What's the equivalence of StringBuffer (in Java) in DWT or D?

[Sam Hu]

Hello everybody!I was wondering what's the translation of StringBuffer in DWT or D,please refer to below codes in Java:
//********************************************

FileDialog dlg=new FileDialog(shell,SWT.MULTI);
String fn=dlg.open();
if(fn!=null)
{
     StringBuffer buf=new StringBuffer();
     String[] files=dlg.getFileName();
     for(int i=0,n=files.length;i<n;i++)
     {
       buf.append(dlg.getFilterPath());
       if(buf.charAt(buf.length()-1) !=File.separatorChar)
       {
           buf.append(File.separatorChar);
       }
       buf.append(files[i]);
       buf.append("  ");
       }
       // other operation....
}
//*******************************************
Can anybody help to the same implement in DWT,Thanks so much!!
Sam