I'm trying to determine the type of a field on an object. I don't know the type of the object when it is passed to me but I need to find fields which are long
s. It is easy enough to distinguish the boxed Long
s but the primitive long
seems more difficult.
I can make sure that the objects passed to me only have Longs
, not the primitives, but I'd rather not. So what I have is:
for (Field f : o.getClass().getDeclaredFields()) {
Class<?> clazz = f.getType();
if (clazz.equals(Long.class)) {
// found one -- I don't get here for primitive longs
}
}
A hacky way, which seems to work, is this:
for (Field f : o.getClass().getDeclaredFields()) {
Class<?> clazz = f.getType();
if (clazz.equals(Long.class) || clazz.getName().equals("long")) {
// found one
}
}
I'd really like a cleaner way to do this if there is one. If there is no better way then I think that requiring the objects I receive to only use Long
(not long
) would be a better API.
Any ideas?
The java. lang. Class. isPrimitive() method can determine if the specified object represents a primitive type.
Primitive types are the most basic data types available within the Java language. There are 8: boolean , byte , char , short , int , long , float and double . These types serve as the building blocks of data manipulation in Java. Such types serve only one purpose — containing pure, simple values of a kind.
Primitive data types - includes byte , short , int , long , float , double , boolean and char.
You're using the wrong constant to check for Long primitives - use Long.TYPE
, each other primitive type can be found with a similarly named constant on the wrapper. eg: Byte.TYPE
, Character.TYPE
, etc.
o.getClass().getField("fieldName").getType().isPrimitive();
You can just use
boolean.class
byte.class
char.class
short.class
int.class
long.class
float.class
double.class
void.class
If you are using reflection, why do you care, why do this check at all. The get/set methods always use objects so you don't need to know if the field is a primitive type (unless you try to set a primitive type to the null value.)
In fact, for the method get() you don't need to know which type it is. You can do
// any number type is fine.
Number n = field.get(object);
long l = n.longValue();
If you are not sure if it is a Number type you can do
Object o = field.get(object); // will always be an Object or null.
if (o instanceof Number) {
Number n = (Number) o;
long l = n.longValue();
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