instanceof Class<?> parameter

Question

I'm trying to write a method to return all objects that match the class it gets as a parameter:

public class Scenario extends View {      ...      private Actor[] actors = new Actor[1024];      ...      public Actor[] getActors(Class<?> cls) {         //Count actors corresponding to class cls         int cnt = 0;               for (int i = 0; i<actorsCount; i++)            if (actors[i] instanceof cls) cnt++;            //Build a new array;         Actor[] clsActors = new Actor[cnt];          //Fill it         for (int j = 0, k=0; j<cnt; k++)            if (actors[k] instanceof cls)               clsActors[j++] = actors[k];          return clsActors;     } } 

However, I'm getting an error: "- Incompatible operand types boolean and Class＜capture#1-of ? extends Scenario＞"

'Actor' is extended by my sprites, say Bird, Hero, etc. The idea is, for example, to get a list of all Birds on the Scenario at a given time for some calculations.

Any idea what's going on here? How to test if a given object is an instance of a given class?

Answer 1

import java.util.Arrays;  public class Main {     static class Actor {}     static class Frog extends Actor {@Override public String toString() {return "I'm a frog";}}     static class Lizard extends Actor {@Override public String toString() {return "I'm a lizard";}}          private static Actor[] actors;                  public static Actor[] getActors(Class<?> cls) {             //Count actors corresponding to class cls             int cnt = 0;                   for (int i = 0; i<actors.length; i++)                if (cls.isInstance(actors[i])) cnt++;               //Build a new array;             Actor[] clsActors = new Actor[cnt];              //Fill it             for (int j = 0, k=0; j<cnt; k++)                     if (cls.isInstance(actors[k]))                   clsActors[j++] = actors[k];              return clsActors;         }      public static void main(String[] args)     {             actors = new Actor[] {new Frog(), new Lizard()};             System.out.println(Arrays.toString(getActors(Frog.class)));     } } 

Output:

[I'm a frog] 

Edit: More elegant version of getActors() using a List:

    public static Actor[] getActors(Class<?> cls) {         LinkedList<Actor> chosenActors = new LinkedList<Actor>();                    for(Actor actor: actors) if(cls.isInstance(actor)) chosenActors.add(actor);                                  return chosenActors.toArray(new Actor[0]);     } 

Answer 2

Try this:

cls.isInstance(yourObject) 

instead of using the instanceof operator, which can only be used if you know the class at compile time.