Several copies of Java can be installed on the same computer, and if you have several browsers, each of them may use a different version or not at all. This article describes several ways to check this.
Steps
Method 1 of 4: Check Online

Step 1. Open a new window in your browser and click here to go to the Java site
Oracle, the developer of the Java Platform, has created a simple page that checks your Java installed and reports the exact version. This can be done from any operating system.

Step 2. First, click the "Check Java version" button

Step 3. When prompted by your browser security software, let Java confirm the version

Step 4. Check the results in a few seconds
These will include the version number and the update number. The version number is most important if you are checking compatibility with other programs.
Method 2 of 4: Windows

Step 1. Press the keyboard shortcut windows + r and enter "cmd" and in the command line that opens, enter java -version
The result will look something like this: Java version "1.6.0_03 Java (TM) SE Runtime Environment (build 1.6.0_03-b05) Java HotSpot (TM) Client VM (build 1.6.0_03-b05, mixed mode, sharing).

Step 2. On a computer that does not have any version of Java from Sun Microsystems installed, this will result in an error message
'java' is not recognized as an internal or external command, operable program or batch file.

Step 3. A computer that has only a very old version of Java from Microsoft installed will have the same error message
On a machine with multiple Java versions, this command will return the default JVM version.
Method 3 of 4: Mac OSX

Step 1. Open the Hard Disk located on the Desktop OR you can click the search menu and open Applications

Step 2. In the Hard Disk window go to Applications, then to Utilities

Step 3. In Utilities open Terminal and in Terminal type "java -version" and get the current version of java
Method 4 of 4: Linux

1 Open a terminal window and type "java -version"
This command should return something like: Java (TM) 2 Runtime Environment, Standard Edition (build 1.6) If it returns -bash: java: command not found, it means either java is not installed or you did not specify the path correctly

Step 2. Use free internet testers, go here and click the Check Java version button
Follow this link
- In Firefox 3, go to Tools, click on the Add-ons button and go to the Plugins tab.
- For Firefox 2 or 3: For Firefox versions 2 and 3, enter: about: plugins in the address bar. If Java is installed, there will be multiple Java entries.
- In Internet Explorer 7 or 8, go to Tools, select Internet Options and on the General tab, click on the History Settings button, click the Show Objects button, right-click on the ActiveX control and view its properties. Each ActiveX control has a "base code" and for each of the Java controls it will display a version number