Pfthb

How to fix my code below?

package mypackage;

import java.lang.reflect.Constructor;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashSet;
import java.util.List;

public class testReflection 
 public class You 
 public You(String s) 
 

 public void f(String s, int i) 
 System.out.println(i + 100);
 
 

 public static void main(String args) throws NoSuchMethodException 
 Constructor constructor =
 You.class.getConstructor(testReflection.class, String.class);
 try 
 You y = (You)constructor.newInstance("xzy");//Exception!!!!
 System.out.println("ok");
 y.f("xyz",2);
 catch(Exception e)
 e.printStackTrace();
 
 

The exception message is:

java.lang.IllegalArgumentException: wrong number of arguments
 at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
 at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
 at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
 at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
 at mypackage.testReflection.main

The hint is on this line (the constructor takes 2 parameters):

Constructor constructor =
 You.class.getConstructor(testReflection.class, String.class);

You need to send an instance of testReflection to newInstance():

testReflection outerObject = new testReflection();
You y = (You)constructor.newInstance(outerObject, "xzy");

From the documentation of Constructor#newInstance:

If the constructor's declaring class is an inner class in a non-static context, the first argument to the constructor needs to be the enclosing instance; see section 15.9.3 of The Java™ Language Specification.

Because You is an inner class, you need an instance of its enclosing class, testReflection, to create an instance of You. To do this, you can use the following:

You y = (You) constructor.newInstance(new testReflection(), "xzy");

I also recommend changing your class name to TestReflection as that follows the proper naming conventions.