1. Multi-Dimensional Arrays in Java "If debugging is the process of removing software bugs, then programming must be the process of putting them in." -- Edsger Dijkstra Plan for today: • * multi-dimensional arrays (mostly 2D) • * array creation and traversal • * accessing rows and columns in a 2D array

2. Array Creation When we create an array in Java, the number of pairs of square brackets indicates the dimensions of the array. So far, we’ve only used one-dimensional arrays: • int[] arr = new int[10]; • 2D array of integers: • int[][] matrix = new int[4][3]; • // 4 rows, 3 columns • 3D array of integers: • int[][][] arr2 = new int[3][5][2];

3. 2D Arrays • int[][] matrix = new int[4][3]; • Making sense of it all: • matrix is a reference to the entire array • matrix[i][j] is for the entry in row i, column j • indexing for both rows and columns starts at 0 • matrix[0][0] is the int in the first row and first column • matrix[i] refers to row i • matrix[0] refers to the first row, or the row with index 0 • No way of referencing a column

4. 2D Arrays • int[][] matrix = new int[3][2]; • Reasonable way to visualize 2-dimensional array • Remember: array entries are automatically initialized • arrays of numbers: entries initialized to 0 0 1 column matrix 0 1 2 row

5. 2D Array Examples • Write a method that takes a 2D array of ints, and prints the array’s elements in row order - that is, first print the elements in row 0, then row 1, then row 2, etc. • Write a method that takes a 2D array of doubles, and returns the maximum value in the array.