public boolean cancel(boolean force) throws UnexecutedInvokeException {
  if (future == null) {
    throw new UnexecutedInvokeException(this);
  }
  return cancel(false);
}

public boolean cancel ( boolean force ) throws UnexecutedInvokeException { if ( future == null ) { throw new UnexecutedInvokeException ( this ) ; } return cancel ( false ) ; }
can not cancel an invocation while it is running so if the invocation has been started you must wait for it complete by itself , but it can cancel an invocation which has not been started , thus argument force will be ignored by just use as false
