Class PairLexicoder<A extends Comparable<A>,​B extends Comparable<B>>

  • All Implemented Interfaces:
    Encoder<ComparablePair<A,​B>>, Lexicoder<ComparablePair<A,​B>>

    public class PairLexicoder<A extends Comparable<A>,​B extends Comparable<B>>
    extends AbstractLexicoder<ComparablePair<A,​B>>
    This class is a lexicoder that sorts a ComparablePair. Each item in the pair is encoded with the given lexicoder and concatenated together. This makes it easy to construct a sortable key based on two components. There are many examples of this- but a key/value relationship is a great one. If we decided we wanted a two-component key where the first component is a string and the second component a date which is reverse sorted, we can do so with the following example:
     StringLexicoder strEncoder = new StringLexicoder();
     ReverseLexicoder<Date> dateEnc = new ReverseLexicoder<>(new DateLexicoder());
     PairLexicoder<String,Date> pair = new PairLexicoder<>(strEncoder, dateEnc);
     long now = System.currentTimeMillis();
     byte[] pair1 = pair.encode(new ComparablePair<>("com", new Date(now)));
     byte[] pair2 = pair.encode(new ComparablePair<>("com", new Date(now + 500)));
     byte[] pair3 = pair.encode(new ComparablePair<>("org", new Date(now + 1000)));
    In the example, pair2 will be sorted before pair1. pair3 will occur last since 'org' is sorted after 'com'. If we just used a DateLexicoder instead of a ReverseLexicoder, pair1 would have been sorted before pair2.