获取 java.lang.NullPointerException 时调用 Method.invoke
2022-09-04 01:35:04
我正在学习Java注释的本教程,并实现了测试注释,如下所示。但是在运行代码时,我得到以下输出。
java.lang.NullPointerException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:616)
at TestAnnotationParser.parse(Demo.java:24)
at Demo.main(Demo.java:51)
Passed:0 Fail:1
以下是我的代码。有人能指出我做错了什么吗?
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import java.lang.reflect.Method;
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
@interface Test {
Class expected();
}
class TestAnnotationParser {
public void parse(Class<?> clazz) throws Exception {
Method[] methods = clazz.getMethods();
int pass = 0;
int fail = 0;
for (Method method : methods) {
if (method.isAnnotationPresent(Test.class)) {
Test test = method.getAnnotation(Test.class);
Class expected = test.expected();
try {
method.invoke(null);
pass++;
} catch (Exception e) {
if (Exception.class != expected) {
e.printStackTrace();
fail++;
} else {
pass++;
}
}
}
}
System.out.println("Passed:" + pass + " Fail:" + fail);
}
}
class MyTest {
@Test(expected = RuntimeException.class)
public void testBlah() {
}
}
public class Demo {
public static void main(String[] args) {
TestAnnotationParser parser = new TestAnnotationParser();
try {
parser.parse(MyTest.class);
} catch (Exception e) {
e.printStackTrace();
}
}
}