code: public void associateSuperDef(ZooClassDef superDef) {
  		if (this.superDef != null) {
  			throw new IllegalStateException();
  		}
  
  		if (superDef == null) {
  			throw new IllegalArgumentException();
  		}
  		
  		//class invariant
  		if (superDef.getOid() != oidSuper) {
  			throw new IllegalStateException("s-oid= " + oidSuper + " / " + superDef.getOid() + 
  					"  class=" + className);
  		}
  		
  		this.superDef = superDef;
  	}
docs: Only to be used during database startup to load the schema-tree.
  @param superDef The super class