BungeeCord error

bungee@proxy:~/bungee$ java -Xmx512M -jar BungeeCord.jar
Exception in thread "main" java.lang.UnsupportedClassVersionError: net/md_5/bungee/api/ProxyServer : 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)
at...

BungeeCord error