private void checkPredecessor() {
        try {
            if (predecessor != null && !predecessor.isActive()) {
                System.out.println("Predecessor of node " + chordId.toDecString() + " fails.");
                predecessor = null;
            }
        } catch (RemoteException e) {
            System.out.println("Predecessor of node " + chordId.toDecString() + " fails.");
            predecessor = null;
        }
    }