import javax.annotation.CheckForNull;

/**
 * {@link Table} implementation backed by a map that associates row keys with column key / value
 * secondary maps. This class provides rapid access to records by the row key alone or by both keys,
 * but not by just the column key.
 *
 * <p>The views returned by {@link #column}, {@link #columnKeySet()}, and {@link #columnMap()} have