Unicode versions of the function respectively. If you don't specify which version to call in the @dll.import boot command, the JVM will try to decide for itself. However, this operation takes a long time to execute. Therefore, we generally can use Ansi,unicode or auto modifier hard rules.

For more detailed information about these features, refer to the technical documentation provided by Microsoft.