Shows part of the code for a Matrix Multiply class that multiplies one N×N matrix (matrix A) by another (matrix B). For simplicity, it creates one mapper task for each entry of matrix A. The two...

Shows part of the code for a Matrix Multiply class that multiplies one N×N matrix (matrix A) by another (matrix B). For simplicity, it creates one mapper task for each entry of matrix A. The two matrices are stored in static matrix A and matrix B fields of the Matrix Multiply class (lines3–4). Because Java does not permit arrays to be stored directly in maps or lists, the Mapper and Reducer classes, as static inner classes of Matrix Vector, access the matrix A and matrix B fields directly. A matrix position is identified by a Row Column object that holds a row and column number (line5). (As a technical aside, Row Column objects can be used as keys in maps because they pro-vide ane quals ()operation that compares row and column numbers.) Each mapper.