In Java, is it possible to know whether a class has already been loaded?

Question

Is it possible to know whether a Java class has been loaded, without attempting to load it? Class.forName attempts to load the class, but I don't want this side effect. Is there another way?

(I don't want to override the class loader. I'm looking for a relatively simple method.)

Answer 1

(Thanks to Aleksi) This code:

public class TestLoaded {      public static void main(String[] args) throws Exception {           java.lang.reflect.Method m = ClassLoader.class.getDeclaredMethod("findLoadedClass", new Class[] { String.class });           m.setAccessible(true);           ClassLoader cl = ClassLoader.getSystemClassLoader();           Object test1 = m.invoke(cl, "TestLoaded$ClassToTest");           System.out.println(test1 != null);           ClassToTest.reportLoaded();           Object test2 = m.invoke(cl, "TestLoaded$ClassToTest");           System.out.println(test2 != null);      }      static class ClassToTest {           static {                System.out.println("Loading " + ClassToTest.class.getName());           }           static void reportLoaded() {                System.out.println("Loaded");           }      } } 

Produces:

false Loading TestLoaded$ClassToTest Loaded true 

Note that the example classes are not in a package. The full binary name is required.

An example of a binary name is "java.security.KeyStore$Builder$FileBuilder$1"

Answer 2

You can use the findLoadedClass(String) method in ClassLoader. It returns null if the class is not loaded.