1 / 9

Multi-dimensional arrays

Multi-dimensional arrays. Allows you to work with matrices int array[][] = new int[20][30] First dimension is number of rows Second dimension is number of columns Can have more than two dimensions Allocated row-pointer in memory A row can be stored anywhere in memory

Faraday
Download Presentation

Multi-dimensional arrays

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Multi-dimensional arrays • Allows you to work with matrices int array[][] = new int[20][30] • First dimension is number of rows • Second dimension is number of columns • Can have more than two dimensions • Allocated row-pointer in memory • A row can be stored anywhere in memory • Elements in a row are stored contiguously • Can visualize as array of arrays

  2. Transpose class transpose { public static void main(String args[]) { int i, j; int table[][] = new int[3][4]; int ttable[][] = new int[4][3]; for(i=0; i < 3; ++i) { for(j=0; j < 4; ++j) { table[i][j] = (i*4)+j+1; System.out.print(table[i][j] + " "); } System.out.println(); } System.out.println(); for(j=0; j < 4; ++j) { for(i=0; i < 3; ++i) { ttable[j][i] = table[i][j]; System.out.print(ttable[j][i] + " "); } System.out.println(); } } }

  3. Matrix multiplication class MatrixMultiply { public static void main (String arg[]) { int m = 20, n = 30, p = 40; double A[][] = new double[m][n]; double B[][] = new double[n][p]; double C[][]; InitializeArray (A, m, n); InitializeArray (B, n, p); C = Multiply (A, B, m, n, p); } // continued in next slide

  4. Matrix multiplication public static void InitializeArray (double x[][], int m, int n) { int i, j; for (i=0;i<m;i++) { for (j=0;j<n;j++) { x[i][j] = i+j; } } }

  5. Matrix multiplication public static double[][] Multiply (double x[][], double y[][], int p, int q, int r) { double z[][] = new double[p][r]; int i, j, k; for (i=0;i<p;i++) { for (j=0;j<r;j++) { z[i][j] = 0; for (k=0;k<q;k++) { z[i][j] += (x[i][k]*y[k][j]); } } } return z; } } // end class

  6. Allocating a triangular matrix • May save memory for symmetric matrices • Allocate space to store the starting addresses of m rows • Then allocate the m rows themselves int m = 20; double[] triangle[] = new double[m][]; int i; for (i=0;i<m;i++) { // allocate lower triangle triangle[i] = new double[i+1]; }

  7. arraylength class arraylength { public static void main(String args[]) { int list[] = new int[10]; int nums[] = { 1, 2, 3 }; int table[][] = { // a variable-length table {1, 2, 3}, {4, 5}, {6, 7, 8, 9} };

  8. System.out.println("length of list is " + list.length); System.out.println("length of nums is " + nums.length); System.out.println("length of table is " + table.length); System.out.println("length of table[0] is " + table[0].length); System.out.println("length of table[1] is " + table[1].length); System.out.println("length of table[2] is " + table[2].length); System.out.println();

  9. // use length to initialize list for(int i=0; i < list.length; i++) list[i] = i * i; System.out.print("Here is list: "); // now use length to display list for(int i=0; i < list.length; i++) System.out.print(list[i] + " "); System.out.println(); } }

More Related