Taking two or more sorted streams and combining them into one. The Java class library
does not have any tools for doing this. Merging can also be done with streams that
reside on disk. You don’t need the entire set in RAM (Random Access Memory)
to merge. Large sorts take advantage of this by sorting RAM-sized clumps of data,
writing them to disk, the merging the clumps in an N-way merge, creating fewer but
longer sorted clumps.