How to find out if a field is instanceof a type via reflection?

Solution 1:

You have to use isAssignableFrom.

Solution 2:

The rather baroquely-named Class.isAssignableFrom is what you're after. I usually end up having to read the javadoc to make sure I get it the right way around:

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.

Specifically, this method tests whether the type represented by the specified Class parameter can be converted to the type represented by this Class object via an identity conversion or via a widening reference conversion.

For example:

public class X {
    
   public int i;

   public static void main(String[] args) throws Exception {
      Class<?> myType = Integer.class;
      Object o = new X();
      
      for (Field field : o.getClass().getFields()) {
         if (field.getType().isAssignableFrom(myType)) {
            System.out.println("Field " + field + " is assignable from type " + o.getClass());
         }
      }
   }
}