How to Solve \'java.lang.UnsupportedClassVersionError\' in Eclipse?

Diagnosing "java.lang.UnsupportedClassVersionError: Bad version number in .class file" in Eclipse

Developers encounter the infamous "UnsupportedClassVersionError" when attempting to include compiled code from open-source libraries. Despite verifying that both compilation and execution occur under the same JRE version, it persists.

Inspecting Project Properties

Eclipse utilizes its own compiler, allowing it to compile classes of a higher version than the installed JRE. To determine if this is the case, navigate to the project settings (Alt Enter) and the Java Compiler section.

Verifying Class Version Discrepancy

If the project compilation level is different from the JRE version, it can lead to this error. For instance, if the project compiles at Java 1.6 while the JRE is Java 1.5, the "UnsupportedClassVersionError" will occur. The screenshot provided in the reference material visually depicts this discrepancy (check the Java Compiler settings of the project in question).

Resolution

To rectify this issue, ensure that the project's compilation level matches that of the JRE installed on the system. This setting can be adjusted within the Eclipse project properties.

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