use :
HWND WINAPI FindWindow(
__in_opt LPCTSTR lpClassName,
__in_opt LPCTSTR lpWindowName
);
HWND WINAPI FindWindowEx(
__in_opt HWND hwndParent,
__in_opt HWND hwndChildAfter,
__in_opt LPCTSTR lpszClass,
__in_opt LPCTSTR lpszWindow
);
LRESULT WINAPI SendMessage(
__in HWND hWnd,
__in UINT Msg,
__in WPARAM wParam,
__in LPARAM lParam
);
with java using JNI.