Number of rows and columns of a matrix

Using the variable length, it is possible to obtain the number of rows and of columns of a matrix. Let m be a reference to a matrix (i.e., an array of arrays). Then

• m.length denotes the number of rows of the matrix m
• m[i].length denotes the number of columns of row i of matrix m

  Note: If all rows have the same number of columns (as in the previous example), we can simply use m[0].length.

Example:

double[][] v;
v = new double[15][20];
System.out.println(v.length);    // prints out 15
System.out.println(v[0].length); // prints out 20