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52 lines
2.9 KiB
Markdown
Linux FAQs with Answers--How to change default Java version on Linux
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> **Question**: When I am trying to run a Java program on Linux, I am getting the following error. Looks like the Java program is compiled for a different Java version than the default Java program installed on my Linux. How can I switch the default Java version on Linux?
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>
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> Exception in thread "main" java.lang.UnsupportedClassVersionError: com/xmodulo/hmon/gui/NetConf : Unsupported major.minor version 51.0
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When a Java program is compiled, the build environment sets a "target" which is the oldest JRE version the program can support. If you run the Java program on a Linux system which does not meet the lowest JRE version requirement, you will encounter the following error while starting the program.
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Exception in thread "main" java.lang.UnsupportedClassVersionError: com/xmodulo/hmon/gui/NetConf : Unsupported major.minor version 51.0
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For example, in this case the program is compiled for Java JRE 1.7 but the system only has Java JRE 1.6.
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To solve this problem, you need to change the default Java version you are using to Java JRE 1.7 or higher (assuming that such JRE is already installed).
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First, **check available Java versions** on your Linux system by using update-alternatives command:
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$ sudo update-alternatives --display java
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In this example, there are four different Java versions that are installed: OpenJDK JRE 1.6, Oracle Java JRE 1.6, OpenJDK JRE 1.7 and Oracle Java JRE 1.7. The default Java version is currently set to OpenJDK JRE 1.6.
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If the necessary Java JRE is not installed, you can always install it using [these instructions][1].
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Now that there are suitable candidates to change to, you can **switch the default Java version** among available Java JREs by running the following command:
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$ sudo update-alternatives --config java
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When prompted, select the Java version you would like to use. In this example, we choose Oracle Java JRE 1.7.
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Now you can verify the default Java version as follows.
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$ java -version
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Finally, if you defined JAVA_HOME environment variable somewhere, update the variable according to the newly set default Java version.
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--------------------------------------------------------------------------------
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via: http://ask.xmodulo.com/change-default-java-version-linux.html
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作者：[Dan Nanni][a]
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译者：[译者ID](https://github.com/译者ID)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]:http://ask.xmodulo.com/author/nanni
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[1]:http://ask.xmodulo.com/install-java-runtime-linux.html |