There are several methods in Scope, mainly lookup which have two versions, the main difference between both is a parameter of type Filter<Symbol>. The version without the filter parameter just call the other one:

    public Entry lookup(Name name) {
        return lookup(name, noFilter);
    }
    public Entry lookup(Name name, Filter<Symbol> sf) {
        Entry e = table[getIndex(name)];
        if (e == null || e == sentinel)
            return sentinel;
        while (e.scope != null && (e.sym.name != name || !sf.accepts(e.sym)))
            e = e.shadowed;
        return e;
    }
  
This is the definition of noFilter:

    static final Filter<Symbol> noFilter = new Filter<Symbol>() {
        public boolean accepts(Symbol s) {
            return true;
        }
    };

The problem of this code is that the method: public Entry lookup(Name name), is called so many times that paying for a call to the accepts method of noFilter implies a performance slowdown.