问J2EE反射类

EN

//main class:
try {
   Class<?> claz = Class.forName(claz_str);
   Parent p = (Parent) claz.getDeclaredConstructor(String.class, String[].class, String[].class).newInstance(elmName, nodes_arr, params_arr);
   } catch (Exception e) {
   throw new Exception(e.getCause());
}

// Child.class
import org.apache.commons.lang3.ArrayUtils;
public class Child extends Parent{
   public Child(){
      if(!ArrayUtils.contains(NUM_OF_PARAMS, 2)){ // <<====== run time error
        System.out.println("stuff")
      }
   }
}