Does the Java ClassLoader load inner classes?

Question

If I have a inner class declaration such as:

Class A {
    public static class B {
    }
}

followed by:

Class impl         


        

Answer 1

The code below is runnable and can illustrate some of the other answers:

public class Outer
{

   private static final String TEST01 = "I'm TEST01";

   static
   {
        System.out.println("1 - Initializing class Outer, where TEST01 = " + TEST01);
   }

   public static void main(String[] args)
   {
       System.out.println("2 - TEST01       --> " + TEST01 );
       System.out.println("3 - Inner.class  --> " + Inner.class);
       System.out.println("5 - Inner.info() --> " + Inner.info() );
   }

   private static class Inner
   {

       static
       {
          System.out.println("4 - Initializing class Inner");
       }

       public static String info()
       {
           return "I'm a method in Inner";
       }
    }
}

Please, pay attention to the sequence numbers, especially in this line:

System.out.println("5 - Inner.info() --> " + Inner.info() );

When you run the program you will see the following result on the console:

1 - Initializing class Outer, where TEST01 = I'm TEST01
2 - TEST01       --> I'm TEST01
3 - Inner.class  --> class com.javasd.designpatterns.tests.Outer$Inner
4 - Initializing class Inner
5 - Inner.info() --> I'm a method in Inner

A little more detail for each step:

1 - 'Outer' is initialized when you Run the program. The static variable TEST01 is initalized before static block. Inner is not initialized.

2 - The 'main' method is called and shows the value of 'TEST01'; then,

3 - The System.out shows reference to 'Inner'. Inner is not initialized, but it was loaded (that's why it has reference in the memory model).

4 - Here's the most interesting part. Because the System.out needs to access the 'info()' method in 'Inner' ( Inner.info() ), the 'Inner' class should be initialized before returning the result of the 'info()' method. That's why this is the step 4.

5 - Finally, the System.out has all data it needs to show, and then the last line is showed on the console.

So, as it was well pointed by @sotirios-delimanolis ( Does the Java ClassLoader load inner classes? ) loading a class is different from initializing it.