JAVA中isEmpty和null以及""的区别

public partial class WebForm4 : System.Web.UI.Page
{
private WebBrowser _myWebBrowser;
protected void Page_Load(object sender, EventArgs e)
{
string url = "www.163.com";
_myWebBrowser = new WebBrowser();
_myWebBrowser.ScrollBarsEnabled = false;
_myWebBrowser.Navigate(url);
_myWebBrowser.DocumentCompleted += new WebBrowserDocumentCompletedEventHandler(_myWebBrowser_DocumentCompleted);
while (_myWebBrowser.ReadyState != WebBrowserReadyState.Complete)
{
System.Windows.Forms.Application.DoEvents();
}

}

void _myWebBrowser_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
{
_myWebBrowser.Width = _myWebBrowser.Document.Body .ScrollRectangle.Width;
_myWebBrowser.Height = _myWebBrowser .Document .Body .ScrollRectangle .Height;
using (Bitmap bmp = new Bitmap(_myWebBrowser.Width, _myWebBrowser.Height))
{
_myWebBrowser.DrawToBitmap(bmp, new Rectangle(0, 0, bmp.Width, bmp.Height));
bmp.Save("c:\\2.png", ImageFormat.Png);

}
}
}