Multidimensional%20Arrays

1

• Multidimensional Arrays

2
Multidimensional Arrays

• Arrays are good for storing lists of data
• What about storing a table?

14 8 9 8 7 78 90 89 70 70 7 09 09 09
79 70 87 97 07 87 89 90 7 87 7 70 87 09
70 70 7 09 09 09 89 09 89 08 77 78 8 67
87 56 65 45 30 91 70 39 37 30 37 08 37 38
89 20 89 78 27 87 24 27 78 28 27 89 78 80
80 89 89 89 89 89 78 46 45 70 20 9 7 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
• ltdata typegt ltnamegt
• int grades
• String seatingChart
• 2D array definition
• grades new int915
• seatingChart new String59
• Remember, each reference in seatingChart must be
  initialized!

5
Multidimensional Arrays

• Accessing elements
• grades00 90

0 1 2 3 4 5 6 7
8 9 10 11 12 13 14
0 1 2 3 4 5 6 7
90








6
Multidimensional Arrays

• Accessing elements
• grades00 90
• Grades85 65

0 1 2 3 4 5 6 7
8 9 10 11 12 13 14
0 1 2 3 4 5 6 7
90





65


7
Multidimensional Arrays

• for(int i0 ilt grades.length i)
• for(int j0 jlt gradesi.length j)
• averagesi gradesij

0 1 2 3 4 5 6 7
8 9 10 11 12 13 14
0 1 2 3 4 5 6 7
90 34 65 87 65 78 57 98 87 65 77 88 99 43 76
78 57 98 87 65 77 90 34 65 87 65 78 57 77 88
34 65 87 65 87 65 78 57 77 87 65 78 45 76 44
57 98 87 65 34 65 87 65 78 57 98 87 65 77 88
65 77 90 34 65 87 65 78 78 57 98 87 65 77 77
87 65 78 57 77 87 76 67 89 82 92 17 95 98 87
78 57 98 87 65 77 90 34 65 87 76 67 89 82 65
87 65 78 77 87 76 67 89 82 92 17 65 77 90 34
57 98 87 65 34 65 78 57 98 87 65 77 65 34 65
8
Multidimensional Arrays

• How are 2D arrays really stored?

0 1 2
0 1 2 3
90 34 65
78 57 98
34 65 87
57 98 87
9
Multidimensional Arrays

• How are 2D arrays really stored?
• 2D arrays are arrays of arrays

0 1 2
0 1 2 3
90 34 65
78 57 98
34 65 87
57 98 87
10
Multidimensional Arrays

• How are 2D arrays really stored?
• 2D arrays are arrays of arrays

0 1 2
90 34 65
0 1 2
0 1 2 3
0 1 2 3
0 1 2
90 34 65
78 57 98
34 65 87
57 98 87




78 57 98
0 1 2
34 65 87
0 1 2
57 98 87
11
Multidimensional Arrays

• grades01

0 1 2
90 34 65
0 1 2
0 1 2 3
0 1 2 3
0 1 2
90 34 65
78 57 98
34 65 87
57 98 87




78 57 98
0 1 2
34 65 87
0 1 2
57 98 87
12
Multidimensional Arrays

• grades01

0 1 2
90 34 65
0 1 2
0 1 2 3
0 1 2 3
0 1 2
90 34 65
78 57 98
34 65 87
57 98 87




78 57 98
0 1 2
34 65 87
0 1 2
57 98 87
13
Multidimensional Arrays

• grades01

0 1 2
90 34 65
0 1 2
0 1 2 3
0 1 2 3
0 1 2
90 34 65
78 57 98
34 65 87
57 98 87




78 57 98
0 1 2
34 65 87
0 1 2
57 98 87
14
Multidimensional Arrays

• grades01

0 1 2
90 34 65
0 1 2
0 1 2 3
0 1 2 3
0 1 2
90 34 65
78 57 98
34 65 87
57 98 87




78 57 98
0 1 2
34 65 87
0 1 2
57 98 87
15
Multidimensional Arrays

• grades01 34

0 1 2
90 34 65
0 1 2
0 1 2 3
0 1 2 3
0 1 2
90 34 65
78 57 98
34 65 87
57 98 87




78 57 98
0 1 2
34 65 87
0 1 2
57 98 87
16
Multidimensional Arrays
i
j

• for(int i0 ilt grades.length i)
• for(int j0 jlt gradesi.length j)
• averagesi gradesij

