[英]IllegalArgumentException: wrong number of arguments in Java Constructor.newInstance()
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?它出什么问题了? I get the following Exception: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)
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.您的String[]
被隐式转换为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。 Try this:尝试这个:
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:(
You could use dp4j verbose 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());
}
}
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