### Question:
PrimitiveDoubleWrapper extends DoubleWrapper { @Override public void set(Number v) { set(v == null ? defaultValue : v.doubleValue()); } PrimitiveDoubleWrapper();  PrimitiveDoubleWrapper(double value); @Override void set(Number v); @Override Double getDefault(); @Override boolean isPrimitiveWrapper(); @Override R accept(WrapperVisitor<R, P, Q, TH> visitor, P p, Q q);  }### Answer:
@Test void set() { PrimitiveDoubleWrapper wrapper = new PrimitiveDoubleWrapper(); wrapper.set(10); assertEquals(10d, wrapper.get()); wrapper.set(new BigDecimal(20)); assertEquals(20d, wrapper.get()); }
@Test void set_null() { PrimitiveDoubleWrapper wrapper = new PrimitiveDoubleWrapper(); wrapper.set(null); assertEquals(0d, wrapper.get()); wrapper.set((Number) null); assertEquals(0d, wrapper.get()); }