Java 类的实例<&燃气轮机;参数
我正在尝试编写一个方法,以返回与它作为参数获取的类匹配的所有对象:Java 类的实例<&燃气轮机;参数,java,instanceof,Java,Instanceof,我正在尝试编写一个方法,以返回与它作为参数获取的类匹配的所有对象: public class Scenario extends View { ... private Actor[] actors = new Actor[1024]; ... public Actor[] getActors(Class<?> cls) { //Count actors corresponding to class cls int
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;
}
}
公共类场景扩展视图{
...
私有参与者[]参与者=新参与者[1024];
...
公共参与者[]获取参与者(类别cls){
//计算与类cls相对应的参与者
int-cnt=0;
对于(int i=0;i请尝试以下方法:
cls.isInstance(yourObject)
而不是使用instanceof
运算符,该运算符只能在编译时知道类时使用。instanceof
只能与类文本一起使用。您需要使用
编辑:更优雅的getActors()版本,使用列表:
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]);
}
publicstaticactor[]getActors(类cls){
LinkedList chosenActors=新LinkedList();
for(Actor-Actor:actors)if(cls.isInstance(Actor))chosenActors.add(Actor);
返回chosenActors.toArray(新Actor[0]);
}
非常感谢!您知道使用isInstance方法对性能的影响吗?很可能不会比instanceof
慢。非常感谢您花时间编写一个示例。不客气!如果您在生产代码中使用此示例,我会考虑使用列表作为返回类型或临时变量,因为它很容易在循环索引中出错。正如您所说,使用集合确实看起来更优雅,实际上整个场景机制以前都使用集合。我把它弄得很难看,因为集合分配东西(迭代器)我需要这个用于渲染循环的actor数组。我现在已经完成了它的实现,并且我摆脱了大量的GC_for_MALLOC事件。这很遗憾,因为使用ArrayLists时代码看起来很棒…(我以前没有提到过,但这是一个android应用程序,所以针对低规格设备)
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)));
}
}
[I'm a frog]
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]);
}