Java reflection: how to get field value from an object, not knowing its class

Question

Say, I have a method that returns a custom List with some objects. They are returned as Object to me. I need to get value of a certain field from these objects, but I don't know the objects' class.

Is there a way to do this via Reflecion or somehow else?

Answer 1

Assuming a simple case, where your field is public:

List list; // from your method for(Object x : list) {     Class<?> clazz = x.getClass();     Field field = clazz.getField("fieldName"); //Note, this can throw an exception if the field doesn't exist.     Object fieldValue = field.get(x); } 

But this is pretty ugly, and I left out all of the try-catches, and makes a number of assumptions (public field, reflection available, nice security manager).

If you can change your method to return a List<Foo>, this becomes very easy because the iterator then can give you type information:

List<Foo> list; //From your method for(Foo foo:list) {     Object fieldValue = foo.fieldName; } 

Or if you're consuming a Java 1.4 interface where generics aren't available, but you know the type of the objects that should be in the list...

List list; for(Object x: list) {    if( x instanceof Foo) {       Object fieldValue = ((Foo)x).fieldName;    } } 

No reflection needed :)