Java applet works in IDE, but not in browser

So I created a simple game that was working not too long ago. Recently, though, when I try to run it in any browser it just gives me a NullPointerException. The thread stack is as follows:

cache: Initialize resource manager: com.sun.deploy.cache.ResourceProviderImpl@18a270a
security: property package.access value sun.,com.sun.xml.internal.,com.sun.imageio.,com.sun.istack.internal.,com.sun.jmx.,com.sun.proxy.,com.sun.org.apache.bcel.internal.,com.sun.org.apache.regexp.internal.,com.sun.org.apache.xerces.internal.,com.sun.org.apache.xpath.internal.,com.sun.org.apache.xalan.internal.extensions.,com.sun.org.apache.xalan.internal.lib.,com.sun.org.apache.xalan.internal.res.,com.sun.org.apache.xalan.internal.templates.,com.sun.org.apache.xalan.internal.utils.,com.sun.org.apache.xalan.internal.xslt.,com.sun.org.apache.xalan.internal.xsltc.cmdline.,com.sun.org.apache.xalan.internal.xsltc.compiler.,com.sun.org.apache.xalan.internal.xsltc.trax.,com.sun.org.apache.xalan.internal.xsltc.util.,com.sun.org.apache.xml.internal.res.,com.sun.org.apache.xml.internal.serializer.utils.,com.sun.org.apache.xml.internal.utils.,com.sun.org.apache.xml.internal.security.,com.sun.org.glassfish.,org.jcp.xml.dsig.internal.,com.sun.java.accessibility.
security: property package.access new value sun.,com.sun.xml.internal.,com.sun.imageio.,com.sun.istack.internal.,com.sun.jmx.,com.sun.proxy.,com.sun.org.apache.bcel.internal.,com.sun.org.apache.regexp.internal.,com.sun.org.apache.xerces.internal.,com.sun.org.apache.xpath.internal.,com.sun.org.apache.xalan.internal.extensions.,com.sun.org.apache.xalan.internal.lib.,com.sun.org.apache.xalan.internal.res.,com.sun.org.apache.xalan.internal.templates.,com.sun.org.apache.xalan.internal.utils.,com.sun.org.apache.xalan.internal.xslt.,com.sun.org.apache.xalan.internal.xsltc.cmdline.,com.sun.org.apache.xalan.internal.xsltc.compiler.,com.sun.org.apache.xalan.internal.xsltc.trax.,com.sun.org.apache.xalan.internal.xsltc.util.,com.sun.org.apache.xml.internal.res.,com.sun.org.apache.xml.internal.serializer.utils.,com.sun.org.apache.xml.internal.utils.,com.sun.org.apache.xml.internal.security.,com.sun.org.glassfish.,org.jcp.xml.dsig.internal.,com.sun.java.accessibility.,com.sun.javaws,com.sun.deploy,com.sun.jnlp
security: property package.definition value sun.,com.sun.xml.internal.,com.sun.imageio.,com.sun.istack.internal.,com.sun.jmx.,com.sun.proxy.,com.sun.org.apache.bcel.internal.,com.sun.org.apache.regexp.internal.,com.sun.org.apache.xerces.internal.,com.sun.org.apache.xpath.internal.,com.sun.org.apache.xalan.internal.extensions.,com.sun.org.apache.xalan.internal.lib.,com.sun.org.apache.xalan.internal.res.,com.sun.org.apache.xalan.internal.templates.,com.sun.org.apache.xalan.internal.utils.,com.sun.org.apache.xalan.internal.xslt.,com.sun.org.apache.xalan.internal.xsltc.cmdline.,com.sun.org.apache.xalan.internal.xsltc.compiler.,com.sun.org.apache.xalan.internal.xsltc.trax.,com.sun.org.apache.xalan.internal.xsltc.util.,com.sun.org.apache.xml.internal.res.,com.sun.org.apache.xml.internal.serializer.utils.,com.sun.org.apache.xml.internal.utils.,com.sun.org.apache.xml.internal.security.,com.sun.org.glassfish.,org.jcp.xml.dsig.internal.,com.sun.java.accessibility.
security: property package.definition new value sun.,com.sun.xml.internal.,com.sun.imageio.,com.sun.istack.internal.,com.sun.jmx.,com.sun.proxy.,com.sun.org.apache.bcel.internal.,com.sun.org.apache.regexp.internal.,com.sun.org.apache.xerces.internal.,com.sun.org.apache.xpath.internal.,com.sun.org.apache.xalan.internal.extensions.,com.sun.org.apache.xalan.internal.lib.,com.sun.org.apache.xalan.internal.res.,com.sun.org.apache.xalan.internal.templates.,com.sun.org.apache.xalan.internal.utils.,com.sun.org.apache.xalan.internal.xslt.,com.sun.org.apache.xalan.internal.xsltc.cmdline.,com.sun.org.apache.xalan.internal.xsltc.compiler.,com.sun.org.apache.xalan.internal.xsltc.trax.,com.sun.org.apache.xalan.internal.xsltc.util.,com.sun.org.apache.xml.internal.res.,com.sun.org.apache.xml.internal.serializer.utils.,com.sun.org.apache.xml.internal.utils.,com.sun.org.apache.xml.internal.security.,com.sun.org.glassfish.,org.jcp.xml.dsig.internal.,com.sun.java.accessibility.,com.sun.javaws,com.sun.deploy,com.sun.jnlp
