JDK版本不同步问题！

[root@AY1402191009362242d1Z ]# java HelloMain

Exception in thread "main" java.lang.UnsupportedClassVersionError: HelloMain : Unsupported major.minor version 51.0

        at java.lang.ClassLoader.defineClass1(Native Method)

        at java.lang.ClassLoader.defineClassCond(ClassLoader.java:631)

        at java.lang.ClassLoader.defineClass(ClassLoader.java:615)

        at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141)

        at java.net.URLClassLoader.defineClass(URLClassLoader.java:283)

        at java.net.URLClassLoader.access$000(URLClassLoader.java:58)

        at java.net.URLClassLoader$1.run(URLClassLoader.java:197)

        at java.security.AccessController.doPrivileged(Native Method)

        at java.net.URLClassLoader.findClass(URLClassLoader.java:190)

        at java.lang.ClassLoader.loadClass(ClassLoader.java:306)

        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)

        at java.lang.ClassLoader.loadClass(ClassLoader.java:247)

Could not find the main class: HelloMain.  Program will exit.