Lecture 9/3/11: Contents

1. Lecture 9/3/11: Contents • Array of user-defined objects • 2D array

2. User defined type reading Follows such classes as: - Oblong and OblongTester, sections 6.3 and 7.2, Charatan and Kans, “Java in two semesters” - Counter and CounterTest, sections 6.3-6.6, Pohl and McDowell, “Java by dissection” - Employee and TwoEmployee, p. 96-112, Ch.3, Farrell, “Java programming”

3. Array of user-defined type(1) • The setting: We have a number of applicants for whom we have separate, but matching, lists of names and id’s organised as arrays. • We would like to develop a new type for an Applicant to hold all individual data of the applicant, in this case just id and name, but it can have as many attributes as it takes. • With this new type, we would like to organise a list of applicants as an array of this type

4. Array of user-defined type(2) • To develop an array of applicants, we need • The ID and name arrays (A); • A named class, say Appl, with variables declared to hold all individual applicant data (B); • A constructor in this class that would take values from the arrays holding ID and name information (C); • Generation of an instance of array of new type, Appl (D); • Feeding the ID’s and names into the Appl array (E); • We can show that this does work by printing out data of all the entries in the Appl array

5. Array of user-defined type(3) • class Appl{ • public int ids; • public String nms; • public Appl(int iden, String nnn){ • ids=iden; • nms=nnn;} //constructor • static int[] iden(){ • int ii[]={12, 15, 22, 18, 11}; • return ii;} // method producing array of IDs • static String[] namen(){ • String jj[]={"Aa", "Bb", "Cc", "Dd", "Ee"}; • return jj;} // method producing array of names

6. Array of user-defined type(4) • public static void main(String[] args){ • int id[]=iden(); • String name[]=namen(); • Appl[] many=new Appl[id.length]; • for(int i=0;i<id.length;i++) • many[i]=new Appl(id[i],name[i]); • //many – array of Appl type objects. Check: • for(int i=0;i<name.length;i++){ • System.out.println(i +"th applicant data:"); • System.out.println("Id: "+many[i].ids); • System.out.println("Name: "+many[i].nms); • System.out.println(); } • } • }

7. Array of user-defined type(5) Question: • Identify which parts of class Appl correspond • to tasks A, B, C, D and E on slide 4

8. 2D arrays The last subject to study in SP1

9. 2D arrays: example Example - week sales at each of four shops:            Sunday                     Days        0        1     2      3     4      5      6  |----------------------------------------------------0|        22     49     4     93     0     12     32  | 1|         3        8     67   51     5      3     63 |2|         14      8     23   14     5     23     16  | 3|         54      0     76   31     4      3     99

10. 2D arrays: actions Declaration and initialisation (with zeros): int[ ][ ] sales = new int[4][7]; Filling in: sales = {                {22, 49, 4, 93, 0, 12, 32},                  ………………………,                 {54, 0, 76, 31, 4, 3, 99}              }

11. 2D arrays: accessing Reaching a component: sales[2][5] = 23 or int aa = 2; int bb = 5; sales[aa][bb]=23 sales[bb][aa] = ?(answer: error) because sales[5][2] does not exist

12. 2D arrays: processing Summary sales: •     int sum =0; •     for (int shop = 0; shop < 4; shop ++) •     for(int day = 0; day < 7; day ++) •     sum = sum + sales[shop][day]; As a method:  public int sum( int[][] a) { •  int total = 0; • for (int row = 0; row < a.length; row ++) •  for( int col = 0; col < a[0].length; col ++) •  total = total + a [row][col]; •                     return total;               }

13. 2D arrays: different row lengths Different row lengths: int[ ] Twodarray={{1, 1, 1}, {1, 3}, {4,5,4,5}} Modifying the summation method:  public int sum( int[][] a) { •  int total = 0; • for (int row = 0; row < a.length; row ++) •   for( int col = 0; col < a[row].length; col ++) •   total = total + a[row][col]; •         return total;               } • int summa=sum(Twodarray);//application of the method

14. Two-dimensional arrays Summary sales for Wednesday (4th day): •         int sum =0; •         for (int row=0; row< 4; row ++) •         sum = sum + sales[row][3]; Further problems: • methods: • summary sales on Wednesday (next page) • summary sales by week-day (after next page) • summary sales by shop

15. Summary sales on any day Method: summary sales in sales[][] on any day   int sss(sales[][], int day){ int sum =0;    for (int r=0; r<sales.length; r++)       sum = sum + sales[r][day]; return sum;}

16. Summary sales on all days: method int[] sss(sales[][], int day){//note: output is an array! int[] sum =new int[sales[0].length]; for (int c=0; c<sales[0].length; c++)    for (int r=0; r<sales.length; r++) sum[c] = sum[c] + sales[r][c]; return sum;}