security: property package.access value sun.,com.sun.xml.internal.,com.sun.imageio.,com.sun.istack.internal.,com.sun.jmx.,com.sun.proxy.,com.sun.org.apache.bcel.internal.,com.sun.org.apache.regexp.internal.,com.sun.org.apache.xerces.internal.,com.sun.org.apache.xpath.internal.,com.sun.org.apache.xalan.internal.extensions.,com.sun.org.apache.xalan.internal.lib.,com.sun.org.apache.xalan.internal.res.,com.sun.org.apache.xalan.internal.templates.,com.sun.org.apache.xalan.internal.utils.,com.sun.org.apache.xalan.internal.xslt.,com.sun.org.apache.xalan.internal.xsltc.cmdline.,com.sun.org.apache.xalan.internal.xsltc.compiler.,com.sun.org.apache.xalan.internal.xsltc.trax.,com.sun.org.apache.xalan.internal.xsltc.util.,com.sun.org.apache.xml.internal.res.,com.sun.org.apache.xml.internal.serializer.utils.,com.sun.org.apache.xml.internal.utils.,com.sun.org.apache.xml.internal.security.,com.sun.org.glassfish.,org.jcp.xml.dsig.internal.,com.sun.java.accessibility.,com.sun.javaws,com.sun.deploy,com.sun.jnlp
security: property package.access new value sun.,com.sun.xml.internal.,com.sun.imageio.,com.sun.istack.internal.,com.sun.jmx.,com.sun.proxy.,com.sun.org.apache.bcel.internal.,com.sun.org.apache.regexp.internal.,com.sun.org.apache.xerces.internal.,com.sun.org.apache.xpath.internal.,com.sun.org.apache.xalan.internal.extensions.,com.sun.org.apache.xalan.internal.lib.,com.sun.org.apache.xalan.internal.res.,com.sun.org.apache.xalan.internal.templates.,com.sun.org.apache.xalan.internal.utils.,com.sun.org.apache.xalan.internal.xslt.,com.sun.org.apache.xalan.internal.xsltc.cmdline.,com.sun.org.apache.xalan.internal.xsltc.compiler.,com.sun.org.apache.xalan.internal.xsltc.trax.,com.sun.org.apache.xalan.internal.xsltc.util.,com.sun.org.apache.xml.internal.res.,com.sun.org.apache.xml.internal.serializer.utils.,com.sun.org.apache.xml.internal.utils.,com.sun.org.apache.xml.internal.security.,com.sun.org.glassfish.,org.jcp.xml.dsig.internal.,com.sun.java.accessibility.,com.sun.javaws,com.sun.deploy,com.sun.jnlp,org.mozilla.jss
security: property package.definition value sun.,com.sun.xml.internal.,com.sun.imageio.,com.sun.istack.internal.,com.sun.jmx.,com.sun.proxy.,com.sun.org.apache.bcel.internal.,com.sun.org.apache.regexp.internal.,com.sun.org.apache.xerces.internal.,com.sun.org.apache.xpath.internal.,com.sun.org.apache.xalan.internal.extensions.,com.sun.org.apache.xalan.internal.lib.,com.sun.org.apache.xalan.internal.res.,com.sun.org.apache.xalan.internal.templates.,com.sun.org.apache.xalan.internal.utils.,com.sun.org.apache.xalan.internal.xslt.,com.sun.org.apache.xalan.internal.xsltc.cmdline.,com.sun.org.apache.xalan.internal.xsltc.compiler.,com.sun.org.apache.xalan.internal.xsltc.trax.,com.sun.org.apache.xalan.internal.xsltc.util.,com.sun.org.apache.xml.internal.res.,com.sun.org.apache.xml.internal.serializer.utils.,com.sun.org.apache.xml.internal.utils.,com.sun.org.apache.xml.internal.security.,com.sun.org.glassfish.,org.jcp.xml.dsig.internal.,com.sun.java.accessibility.,com.sun.javaws,com.sun.deploy,com.sun.jnlp
