class PaxosInstanceStore {

    public PaxosInstance getPaxosInstance( InstanceId instanceId )
    {
        if ( instanceId == null )
        {
            throw new NullPointerException( "InstanceId may not be null" );
        }

        return instances.computeIfAbsent( instanceId, i -> new PaxosInstance( this, i ) );
    }

    public  PaxosInstanceStore();
    public  PaxosInstanceStore( int maxInstancesToStore );

}