1. 11-1 Chapter 11 2D Arrays Asserting Java Rick Mercer

2. 11-2 Two-Dimensional Arrays  Data is sometimes conveniently viewed as tabular data ( in rows and columns) Quiz 1 2 3 4 5 6 7 8 76 82 78 85 56 72 84 92 Quiz 1 2 3 4 5 6 7 8 76 82 78 85 56 72 84 92 86 91 92 100 48 68 92 78 86 91 92 100 48 68 92 78 76 82 48 95 76 72 78 92 76 82 48 95 76 72 78 92 86 91 78 73 48 98 90 78 86 91 78 73 48 98 90 78 76 82 78 35 56 72 84 92 76 82 78 35 56 72 84 92 86 100 92 100 48 68 92 68 86 100 92 100 48 68 92 68 76 82 48 65 76 72 78 94 76 82 48 65 76 72 78 94 86 91 78 0 48 98 90 76 86 91 78 0 48 98 90 76 76 82 48 95 76 72 78 92 76 82 48 95 76 72 78 92 100 92 100 100 86 92 98 99 100 92 100 100 86 92 98 99

3. 11-3 Declaring Two-Dimensional Arrays  This data can be represented by an array of arrays  General Form type [][] identifier = new type [ rows ][ columns ] type [][] identifier = new type [ rows ][ columns ] type: a primitive type or reference type like String type: a primitive type or reference type like String identifier: reference to the two-dimensional array identifier: reference to the two-dimensional array rows: the number of rows allowed rows: the number of rows allowed columns: the number of columns in each row columns: the number of columns in each row  Example where all 80 elements are 0 int[][] quiz = new int[8][10];

4. 11-4 Referencing individual elements in a 2-D array  Reference to an element of a two-dimensional array requires two subscripts ( row and column) identifier [ row ] [ column ] identifier [ row ] [ column ]  Each subscript must be bracketed individually — [ row, column ] is an error — Examples: quiz[0][0] = 76; quiz[1][1] = 91; int sum = quiz[3][4] + quiz[6][7]; quiz[7][9]++;

5. 11-5 Can use array initializers Each of the 10 arrays has 8 integer elements int[][] quiz = { { 76, 82, 78, 85, 56, 72, 84, 92 }, { 86, 91, 92, 100, 48, 68, 92, 78 }, { 76, 82, 48, 95, 76, 72, 78, 92 }, { 86, 91, 78, 73, 48, 98, 90, 78 }, { 76, 82, 78, 35, 56, 72, 84, 92 }, { 86, 100, 92, 100, 48, 68, 92, 68 }, { 76, 82, 48, 65, 76, 72, 78, 94 }, { 86, 91, 78, 0, 48, 98, 90, 76 }, { 76, 82, 48, 95, 76, 72, 78, 92 }, { 100, 92, 100, 100, 86, 92, 98, 99 } }; assertEquals(76, quiz[0][0]); // upper left assertEquals(100, quiz[5][3]); // near middle assertEquals(99, quiz[9][7]); // lower right

6. 11-6 Can ask for rows and columns assertEquals(10, quiz.length); // rows assertEquals(8, quiz[0].length); // columns assertEquals(8, quiz[7].length); // columns

7. 11-7 Display elements row by row // Example of row by row processing for (int row = 0; row < quiz.length; row++) { // Display one row for (int col = 0; col < quiz[0].length; col++) { // Display each column of each row System.out.print(quiz[row][col] + " "); } System.out.println(); } Output 76 82 78 85 56 72 84 92 86 91 92 100 48 68 92 78 76 82 48 95 76 72 78 92 86 91 78 73 48 98 90 78 76 82 78 35 56 72 84 92 86 100 92 100 48 68 92 68 76 82 48 65 76 72 78 94 86 91 78 0 48 98 90 76 76 82 48 95 76 72 78 92 100 92 100 100 86 92 98 99

8. 11-8 Other example code  See Chapter 11 for more examples of row by row processing and column by column processing using nested for loops  Continue code demo with class Matrix