It seems that the java-task doesn't initialize the class the same way as the 
java tool.

Here is a use case:
u.A and t.B are two classes. 
main is defined only in A.
java t.B should call t.B class initialisation
but when used inside a ant buildfile it doesn't work this way :
---------------------------------------------------------------
U:\test>ant
Buildfile: build.xml

compile:

run:
A CLASS INITIALIZATION<<<<<< hey what about B!
MAIN
I am a A.

all:

BUILD SUCCESSFUL

Total time: 1 second

U:\test>java -classpath build t.B
A CLASS INITIALIZATION
B CLASS INITIALIZATION<<<< Ok that is better!
MAIN
I am a B.

Here is a list of files and contents :

build.xml
-------------------------------
<?xml version="1.0" encoding="ISO-8859-1"?>

<project name="test" default="all">
<target name="all" depends="run" />

<target name="run" depends="compile">
  <java className="t.B">
    <classpath>
      <pathelement path="build"/>
    </classpath> 
  </java>
</target>

<target name="compile">
  <javac destdir="build" srcdir=".">
    <patternset>
      <include name="**/*.java"/>
    </patternset>
    <classpath>
      <pathelement path="."/>
    </classpath>
  </javac>
</target>
<target name="init">
  <mkdir dir="build"/>
</target>
</project>
------------------------------
t/B.java:
------------------------------
package t;
public class B extends u.A
{
  static 
  {
    System.out.println("B CLASS INITIALIZATION");
    setA(new B());
  }
  public String toString()
  { 
    return "I am a B.";
  }
}
------------------------------
u/A.java:
------------------------------
package u;
public class A
{
  public static void main(String [] args){
    System.out.println("MAIN");
    System.out.println(a);
  }
  static A a=new A();
  
  static 
  {
    System.out.println("A CLASS INITIALIZATION");
  }
  
  protected static void setA(A oa)
  {
    a=oa;
  }
   
  public String toString()
  { 
    return "I am a A.";
  }
       
}

Any clue of what is wrong?