final List<Object> invalidated = Lists.newArrayList();
    Cache<Integer, Integer> cache =
        new AbstractCache<Integer, Integer>() {
          @Override
          public Integer getIfPresent(Object key) {
            throw new UnsupportedOperationException();
          }

          @Override
          public void invalidate(Object key) {
            invalidated.add(key);
          }
        };

    final List<Object> invalidated = Lists.newArrayList();
    Cache<Integer, Integer> cache =
        new AbstractCache<Integer, Integer>() {
          @Override
          public Integer getIfPresent(Object key) {
            throw new UnsupportedOperationException();
          }

          @Override
          public void invalidate(Object key) {
            invalidated.add(key);
          }
        };