public PersistentPageFile(int pageSize,String fileName,Class<P> pageclass){
  super(pageSize);
  this.pageclass=pageclass;
  File f=new File(fileName);
  existed=f.exists();
  try {
    file=new RandomAccessFile(f,"rw");
  }
 catch (  IOException e) {
    throw new AbortException("IO error in loading persistent page file.",e);
  }
}

public PersistentPageFile ( int pageSize , String fileName , Class < P > pageclass ) { super ( pageSize ) ; this . pageclass = pageclass ; File f = new File ( fileName ) ; existed = f . exists ( ) ; try { file = new RandomAccessFile ( f , "rw" ) ; } catch ( IOException e ) { throw new AbortException ( "IO error in loading persistent page file." , e ) ; } }
creates a new persistentpagefile from an existing file .
