java.lang.UnsupportedClassVersionError: org/jetbrains/kotlin/preloading/Preloader : Unsupported major.minor version 52.0 while compile kotlin

I am beginner in Kotlin. I am getting the following exception while doing following:

kotlinc sample.kt -include-runtime -d sample.jar

Exception in thread "main" java.lang.UnsupportedClassVersionError:
org/jetbrains/kotlin/preloading/Preloader : Unsupported major.minor
version 52.0
    at java.lang.ClassLoader.defineClass1(Native Method)
    at java.lang.ClassLoader.defineClass(ClassLoader.java:800)
    at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
    at java.net.URLClassLoader.defineClass(URLClassLoader.java:449)
    at java.net.URLClassLoader.access$100(URLClassLoader.java:71)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:361)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:425)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:358)
    at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:482)

Code

fun main(args: Array<String>){
      var a : Int
      a = getLength("Hello")
      println("length of word is $a")
  }
   
  fun getLength(word : Any) : Int? {
      if (word !is String) return null
      return word.length
  }

And kotlin version is Kotlin version 1.2.21-release-88 (JRE 1.7.0_79-b15)

JDK version which was used to build sample.jar is built with java version newr than one which you're using to compile kotlin file. You have 2 ways:

1. Rebuild sample jar with your current version of JDK
2. Update JDK on your computer and try compiling again