Java: Unsupported major.minor version 52.0

This error basically means that you compiled your Java code with the version higher than that on the target machine you are trying to run it on.

 $ java -versionjava version "1.8.0_20-ea"

Java 1.8 == 8 == 52 (go figure why this confusion)

J2SE 8 = 52,

J2SE 7 = 51, 

J2SE 6.0 = 50, 

J2SE 5.0 = 49, 

JDK 1.4 = 48, 

JDK 1.3 = 47, 

JDK 1.2 = 46, 

JDK 1.1 = 45

Solution 1: update Java version on target machine (often impossible)

Solution 2: compile with lower Java version (skip on fancy language features e.g. lambdas) 

e.g. using Maven

   <build>
      <plugins>
         <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.2</version>
            <configuration>
               <!-- target has java version "1.7.0_60", to be safe we use 1.6  -->
               <source>1.6</source>
               <target>1.6</target>
            </configuration>
         </plugin>

e.g. using Java Compiler

javac -target 1.6 HelloWorld.java