security: property package.definition new value sun.,com.sun.xml.internal.,com.sun.imageio.,com.sun.istack.internal.,com.sun.jmx.,com.sun.proxy.,com.sun.org.apache.bcel.internal.,com.sun.org.apache.regexp.internal.,com.sun.org.apache.xerces.internal.,com.sun.org.apache.xpath.internal.,com.sun.org.apache.xalan.internal.extensions.,com.sun.org.apache.xalan.internal.lib.,com.sun.org.apache.xalan.internal.res.,com.sun.org.apache.xalan.internal.templates.,com.sun.org.apache.xalan.internal.utils.,com.sun.org.apache.xalan.internal.xslt.,com.sun.org.apache.xalan.internal.xsltc.cmdline.,com.sun.org.apache.xalan.internal.xsltc.compiler.,com.sun.org.apache.xalan.internal.xsltc.trax.,com.sun.org.apache.xalan.internal.xsltc.util.,com.sun.org.apache.xml.internal.res.,com.sun.org.apache.xml.internal.serializer.utils.,com.sun.org.apache.xml.internal.utils.,com.sun.org.apache.xml.internal.security.,com.sun.org.glassfish.,org.jcp.xml.dsig.internal.,com.sun.java.accessibility.,com.sun.javaws,com.sun.deploy,com.sun.jnlp,org.mozilla.jss
security: property package.access value sun.,com.sun.xml.internal.,com.sun.imageio.,com.sun.istack.internal.,com.sun.jmx.,com.sun.proxy.,com.sun.org.apache.bcel.internal.,com.sun.org.apache.regexp.internal.,com.sun.org.apache.xerces.internal.,com.sun.org.apache.xpath.internal.,com.sun.org.apache.xalan.internal.extensions.,com.sun.org.apache.xalan.internal.lib.,com.sun.org.apache.xalan.internal.res.,com.sun.org.apache.xalan.internal.templates.,com.sun.org.apache.xalan.internal.utils.,com.sun.org.apache.xalan.internal.xslt.,com.sun.org.apache.xalan.internal.xsltc.cmdline.,com.sun.org.apache.xalan.internal.xsltc.compiler.,com.sun.org.apache.xalan.internal.xsltc.trax.,com.sun.org.apache.xalan.internal.xsltc.util.,com.sun.org.apache.xml.internal.res.,com.sun.org.apache.xml.internal.serializer.utils.,com.sun.org.apache.xml.internal.utils.,com.sun.org.apache.xml.internal.security.,com.sun.org.glassfish.,org.jcp.xml.dsig.internal.,com.sun.java.accessibility.,com.sun.javaws,com.sun.deploy,com.sun.jnlp,org.mozilla.jss
security: property package.access new value sun.,com.sun.xml.internal.,com.sun.imageio.,com.sun.istack.internal.,com.sun.jmx.,com.sun.proxy.,com.sun.org.apache.bcel.internal.,com.sun.org.apache.regexp.internal.,com.sun.org.apache.xerces.internal.,com.sun.org.apache.xpath.internal.,com.sun.org.apache.xalan.internal.extensions.,com.sun.org.apache.xalan.internal.lib.,com.sun.org.apache.xalan.internal.res.,com.sun.org.apache.xalan.internal.templates.,com.sun.org.apache.xalan.internal.utils.,com.sun.org.apache.xalan.internal.xslt.,com.sun.org.apache.xalan.internal.xsltc.cmdline.,com.sun.org.apache.xalan.internal.xsltc.compiler.,com.sun.org.apache.xalan.internal.xsltc.trax.,com.sun.org.apache.xalan.internal.xsltc.util.,com.sun.org.apache.xml.internal.res.,com.sun.org.apache.xml.internal.serializer.utils.,com.sun.org.apache.xml.internal.utils.,com.sun.org.apache.xml.internal.security.,com.sun.org.glassfish.,org.jcp.xml.dsig.internal.,com.sun.java.accessibility.,com.sun.javaws,com.sun.deploy,com.sun.jnlp,org.mozilla.jss,com.sun.browser,com.sun.glass,com.sun.javafx,com.sun.media.jfxmedia,com.sun.media.jfxmediaimpl,com.sun.openpisces,com.sun.prism,com.sun.scenario,com.sun.t2k,com.sun.webpane,com.sun.pisces,com.sun.webkit
security: property package.definition value sun.,com.sun.xml.internal.,com.sun.imageio.,com.sun.istack.internal.,com.sun.jmx.,com.sun.proxy.,com.sun.org.apache.bcel.internal.,com.sun.org.apache.regexp.internal.,com.sun.org.apache.xerces.internal.,com.sun.org.apache.xpath.internal.,com.sun.org.apache.xalan.internal.extensions.,com.sun.org.apache.xalan.internal.lib.,com.sun.org.apache.xalan.internal.res.,com.sun.org.apache.xalan.internal.templates.,com.sun.org.apache.xalan.internal.utils.,com.sun.org.apache.xalan.internal.xslt.,com.sun.org.apache.xalan.internal.xsltc.cmdline.,com.sun.org.apache.xalan.internal.xsltc.compiler.,com.sun.org.apache.xalan.internal.xsltc.trax.,com.sun.org.apache.xalan.internal.xsltc.util.,com.sun.org.apache.xml.internal.res.,com.sun.org.apache.xml.internal.serializer.utils.,com.sun.org.apache.xml.internal.utils.,com.sun.org.apache.xml.internal.security.,com.sun.org.glassfish.,org.jcp.xml.dsig.internal.,com.sun.java.accessibility.,com.sun.javaws,com.sun.deploy,com.sun.jnlp,org.mozilla.jss
