### Question:
LongWrapper extends AbstractWrapper<Long> implements NumberWrapper<Long> { @Override public void decrement() { Long value = doGet(); if (value != null) { doSet(value - 1L); } } LongWrapper();  LongWrapper(Long value); @Override void set(Number v); @Override void increment(); @Override void decrement(); @Override R accept(WrapperVisitor<R, P, Q, TH> visitor, P p, Q q);  }### Answer:
@Test public void testDecrement() { LongWrapper wrapper = new LongWrapper(10L); wrapper.decrement(); assertEquals(new Long(9L), wrapper.get()); }