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

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.)

Solution 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"

Solution 2:

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