10.1.1 Class modifiers
A class-declaration may optionally include a sequence of class modifiers:
It is a compile-time error for the same modifier to appear multiple times in a class declaration.
new modifier is permitted on nested classes. It specifies that the class hides an inherited member by the same name, as described in Section 10.2.2. It is a compile-time error for the
new modifier to appear on a class declaration that is not a nested class declaration.
private modifiers control the accessibility of the class. Depending on the context in which the class declaration occurs, some of these modifiers may not be permitted (Section 3.5.1).
sealed modifiers are discussed in the following sections.