security: property package.definition new value sun.,com.sun.xml.internal.,com.sun.imageio.,com.sun.istack.internal.,com.sun.jmx.,com.sun.proxy.,com.sun.org.apache.bcel.internal.,com.sun.org.apache.regexp.internal.,com.sun.org.apache.xerces.internal.,com.sun.org.apache.xpath.internal.,com.sun.org.apache.xalan.internal.extensions.,com.sun.org.apache.xalan.internal.lib.,com.sun.org.apache.xalan.internal.res.,com.sun.org.apache.xalan.internal.templates.,com.sun.org.apache.xalan.internal.utils.,com.sun.org.apache.xalan.internal.xslt.,com.sun.org.apache.xalan.internal.xsltc.cmdline.,com.sun.org.apache.xalan.internal.xsltc.compiler.,com.sun.org.apache.xalan.internal.xsltc.trax.,com.sun.org.apache.xalan.internal.xsltc.util.,com.sun.org.apache.xml.internal.res.,com.sun.org.apache.xml.internal.serializer.utils.,com.sun.org.apache.xml.internal.utils.,com.sun.org.apache.xml.internal.security.,com.sun.org.glassfish.,org.jcp.xml.dsig.internal.,com.sun.java.accessibility.,com.sun.javaws,com.sun.deploy,com.sun.jnlp,org.mozilla.jss,com.sun.browser,com.sun.glass,com.sun.javafx,com.sun.media.jfxmedia,com.sun.media.jfxmediaimpl,com.sun.openpisces,com.sun.prism,com.sun.scenario,com.sun.t2k,com.sun.webpane,com.sun.pisces,com.sun.webkit
basic: Added progress listener: sun.plugin.util.ProgressMonitorAdapter@13b7c28
network: Cache entry not found [url: file:////files5.ad.lake.stark.k12.oh.us/shd/2015/15TROYERJONATHAN/Documents/Computer%20Science/Game/GUI.class, version: null]
network: Cache entry not found [url: file:////files5.ad.lake.stark.k12.oh.us/shd/2015/15TROYERJONATHAN/Documents/Computer%20Science/Game/, version: null]
security: Accessing keys and certificate in Mozilla user profile: null
network: Created version ID: 1.7.0.25
network: Created version ID: 1.7.0.25
security: SSV validation: running: 1.7.0_25, requested: null, range: null
network: Created version ID: 1.7.0.25
network: Created version ID: 1.7.0.25
security: continue with running version
network: Cache entry not found [url: file:////files5.ad.lake.stark.k12.oh.us/shd/2015/15TROYERJONATHAN/Documents/Computer%20Science/Game/ColorPanel.class, version: null]
basic: Applet loaded.
basic: Applet resized and added to parent container
basic: PERF: AppletExecutionRunnable - applet.init() BEGIN ; jvmLaunch dt 216867 us, pluginInit dt 217500 us, TotalTime: 434367 us
java.lang.NullPointerException
    at GUI.init(GUI.java:70)
    at com.sun.deploy.uitoolkit.impl.awt.AWTAppletAdapter.init(Unknown Source)
    at sun.plugin2.applet.Plugin2Manager$AppletExecutionRunnable.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)
basic: Removed progress listener: sun.plugin.util.ProgressMonitorAdapter@13b7c28
security: Reset deny session certificate store

Here's where the error is (at least as far as I can tell):

URL url=getCodeBase();
String u=url.toString();

The applet works fine when it is run in JCreator, but not in any browser or Adobe Dreamweaver. What does the thread stack mean?

I suppose that GUI is the the name of the class of your applet. (BTW, it should be nice if you had defined its package but it has not impact on this issue)

From the stacktrace in the traces you transmitted, I can also suppose that the two lines of code you put in your question are line 69 and 70.

I can thus suppose that getCodeBase() returns null so that the following line automatically leads to a NullPointerException (NPE). Starting from Java 7 update 25, getCodeBase() returns null when the applet is running from the local file system.

You should thus check if the value returned by getCodeBase() is null so your code could look like the following:

String u = "Some default value";
URL url=getCodeBase();
if(url != null) {
    u=url.toString();
}