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
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]);
}