IllegalArgumentException：Java Constructor.newInstance() 中的参数数量错误
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IllegalArgumentException: wrong number of arguments in Java Constructor.newInstance()
提问by xandy
Consider the following code,
考虑以下代码，
public class StartUp {
public StartUp(String[] test){}
public static void main(String[] args) throws Exception{
Constructor cd = StartUp.class.getConstructor(String[].class);
System.out.println(cd.newInstance(new String[]{}).toString());
}
}
What's wrong with it? I get the following Exception:
它出什么问题了？我收到以下异常：
Exception in thread "main" java.lang.IllegalArgumentException: wrong number of arguments at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27) at java.lang.reflect.Constructor.newInstance(Constructor.java:513) at com.test.StartUp.main(StartUp.java:10)
线程“main”中的异常 java.lang.IllegalArgumentException: sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance0(Native Method) 处的参数数量错误newInstance(DelegatingConstructorAccessorImpl.java:27) at java.lang.reflect.Constructor.newInstance(Constructor.java:513) at com.test.StartUp.main(StartUp.java:10)
回答by Jon Skeet
Your String[]is being implicitly converted to Object[]and taken as an empty array of arguments, instead of as a single argument which is an empty array. Try this:
您String[]正在被隐式转换Object[]并作为一个空的参数数组，而不是作为一个空数组的单个参数。试试这个：
Object arg = new String[0];
System.out.println(cd.newInstance(arg).toString());
or
或者
System.out.println(cd.newInstance(((Object)new String[0]).toString());
or even avoid the compiler having to create the array for you at all:
甚至完全避免编译器必须为您创建数组：
System.out.println(cd.newInstance(new Object[] { new String[0] }).toString());
Basically this is a mixture of varargs handling and array covariance :(
基本上这是可变参数处理和数组协方差的混合:(
回答by simpatico
You could use dp4jverbose option to answer your question, and get the correct reflection code that you need:
您可以使用dp4j详细选项来回答您的问题，并获得您需要的正确反射代码：
$ vim ReflectedAcces.java
class StartUp {
private StartUp(String[] test){}
}
public class ReflectedAcces{
@com.dp4j.InjectReflection
public static void main(String[] args) throws Exception{
StartUp su = new StartUp(new String[]{});
System.out.println(su.toString());
}
}
$ javac -cp dp4j-1.0-jar-with-dependencies.jar -Averbose=true ReflectedAcces.java
...
ReflectedAcces.java:10: Note:
class StartUp {
private StartUp(String[] test) {
}
}
public class ReflectedAcces {
public ReflectedAcces() {
super();
}
@com.dp4j.InjectReflection()
public static void main(String[] args) java.lang.ClassNotFoundException, java.lang.NoSuchFieldException, java.lang.IllegalAccessException, java.lang.NoSuchMethodException, java.lang.reflect.InvocationTargetException, java.lang.InstantiationException {
final java.lang.reflect.Constructor startUpConstructor = Class.forName("StartUp").getDeclaredConstructor(.java.lang.String[].class);
startUpConstructor.setAccessible(true);
StartUp su = (.StartUp)startUpConstructor.newInstance(new .java.lang.Object[1][]{new String[]{}});
System.out.println(su.toString());
}
}
