Java Code Compiles But Doesn't Run

In fact, I'm not yet past that "Hello World" program.I'm following the steps in "Head First: Java" book, and reached that point where one is ready to write his/her 1st Java code. Here's mine:

public class MyFirstApp
{
public static void main (String[] args)
{
System.out.println("I Rule!");
System.out.println("The World!");
}

}

As simple as it should be, and compiles fine producing the correspondent class. But it doesn't run, however, and spits the following execution-time errors:

Exception in thread "main" java.lang.UnsupportedClassVersionError: MyFirstApp : Unsupported major.minor version 51.0
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:643)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:277)

[code]...