Could Not Find Main Class - Program Will Exit

This is my first java program,i am using eclipse IDE-----

package day1.example;

public class MyFirstJava {

/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
System.out.println("hi");
}
}

When i saved it,it shows no error.when i run it then a pop-up says "could not find the main class.the program will exit" and in the console it says---

java.lang.UnsupportedClassVersionError: day1/example/MyFirstJava : Unsupported major.minor version 51.0
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(Unknown Source)
at java.security.SecureClassLoader.defineClass(Unknown Source)
at java.net.URLClassLoader.defineClass(Unknown Source)
at java.net.URLClassLoader.access$000(Unknown Source)

[Code] ......