解读Javac之Types方法2

/**
     * Return the (most specific) base type of t that starts with the
     * given symbol.  If none exists, return null.
     *
     * @param t a type
     * @param sym a symbol
     */
    public Type asSuper(Type t, Symbol sym) {
        return asSuper.visit(t, sym);
    }

 private SimpleVisitor<Type,Symbol> asSuper = new SimpleVisitor<Type,Symbol>() {

            public Type visitType(Type t, Symbol sym) {
                return null;
            }

            @Override
            public Type visitClassType(ClassType t, Symbol sym) {
                if (t.tsym == sym)
                    return t;

                Type st = supertype(t);
                if (st.tag == CLASS || st.tag == TYPEVAR || st.tag == ERROR) {
                    Type x = asSuper(st, sym);
                    if (x != null)
                        return x;
                }
                if ((sym.flags() & INTERFACE) != 0) {
                    for (List<Type> l = interfaces(t); l.nonEmpty(); l = l.tail) {
                        Type x = asSuper(l.head, sym);
                        if (x != null)
                            return x;
                    }
                }
                return null;
            }

            @Override
            public Type visitArrayType(ArrayType t, Symbol sym) {
                return isSubtype(t, sym.type) ? sym.type : null;
            }

            @Override
            public Type visitTypeVar(TypeVar t, Symbol sym) {
                if (t.tsym == sym)
                    return t;
                else
                    return asSuper(t.bound, sym);
            }

            @Override
            public Type visitErrorType(ErrorType t, Symbol sym) {
                return t;
            }
};