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javaclassloader

Why does the simple code load many classes?

This is a very simple code:

package test;
public class Test {
    public static void main(String[] args) {
        System.out.println("test");
    }
}

I run it: java -verbose:class Test, and following is the output. Why are so many classes loaded? Isn't Java load class as needed?

[Opened C:\Program Files\Java\jdk1.7.0_11\jre\lib\rt.jar]
[Loaded java.lang.Object from C:\Program Files\Java\jdk1.7.0_11\jre\lib\rt.jar]
[Loaded java.io.Serializable from C:\Program Files\Java\jdk1.7.0_11\jre\lib\rt.jar]
[Loaded java.lang.Comparable from C:\Program Files\Java\jdk1.7.0_11\jre\lib\rt.jar]
[Loaded java.lang.CharSequence from C:\Program Files\Java\jdk1.7.0_11\jre\lib\rt.jar]
[Loaded java.lang.String from C:\Program Files\Java\jdk1.7.0_11\jre\lib\rt.jar]
[Loaded java.lang.reflect.GenericDeclaration from C:\Program        Files\Java\jdk1.7.0_11\jre\lib\rt.jar]
[Loaded java.lang.reflect.Type from C:\Program Files\Java\jdk1.7.0_11\jre\lib\rt.jar]
[Loaded java.lang.reflect.AnnotatedElement from C:\Program Files\Java\jdk1.7.0_11\jre\lib\rt.jar]
[Loaded java.lang.Class from C:\Program Files\Java\jdk1.7.0_11\jre\lib\rt.jar]
[Loaded java.lang.Cloneable from C:\Program Files\Java\jdk1.7.0_11\jre\lib\rt.jar]
[Loaded java.lang.ClassLoader from C:\Program Files\Java\jdk1.7.0_11\jre\lib\rt.jar]
[Loaded java.lang.System from C:\Program Files\Java\jdk1.7.0_11\jre\lib\rt.jar]
[Loaded java.lang.Throwable from C:\Program Files\Java\jdk1.7.0_11\jre\lib\rt.jar]
[Loaded java.lang.Error from C:\Program Files\Java\jdk1.7.0_11\jre\lib\rt.jar]
...
test
[Loaded java.lang.Shutdown from C:\Program Files\Java\jdk1.7.0_11\jre\lib\rt.jar]
[Loaded java.lang.Shutdown$Lock from C:\Program Files\Java\jdk1.7.0_11\jre\lib\rt.jar]
Solution

  • Classes can themselves load classes in a transitive manner. Your program makes use of the System class, which may itself reference such system classes like java.io.Serializable.

    The classes in your listing also happen to be very frequently used classes. It may simply be that the virtual machine is loading them forcibly, in order to avoid a delayed initialization. These classes are bound to be used in any non-trivial program.