What does the "Invalid source release 1.7" error mean when using gradle for compilation?

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The "Invalid source release 1.7" error means that the version of Java being used by Gradle for compilation is lower than the required version. In this case, the code is written for Java 7, but the version being used for compilation by Gradle is lower than Java 7. This error can be resolved by upgrading the version of Java being used by Gradle to Java 7 or higher.