Java how can I with reflection check if a field is initialized or is default value?

Question

So, should be straight forward question.

Lets say I have a class with a lot of fields like:

String thizz;
long that;
boolean bar;

How can I, with reflection, see if the fields thizz, that and bar have been initialized or left to their default values of null, 0 and false?

Answer 1

You have only 7 primitive types and one reference type to check. If you group all Number types together, you only have four values to check for.

Object o =
for (Field field : o.getClass().getDeclaredFields()) {
 Class t = field.getType();
 Object v = field.get(o);
 if(t == boolean.class && Boolean.FALSE.equals(v)) 
   // found default value
 else if(t == char.class && ((Character) v).charValue() == 0)
   // found default value
 else if(t.isPrimitive() && ((Number) v).doubleValue() == 0)
   // found default value
 else if(v == null)
   // found default value
}  

Answer 2

Peter Lawrey's answer works fine for me, except for fields of primitive data type char, which raises the following exception in my code :

java.lang.ClassCastException: java.lang.Character cannot be cast to java.lang.Number

So I added the char case :

Object o =
for (Field field : o.getClass().getDeclaredFields()) {
 Class t = field.getType();
 Object v = field.get(o);
 if (boolean.class.equals(t) && Boolean.FALSE.equals(v)) 
   // found default value
 else if (char.class.equals(t) && ((Character) v) != Character.MIN_VALUE)
   // found default value
 else if (t.isPrimitive() && ((Number) v).doubleValue() == 0)
   // found default value
 else if(!t.isPrimitive() && v == null)
   // found default value
}  

Character.MIN_VALUE is '\u0000', which is the default value of char according to the Java Documentation on primitive data types.