完整代碼

import java.lang.annotation.*; import java.lang.reflect.Method;@Target(ElementType.METHOD) @Retention(RetentionPolicy.RUNTIME) @Documented @interface DebugTime{boolean value() default true;long timeout() default 100;String msg();int[] other() default {}; }class FibTestClass {@DebugTime(timeout=10, msg="Time Out Of Range!", other={1, 2, 3})public long fib(int n) {return (n == 0 || n==1) ? 1 : (fib(n-1)+fib(n-2));} }public class DebugAnnotationTest {public static void main(String[] args) throws NoSuchMethodException {FibTestClass obj = new FibTestClass();Class<?> clazz = obj.getClass();// show all annotationsfor(Method method : clazz.getDeclaredMethods()){System.out.println(method);for(Annotation annotation : method.getAnnotations()){System.out.println(annotation.annotationType().getName());}}Method method = clazz.getMethod("fib", int.class);System.out.println(method);if( method.isAnnotationPresent(DebugTime.class)){DebugTime debug = method.getAnnotation(DebugTime.class);// get properties of the annotationboolean requireDebug = debug.value();long timeout = debug.timeout();if(requireDebug){long time1 = System.currentTimeMillis();double fib = obj.fib(40);long time2 = System.currentTimeMillis();long time = time2-time1;System.out.println("計算結果是：" + fib);System.out.println("time used: "+time);if(time > timeout){System.err.println(debug.msg());}}}} }

測試結果

public long FibTestClass.fib(int) main.DebugTime public long FibTestClass.fib(int) 計算結果是：1.65580141E8 time used: 687 Time Out Of Range!

總結

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