Question

I have something like:

Field [] fields = claz.getDeclaredFields();
 for(Field f : fields){
    f.setAccessible(true);
    if(f.getType().equals(List.class)){
        Method m = f.getType().getMethod("size");
        int length = (Integer)m.invoke(f.get(node));
        System.out.println("length "+ length);
        }
}

it does work, but I’m wondering to know if there is any other good approaches, like something that will work for all other collections (TreeSet, HashSet, etc…), or the only way is that, I have to check for each type like what I already have?

thanks

Answer 1

In a Field object you could retrieve the Type and pass it as parameter for the method isAssignableFrom of Collection.class.

Like:

...
boolean isCollection = Collection.class.isAssignableFrom(f.getType())
...

From documentation the method isAssignableFrom:

Determines if the class or interface represented by this Class object
is either the same as, or is a superclass or superinterface of, the
class or interface represented by the specified Class parameter. It
returns true if so; otherwise it returns false. If this Class object
represents a primitive type, this method returns true if the specified
Class parameter is exactly this Class object; otherwise it returns
false.

The same should be done with Map:

boolean isMap = Map.class.isAssignableFrom(f.getType());