CODEWITHSUNDEEP
javaclassclassloaderloader
Ring
Ring

Reputation: 2309

Loading an array with a classloader

I'm trying to run this code:

public class ClassLoaderTest
{
  public static void main(String[] args) throws Exception
  {
    Object[] obj = new Object[]{};
    String cname = obj.getClass().getName();
    System.out.println(cname);

    ClassLoaderTest.class.getClassLoader().loadClass(cname);
  }
}

But it throws a ClassNotFoundException. Interestingly, if I instead use this line:

Class.forName(cname);

it works just fine.

Whats going on here?

edit: I'm using Java 6. The println prints this:

[Ljava.lang.Object;

Upvotes: 5

Views: 1267

Answers (3)

Andy Turner
Andy Turner

Reputation: 140554

Looking at the source code around the line that the exception is thrown on, it looks like it is trying to build the filename of the class like this:

String path = name.replace('.', '/').concat(".class");

Given that the value of cname is [Ljava.lang.Object;, I am not especially surprised that the .class file can't be found.

Upvotes: 1

Elliott Frisch
Elliott Frisch

Reputation: 201537

First, using a class loader to try and load java.lang.Object array is unlikely to work (since java.lang.Object is loaded by the default class loader). Next, the name given by 

Object[] obj = new Object[]{};
String cname = obj.getClass().getName();
System.out.println(cname);

is [Ljava.lang.Object;. Clearly that isn't a class that can be resolved by a ClassLoader - the javadoc says (in part) A class loader is an object that is responsible for loading classes; note it does not say it's responsible for loading arrays. In reflection arrays are handled with java.lang.reflect.Array which says, in part, The Array class provides static methods to dynamically create and access Java arrays. which seems to be what you're looking for.

Upvotes: 1

Jean-François Savard
Jean-François Savard

Reputation: 21004

They are not the same at all,

Class.forName return the Class object associated with the class of the given name.

In your example, you give to loadClass a String that represent the name of a class, instead of giving it directly a class.

This method does allow you to give a name, however it must be the binary name of the class, not just the class name.

Any class name provided as a String parameter to methods in ClassLoader must be a binary name as defined by The Java™ Language Specification.

Upvotes: 3

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