Problems with Reflection in Java

I am having trouble understanding why the following bit of code results in a NoSuchMethodException. Everyone, please

take a look at this and help me figure out the problem.

/**********************************/

import java.util.*;

import java.lang.reflect.*;


public class test

{

public static void main(String args[])

{

runTest(new HashSet());

}

static void runTest(Set set)

{

try

{

Class the_class=set.getClass();

Class[] args=new Class[] {the_class};

Constructor constructor=the_class.getConstructor(args);

}

catch (Exception e)

{

System.out.println(e);

}

}

}


/**********************************/

Hye Luke,


What's up?! :)

Well, I came across your problem and decided to give it a shot! I just gotta tell you that you were getting that error

cos' there actually is no method called "getConstructor()" as far as I know. There is a method called

"getConstructors()" which returns you an array.

Here is the edited code :


--------------------------------------

import java.util.*;

import java.lang.reflect.*;


public class test

{

public static void main(String args[])

{

runTest(new HashSet());

}

static void runTest(Set set)

{

try

{

Class the_class = set.getClass();

System.out.println("Class the_class : " + the_class);

Class[] args = new Class[] {the_class};

System.out.println("Class[] args : " + args);

Constructor[] constructor = the_class.getConstructors();

System.out.println("Constructor[] constructor : " + constructor);

}

catch (Exception e)

{

System.out.println(e);

}

}

}

________________________________________


See ya around...mail me if you hear sumthin' new related to Java....


Long Live Java....


Davender aka JaVaFLow

Thanks for the quick reply. I am not sure if I should have

been more specific, but I used the JDK1.2 to compile this little bugger of

a test. In Sun's JDK1.2 documentation, it states that there is in fact a

Constructor getConstructor(Class[] parameterTypes) method. However,

it doesn't appear to work correctly in my test application. Is this a bug, or

is it user (my own) error?


-Luke

I think the method for getting the constructor is


getConstructors();

// and not

getContructor();


See carefully .


this method returns an array which contains the various contructors used

by the given class


bye

sunil

Look in the Java API documentation everybody! It plainly says that

there is indeed a method:


Constructor getConstructor(Class[] parameterTypes)


Of course, there is also a:


Constructor[] getConstructors()



Now, is it me, or is the: "Constructor getConstructor(Class[] parameterTypes)"

that I used in the code in my original post, broken?


Here is the Java2 code to test run, showing the broken method:


/**********************************/

import java.util.*;

import java.lang.reflect.*;


public class test

{

public static void main(String args[])

{

runTest(new HashSet());

}

static void runTest(Set set)

{

try

{

Class the_class=set.getClass();

Class[] args=new Class[] {the_class};

Constructor constructor=the_class.getConstructor(args);

}

catch (Exception e)

{

System.out.println(e);

}

}

}


/**********************************/

Well, the getConstructor(Class []) takes a class array and returns a constructor. Your code pays in args to the getConstructor. I'm not sure how
args gets passed down at all (how can runTest see it), but even so I don't
think args is a Class array--it's a String array.