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I'm having trouble running Java; I keep getting a ClassNotFoundException error.

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  • Nzaghachi ikpeazụ nke AGhosh

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After updating to the latest version of Java (7.10), I'm unable to run Java at all. When detecting Java (http://java.com/en/download/testjava.jsp), I receive an error message and when I click, it says there is a ClassNotFoundException error. I've tried reinstalling Firefox, reinstalling this version of Java and a few older versions, trying Chrome and IE9, and in all cases, I've run into the same issue. On my add-ons, it appears like normal, and the installation works fine. Both:

  • Next Generation Java Plug-in 10.10.2 for Mozilla browsers
  • NPRuntime Script Plug-in Library for Java(TM) Deploy

Are enabled, alongside Browser Settings on the Java control settings, and I've cleared the cache as well. I've tried all the relevant fixes on http://java.com/en/download/testjava.jsp. I have absolutely no idea what to do. I've tried everything. Do any of you have suggestions?

After updating to the latest version of Java (7.10), I'm unable to run Java at all. When detecting Java (http://java.com/en/download/testjava.jsp), I receive an error message and when I click, it says there is a ClassNotFoundException error. I've tried reinstalling Firefox, reinstalling this version of Java and a few older versions, trying Chrome and IE9, and in all cases, I've run into the same issue. On my add-ons, it appears like normal, and the installation works fine. Both: * Next Generation Java Plug-in 10.10.2 for Mozilla browsers * NPRuntime Script Plug-in Library for Java(TM) Deploy Are enabled, alongside Browser Settings on the Java control settings, and I've cleared the cache as well. I've tried all the relevant fixes on http://java.com/en/download/testjava.jsp. I have absolutely no idea what to do. I've tried everything. Do any of you have suggestions?

Asịsa ahọpụtara

Hey all, I just wanted to post the solution I came to. I found another thread which solved my problem (https://forums.oracle.com/thread/2397610), in specific the last post. It boils down to this line:

"I have used the above trick of adding in control panel / Java / Java / View / Runtime parameters the value -Djava.net.preferIPv4Stack=true for my 2 JRE then saved then restarted my browser and suddenly it worked.*".

It suddenly worked for me too. Good luck!

Gụọ azịza a na nghọta 👍 0

All Replies (7)

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Try to clear the Java cache.

Control Panel > Java > General tab > "Temporary Internet Files" > Settings > Delete Files

  • C:\Users\<user>\AppData\LocalLow\Sun\Java\Deployment\cache\

If that doesn't help then try to uninstall and reinstall 32 bit Java.

You can also look at this program to uninstall Java:

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I've tried both.

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Try to boot the computer in Windows Safe mode with network support (press F8 on the boot screen) as a test to see if that helps in case some security software is interfering.

You can also try to uninstall the current Java 7 version and install the latest Java 6 version.

You can find the latest Java version on the Oracle website.

See Java Platform > Java SE 7U10 or Java 6U38 (Download JRE)

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I have tried all of the above and still cannot get Java to work. do you have any other suggestions?

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I cannot send out any email. Only receive it. HELP! I am desperate!

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Hi p53colbert

Could you please start a new thread instead of posting in an existing thread?

Then you can provide more information like your operating system and installed extensions and installed plugins.


Make sure to have a 32 bit Java version in case you are on a 64 bit Windows platform.

Do you see the Java plugin in Tools > Add-ons > Plugins ?

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Asịsa Ahọpụtara

Hey all, I just wanted to post the solution I came to. I found another thread which solved my problem (https://forums.oracle.com/thread/2397610), in specific the last post. It boils down to this line:

"I have used the above trick of adding in control panel / Java / Java / View / Runtime parameters the value -Djava.net.preferIPv4Stack=true for my 2 JRE then saved then restarted my browser and suddenly it worked.*".

It suddenly worked for me too. Good luck!