You should always annotate methods with @Override if it's available.
In JDK 5 this means overriding methods of superclasses, in JDK 6, and 7 it means overriding methods of superclasses, and implementing methods of interfaces. The reason, as mentioned previously, is it allows the compiler to catch errors where you think you are overriding (or implementing) a method, but are actually defining a new method (different signature).
the reason it's not mandatory to annotate implementing methods of interfaces is that JDK 5 flagged this as a compile error. If JDK 6 made this annotation mandatory, it would break backwards compatibility.
I am not an Eclipse user, but in other IDEs (IntelliJ), the @Override annotation is only added when implementing interface methods if the project is set as a JDK 6+ project. I would imagine that Eclipse is similar.
如果@Override接口时Eclipse提示错误，则需要改Java编辑器的“Compiler compliance level”
