Do not confuse Java applets with Java scripts. Scripts are snippets of code written in Java language and executed directly by the browser. Applets also pre-transferred in a cross-platform intermediate code and executed by the plugin. For speed of execution, applets are intermediate between scripts and programs in machine code.
Make sure the computer has the Java plug-in. To do this from another browser in which Java plug-in is guaranteed to be included, go to the following page:

Click the "Verify Java version".
If you find that a plugin is missing or it is outdated, download it from the following page:

There are versions of this plugin for various operating systems, including Linux and Windows the most common versions. The method of installation depends on Your operating system.
Launch the Opera browser and open the settings panel. To do this in older versions of the browser, select the menu item "Tools" - "Settings", and the new "Settings" - "General settings".
Open the "Advanced" tab and then on the left list select "Content".
Check "Enable Java". Tick the "Enable plug-ins" do not pay attention - it is designed to control other plugins, such as Flash. Click OK.
The Opera browser allows you to keep the Java plugin is enabled or disabled for all sites except those that specify otherwise. To adjust for a specific site, first select it, and then using the right mouse button open the context menu. Select "Settings for your site".
In the opened window choose tab "Content". Check or uncheck "Enable Java", and then click OK.