function openCenteredWindow(url, height, width, name, parms) {
var left = Math.floor( (screen.width - width) / 2);
var top = Math.floor( (screen.height - height) / 2);
var winParms = "top=" + top + ",left=" + left + ",height=" + height + ",width=" + width;
if (parms) { winParms += "," + parms; }
var win = window.open(url, name, winParms);
if (parseInt(navigator.appVersion) >= 4) { win.window.focus(); }
return win;
}

Java kodcularının bilgiği kolay bir kod.