Error while running program: Unsupported major.minor version 52.0 [closed]

While running my program I'm getting this error:

Exception in thread "main" java.lang.UnsupportedClassVersionError: TestaContador : Unsupported major.minor version 52.0
    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$100(Unknown Source)
    at java.net.URLClassLoader$1.run(Unknown Source)
    at java.net.URLClassLoader$1.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    at sun.launcher.LauncherHelper.checkAndLoadMain(Unknown Source)

These are my classes:

• Conta.java :

public class Conta {

    static int contador;

    Conta() {
        Conta.contador ++;
    }

}

• TestaContador.java:

public class TestaContador {

    public static void main(String[] args) {
        System.out.println (" Contador : " + Conta.contador);     

        System.out.println (" Contador : " + Conta.contador);

        System.out.println (" Contador : " + Conta.contador);
    }

}