0
0
0 1 2
90 34 65
0 1 2
0 1 2 3
0 1 2 3
0 1 2
90 34 65
78 57 98
34 65 87
57 98 87




78 57 98
0 1 2
34 65 87
0 1 2
57 98 87
17
Multidimensional Arrays
i
j

• for(int i0 ilt grades.length i)
• for(int j0 jlt gradesi.length j)
• averagesi gradesij

0
0
0 1 2
90 34 65
0 1 2
0 1 2 3
0 1 2 3
0 1 2
90 34 65
78 57 98
34 65 87
57 98 87




78 57 98
0 1 2
34 65 87
0 1 2
57 98 87
18
Multidimensional Arrays
i
j

• for(int i0 ilt grades.length i)
• for(int j0 jlt gradesi.length j)
• averagesi gradesij

0
1
0 1 2
90 34 65
0 1 2
0 1 2 3
0 1 2 3
0 1 2
90 34 65
78 57 98
34 65 87
57 98 87




78 57 98
0 1 2
34 65 87
0 1 2
57 98 87
19
Multidimensional Arrays
i
j

• for(int i0 ilt grades.length i)
• for(int j0 jlt gradesi.length j)
• averagesi gradesij

0
2
0 1 2
90 34 65
0 1 2
0 1 2 3
0 1 2 3
0 1 2
90 34 65
78 57 98
34 65 87
57 98 87




78 57 98
0 1 2
34 65 87
0 1 2
57 98 87
20
Multidimensional Arrays
i
j

• for(int i0 ilt grades.length i)
• for(int j0 jlt gradesi.length j)
• averagesi gradesij

1
0
0 1 2
90 34 65
0 1 2
0 1 2 3
0 1 2 3
0 1 2
90 34 65
78 57 98
34 65 87
57 98 87




78 57 98
0 1 2
34 65 87
0 1 2
57 98 87
21
Multidimensional Arrays
i
j

• for(int i0 ilt grades.length i)
• for(int j0 jlt gradesi.length j)
• averagesi gradesij

1
1
0 1 2
90 34 65
0 1 2
0 1 2 3
0 1 2 3
0 1 2
90 34 65
78 57 98
34 65 87
57 98 87




78 57 98
0 1 2
34 65 87
0 1 2
57 98 87
22
Multidimensional Arrays
i
j

• for(int i0 ilt grades.length i)
• for(int j0 jlt gradesi.length j)
• averagesi gradesij

1
2
0 1 2
90 34 65
0 1 2
0 1 2 3
0 1 2 3
0 1 2
90 34 65
78 57 98
34 65 87
57 98 87




78 57 98
0 1 2
34 65 87
0 1 2
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 int10
• threeD10 new int 10
• threeD105 new int7
• threeD1054 6
• What is the Memory Diagram?

24
Multidimensional Arrays

• int threeD new int10
• threeD9 new int 10
• threeD95 new int7
• threeD954 6

0 1 2 3 4 5 6 7 8 9
25
Multidimensional Arrays

• int threeD new int10
• threeD9 new int 10
• threeD95 new int7
• threeD954 6

0 1 2 3 4 5 6 7 8 9
0 1 2 3 4 5 6 7 8
9

26
Multidimensional Arrays

• int threeD new int10
• threeD9 new int 10
• threeD95 new int7
• threeD954 6

0 1 2 3 4 5 6 7 8 9
0 1 2 3 4 5 6 7 8
9

0 1 2 3 4 5 6

27
Multidimensional Arrays

• int threeD new int10
• threeD9 new int 10
• threeD95 new int7
• threeD954 6

0 1 2 3 4 5 6 7 8 9
0 1 2 3 4 5 6 7 8
9

0 1 2 3 4 5 6
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 intnn
• for(int i1 i lt n i)
• for(int j1 jltn j)
• tableij ij
• return table