我在執行以下方法時收到空指針異常。我已調試並發現cons.getAnnotation(MyAssessment.class);
正在返回null
。普萊舍幫助在使用用戶定義的註釋時獲取java.lang.NullPointerException
import java.lang.annotation.*;
import java.lang.reflect.*;
enum GradeLevel { POOR, AVERAGE, GOOD, VERYGOOD, EXTRAORDINARY }
@interface MyAssessment {
GradeLevel score();
}
public class Problem {
@MyAssessment(score=GradeLevel.GOOD)
public Problem(){
System.out.println("This is a constuructor");
}
public static void main(String... args){
try {
Class c = new Problem().getClass();
Constructor cons = c.getDeclaredConstructor();
MyAssessment an = (MyAssessment) cons.getAnnotation(MyAssessment.class);
System.out.println("YOUR SCORE IS : " + an.score());
}
catch(NoSuchMethodException nsme) {
System.out.println("Constructor thrown exception");
}
}
}