java.lang.UnsupportedClassVersionError

Start a Java class and hits this java.lang.UnsupportedClassVersionError, what is class file version 52 56?

Error: A JNI error has occurred, please check your installation and try again
Exception in thread "main" java.lang.UnsupportedClassVersionError: 
TestHello has been compiled by a more recent version of the Java Runtime (class file version 56.0), 
this version of the Java Runtime only recognizes class file versions up to 52.0
        at java.lang.ClassLoader.defineClass1(Native Method)
        at java.lang.ClassLoader.defineClass(ClassLoader.java:763)
        at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
        at java.net.URLClassLoader.defineClass(URLClassLoader.java:468)
        at java.net.URLClassLoader.access$100(URLClassLoader.java:74)
        at java.net.URLClassLoader$1.run(URLClassLoader.java:369)
        at java.net.URLClassLoader$1.run(URLClassLoader.java:363)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:362)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:349)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
        at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:495)

Solution

Java version mismatch, this means that you compile the Java classes with JDK 12 (56) but try to run it in JDK 8 (52), read this from Wikipedia

Java SE 13 = 57 (0x39 hex)
Java SE 12 = 56 (0x38 hex)
Java SE 11 = 55 (0x37 hex)
Java SE 10 = 54 (0x36 hex)
Java SE 9 = 53 (0x35 hex)
Java SE 8 = 52 (0x34 hex)
Java SE 7 = 51 (0x33 hex)
Java SE 6.0 = 50 (0x32 hex)
Java SE 5.0 = 49 (0x31 hex)
JDK 1.4 = 48 (0x30 hex)
JDK 1.3 = 47 (0x2F hex)
JDK 1.2 = 46 (0x2E hex)
JDK 1.1 = 45 (0x2D hex)

To fix it, compile the Java classes with --release option, to target Java 8.

javac anyName.java --release 8

or Maven.

	<plugin>
		<groupId>org.apache.maven.plugins</groupId>
		<artifactId>maven-compiler-plugin</artifactId>
		<version>3.8.0</version>
		<configuration>
			<source>1.8</source>
			<target>1.8</target>
		</configuration>
	</plugin>