StackOverflow2013

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POStrange Java Class-Path/Class-Loader behaviour
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copied!<p>I have a very strange Java class path behaviour when loading a class file which references other classes which are not available at runtime.</p> <p>Loading a class which has a (at runtime untouched method) which calls a constructor of another class with a parameter that is casted to a class which inherits the class of the parameter causes a class not found exception of the paramter class if only the class to load but no other classes referenced in methods of that class is in class path.</p> <p>I am using following java:</p> <pre><code>java version "1.6.0_18" Java(TM) SE Runtime Environment (build 1.6.0_18-b07) Java HotSpot(TM) 64-Bit Server VM (build 16.0-b13, mixed mode) (Windows Server 2008 R2) </code></pre> <p>Here is a sample:</p> <pre><code>public class A { public static void main(String[] args) { System.out.println("it works"); } public void foo() { new B((D)null); } } public class B { public B(C c) { } } public class C { } public class D extends C { } </code></pre> <p>Now i compile the classes, and if i execute the class A with all class files in the class path, it yields "it works".</p> <p>If i remove all classes excepet class A from the class path, following error occurs:</p> <pre><code>Exception in thread "main" java.lang.NoClassDefFoundError: C Caused by: java.lang.ClassNotFoundException: C at java.net.URLClassLoader$1.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(Unknown Source) at java.lang.ClassLoader.loadClass(Unknown Source) at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source) at java.lang.ClassLoader.loadClass(Unknown Source) Could not find the main class: A. Program will exit. </code></pre> <p>although class C should never be needed at runtime.</p> <p>Following constellation works (replaced "new B((D)null)" in class A):</p> <pre><code>public class A { public static void main(String[] args) { System.out.println("it works"); } public void foo() { D d = (D)null; d.toString(); B b = (B)null; b.toString(); new B(null); } } public class B { public B(C c) { } } public class C { } public class D extends C { } </code></pre> <p>Following constellation also works (cast to C instead of D; C does not inherit any class)</p> <pre><code>public class A { public static void main(String[] args) { System.out.println("it works"); } public void foo() { new B((C)null); } } public class B { public B(C c) { } } public class C { } public class D extends C { } </code></pre> <p>Is this an expected behaviour or a Java bug?</p>

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