applet问题！

我做了一个打印单子的class，并封装成jar文件今天早上还好好的，下午重装了jvm环境！结果就抛出异常！大家帮我看看是什么问题啊？java.lang.NullPointerException at sun.plugin.net.proxy.PluginProxyManager.getProxyInfo(Unknown Source) at sun.plugin.net.protocol.http.HttpURLConnection.connectSetup(Unknown Source) at sun.plugin.net.protocol.http.HttpURLConnection.connect(Unknown Source) at sun.plugin.net.protocol.http.HttpURLConnection.getInputStream(Unknown Source) at sun.plugin.net.protocol.http.HttpUtils.followRedirects(Unknown Source) at sun.plugin.cache.CachedJarLoader.isUpToDate(Unknown Source) at sun.plugin.cache.CachedJarLoader.loadFromCache(Unknown Source) at sun.plugin.cache.CachedJarLoader.load(Unknown Source) at sun.plugin.cache.JarCache.get(Unknown Source) at sun.plugin.net.protocol.jar.CachedJarURLConnection.connect(Unknown Source) at sun.plugin.net.protocol.jar.CachedJarURLConnection.getJarFile(Unknown Source) at sun.misc.URLClassPath$JarLoader.getJarFile(URLClassPath.java:579) at sun.misc.URLClassPath$JarLoader.<init>(URLClassPath.java:542) at sun.misc.URLClassPath$3.run(URLClassPath.java:320) at java.security.AccessController.doPrivileged(Native Method) at sun.misc.URLClassPath.getLoader(URLClassPath.java:309) at sun.misc.URLClassPath.getLoader(URLClassPath.java:286) at sun.misc.URLClassPath.getResource(URLClassPath.java:156) at java.net.URLClassLoader$1.run(URLClassLoader.java:191) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:187) at sun.applet.AppletClassLoader.findClass(AppletClassLoader.java:143) at java.lang.ClassLoader.loadClass(ClassLoader.java:289) at sun.applet.AppletClassLoader.loadClass(AppletClassLoader.java:123) at java.lang.ClassLoader.loadClass(ClassLoader.java:235) at sun.applet.AppletClassLoader.loadCode(AppletClassLoader.java:561) at sun.applet.AppletPanel.createApplet(AppletPanel.java:617) at sun.plugin.AppletViewer.createApplet(Unknown Source) at sun.applet.AppletPanel.runLoader(AppletPanel.java:546) at sun.applet.AppletPanel.run(AppletPanel.java:298) at java.lang.Thread.run(Thread.java:534)