public boolean init(final Configuration conf, final Configuration oldConf) {
        this.peers.clear();
        this.oldPeers.clear();
        this.quorum = this.oldQuorum = 0;
        int index = 0;
        if (conf != null) {
            for (final PeerId peer : conf) {
                this.peers.add(new UnfoundPeerId(peer, index++, false));
            }
        }

        this.quorum = this.peers.size() / 2 + 1;
        if (oldConf == null) {
            return true;
        }
        index = 0;
        for (final PeerId peer : oldConf) {
            this.oldPeers.add(new UnfoundPeerId(peer, index++, false));
        }

        this.oldQuorum = this.oldPeers.size() / 2 + 1;
        return true;
    }
Init the ballot with current conf and old conf.

@param conf    current configuration
@param oldConf old configuration
@return true if init success
jraft-core/src/main/java/com/alipay/sofa/jraft/entity/Ballot.java