### Question:
NumberAdapter extends XmlAdapter<String, Number> { @Override public String marshal(Number value){ if(value == null){ return null; } return NumberUtil.printNumber(value); }  @Override Number unmarshal(String value); @Override String marshal(Number value); static boolean isValid(Number value);  }### Answer:
@Test public void marshal(){ NumberAdapter adapter = new NumberAdapter(); assertEquals("1", adapter.marshal(1)); assertEquals("1.0", adapter.marshal(1d)); }