1. Multidimensional Arrays

2. Multidimensional Arrays
Arrays are good for storing lists of data
What about storing a table? 14 8 9 7 78 90 89 70 09 79 87 97 07 08 77 67 56 65 45 30 91 39 37 38 20 27 24 28 80 46 72

3. Multidimensional Arrays
If arrays can store any object, why not have them store arrays?
An array of arrays is a list of lists, or a table!

4. Multidimensional Arrays
2D array declaration:
<data type>[ ][ ] <name>;
int[ ][ ] grades;
String[ ][ ] seatingChart;
2D array definition:
grades = new int[9][15];
seatingChart = new String[5][9];
Remember, each reference in seatingChart must be initialized!

5. Multidimensional Arrays
Accessing elements:
grades[0][0] = 90; 1 2 3 4 5 6 7 90

6. Multidimensional Arrays
Accessing elements:
grades[0][0] = 90;
Grades[8][5] = 65; 1 2 3 4 5 6 7 90 65

7. Multidimensional Arrays
for(int i=0; i< grades.length; i++)
for(int j=0; j< grades[i].length; j++)
averages[i] += grades[i][j]; 1 2 3 4 5 6 7 90 34 65 87 78 57 98 77 88 99 43 76 45 44 67 89 82 92 17 95

8. Multidimensional Arrays
How are 2D arrays really stored? 1 2 3 90 34 65 78 57 98 87

9. Multidimensional Arrays
How are 2D arrays really stored?
2D arrays are arrays of arrays 1 2 3 90 34 65 78 57 98 87

10. Multidimensional Arrays
How are 2D arrays really stored?
2D arrays are arrays of arrays 90 34 65 1 2 3 1 2 3 90 34 65 78 57 98 87 78 57 98 34 65 87 57 98 87

11. Multidimensional Arrays
grades[0][1] = 90 34 65 1 2 3 1 2 3 90 34 65 78 57 98 87 78 57 98 34 65 87 57 98 87

12. Multidimensional Arrays
grades[0][1] = 90 34 65 1 2 3 1 2 3 90 34 65 78 57 98 87 78 57 98 34 65 87 57 98 87

13. Multidimensional Arrays
grades[0][1] = 90 34 65 1 2 3 1 2 3 90 34 65 78 57 98 87 78 57 98 34 65 87 57 98 87

14. Multidimensional Arrays
grades[0][1] = 90 34 65 1 2 3 1 2 3 90 34 65 78 57 98 87 78 57 98 34 65 87 57 98 87

15. Multidimensional Arrays
grades[0][1] = 34 90 34 65 1 2 3 1 2 3 90 34 65 78 57 98 87 78 57 98 34 65 87 57 98 87

16. Multidimensional Arraysj
for(int i=0; i< grades.length; i++)
for(int j=0; j< grades[i].length; j++)
averages[i] += grades[i][j]; 90 34 65 1 2 3 1 2 3 90 34 65 78 57 98 87 78 57 98 34 65 87 57 98 87

17. Multidimensional Arraysj
for(int i=0; i< grades.length; i++)
for(int j=0; j< grades[i].length; j++)
averages[i] += grades[i][j]; 90 34 65 1 2 3 1 2 3 90 34 65 78 57 98 87 78 57 98 34 65 87 57 98 87

18. Multidimensional Arraysj
for(int i=0; i< grades.length; i++)
for(int j=0; j< grades[i].length; j++)
averages[i] += grades[i][j]; 1 90 34 65 1 2 3 1 2 3 90 34 65 78 57 98 87 78 57 98 34 65 87 57 98 87

19. Multidimensional Arraysj
for(int i=0; i< grades.length; i++)
for(int j=0; j< grades[i].length; j++)
averages[i] += grades[i][j]; 2 90 34 65 1 2 3 1 2 3 90 34 65 78 57 98 87 78 57 98 34 65 87 57 98 87

20. Multidimensional Arraysj
for(int i=0; i< grades.length; i++)
for(int j=0; j< grades[i].length; j++)
averages[i] += grades[i][j]; 1 90 34 65 1 2 3 1 2 3 90 34 65 78 57 98 87 78 57 98 34 65 87 57 98 87

21. Multidimensional Arraysj
for(int i=0; i< grades.length; i++)
for(int j=0; j< grades[i].length; j++)
averages[i] += grades[i][j]; 1 1 90 34 65 1 2 3 1 2 3 90 34 65 78 57 98 87 78 57 98 34 65 87 57 98 87

22. Multidimensional Arraysj
for(int i=0; i< grades.length; i++)
for(int j=0; j< grades[i].length; j++)
averages[i] += grades[i][j]; 1 2 90 34 65 1 2 3 1 2 3 90 34 65 78 57 98 87 78 57 98 34 65 87 57 98 87

23. Multidimensional Arrays
Although we can think of it in table format for accessing, it is not necessarily a table!
int [ ][ ][ ] threeD = new int[10][ ][ ];
threeD[10] = new int [10][ ];
threeD[10][5] = new int[7];
threeD[10][5][4] = 6;
What is the Memory Diagram?

24. Multidimensional Arrays
int [ ][ ][ ] threeD = new int[10][ ][ ];
threeD[9] = new int [10][ ];
threeD[9][5] = new int[7];
threeD[9][5][4] = 6; 1 2 3 4 5 6 7 8 9

25. Multidimensional Arrays
int [ ][ ][ ] threeD = new int[10][ ][ ];
threeD[9] = new int [10][ ];
threeD[9][5] = new int[7];
threeD[9][5][4] = 6; 1 2 3 4 5 6 7 8 9

26. Multidimensional Arrays
int [ ][ ][ ] threeD = new int[10][ ][ ];
threeD[9] = new int [10][ ];
threeD[9][5] = new int[7];
threeD[9][5][4] = 6; 1 2 3 4 5 6 7 8 9

27. Multidimensional Arrays
int [ ][ ][ ] threeD = new int[10][ ][ ];
threeD[9] = new int [10][ ];
threeD[9][5] = new int[7];
threeD[9][5][4] = 6; 1 2 3 4 5 6 7 8 9 6

28. Multidimensional Arrays
Exercise:
Write a method that takes an int n, and returns the multiplication table (2D array) for all numbers from
1 to n

29. Multidimensional Arrays
public static int[ ][ ] multTable(int n){
int[ ][ ] table = new int[n][n];
for(int i=1; i <= n; i++)
for(int j=1; j<=n; j++)
table[i][j] = i*j;
return table; }