Time to time it might happen that you need to know which version the class files were compiled for. Or to be more specific what target were specified while running javac compiler. As target specifies VM version the classes were generated for. This can be specified in maven as follows:

<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<target>1.6</target>
</configuration>
</plugin>

It is not a rocket science, right. To find out the version the code were generated for we use javap (java class file disassembler). The following line do the trick:

javap -verbose -classpath versiontest-1.0.jar cz.test.string.StringPlaying

Compiled from "StringPlaying.java"
public class cz.test.string.StringPlaying extends java.lang.Object
SourceFile: "StringPlaying.java"
minor version: 0
major version: 50
Constant pool:
const #1 = Method       #12.#28;        //  java/lang/Object."<init>":()V
const #2 = String       #29;            //  beekeeper
const #3 = Method       #30.#31;        //  java/lang/String.substring:(II)Ljava/lang/String;

Major version matches java version based on following table

Table taken from Oracle blog