[英]instanceof Class<?> parameter
我正在嘗試編寫一個方法來返回與它獲取的類匹配的所有對象作為參數:
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;
}
}
但是,我收到一個錯誤: “ - 不兼容的操作數類型boolean和Class <capture#1-of?extends Scenario>”
“演員”由我的精靈擴展,例如Bird,Hero等。例如,想法是在給定時間獲得場景中所有鳥類的列表以進行一些計算。
知道這里發生了什么嗎? 如何測試給定對象是否是給定類的實例?
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)));
}
}
輸出:
[I'm a frog]
編輯:使用List的更優雅的getActors()版本:
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]);
}
試試這個:
cls.isInstance(yourObject)
而不是使用instanceof
運算符,只有在編譯時知道類才能使用它。
instanceof
只能與類文字一起使用。 你需要使用Class.isInstance()
,即
if (cls.isInstance(actors[k]))
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