P4
In `src/hotspot/share/gc/shared/space.hpp`:
```
class FilteringDCTOC : public DirtyCardToOopClosure {
class ContiguousSpaceDCTOC : public FilteringDCTOC {
```
`FilteringDCTOC` has only a single subclass. One can merge super/sub class and some virtual methods would become non-virtual.
```
class FilteringDCTOC : public DirtyCardToOopClosure {
class ContiguousSpaceDCTOC : public FilteringDCTOC {
```
`FilteringDCTOC` has only a single subclass. One can merge super/sub class and some virtual methods would become non-virtual.
