Professor: Alvin Chao

Transcription

1 Professor: Avin Chao

2 CS149 For Each and Reference Arrays

3 Looping Over the Contents of an Array We often use a for oop to access each eement in an array: for (int i = 0; i < names.ength; i++) { System.out.printn("Heo " + names[i]); If ony there were a better way

4 Enhanced For Loop (aso caed a for each oop) This oop does the same thing as the oop on the previous side: This variabe wi be assigned the eements from this array for (String name : names) { System.out.printn("Heo " + name); This code is shorter, easier to understand, ess errorprone

5 When To Use an Enhanced For Loop Aways Uness you can't: Need to modify the array Need to know the eement index for some reason Need to process the eements out of order...

6 Exercise #1 1)What wi be printed by the foowing code? 2)Where is the stye probem in this code? String[] summer= {"June", "Juy", "August"; String etters = ""; for (String i : summer) { etters += i.charat(0); System.out.printn(etters);

7 Exercise #1 1)What wi be printed by the foowing code? 1)JJA 2)Where is the stye probem in this code? String[] summer= {"June", "Juy", "August"; String etters = ""; for (String i : summer) { etters += i.charat(0); System.out.printn(etters); This is not an index variabe, it requires a meaningfu name (ike month ).

8 Exercise #2 Compete the foowing method using an enhanced for oop (reminder: use.equas to compare strings.) /** * This method counts the number of times a target word occurs in * an array of words. Comparisons are case-sensitive. * words - The array to search target - The word to search for The word count */ pubic static int countword(string[] words, String target) {

9 Exercise #2 Compete the foowing method using an enhanced for oop: /** * This method counts the number of times a target word occurs in * an array of words. Comparisons are case-sensitive. * words - The array to search target - The word to search for The word count */ pubic static int countword(string[] words, String target) { int count = 0; for (String curword : words) { if (curword.equas(target)) { count++; return count;

10 Reference Arrays [0] = new Die(6); [2] = new Die(5); if (curdie!= ) { curdie.ro();

11 Reference Arrays [0] = new Die(6); [2] = new Die(5); if (curdie!= ) { curdie.ro();

12 Reference Arrays [0] = new Die(6); [2] = new Die(5); Die face: 6 if (curdie!= ) { curdie.ro();

13 Reference Arrays [0] = new Die(6); [2] = new Die(5); Die face: 6 if (curdie!= ) { curdie.ro(); Die face: 5

14 Exercise #3 Draw the memory diagram and determine output. Die singe; singe = new Die(1); for (int i = 0; i <.ength; i++) { [i] = singe; [0].setFace(3); System.out.printn(curDie.getFace());

15 Exercise #3 Draw the memory diagram and determine output. Die singe; singe singe = new Die(1); for (int i = 0; i <.ength; i++) { [i] = singe; [0].setFace(3); System.out.printn(curDie.getFace());

16 Exercise #3 Draw the memory diagram and determine output. Die singe; singe singe = new Die(1); for (int i = 0; i <.ength; i++) { [i] = singe; [0].setFace(3); System.out.printn(curDie.getFace());

17 Exercise #3 Draw the memory diagram and determine output. Die singe; singe singe = new Die(1); for (int i = 0; i <.ength; i++) { [i] = singe; [0].setFace(3); System.out.printn(curDie.getFace());

18 Exercise #3 Draw the memory diagram and determine output. Die singe; singe = new Die(1); singe Die face: 1 for (int i = 0; i <.ength; i++) { [i] = singe; [0].setFace(3); System.out.printn(curDie.getFace());

19 Exercise #3 Draw the memory diagram and determine output. Die singe; singe = new Die(1); singe Die face: 1 for (int i = 0; i <.ength; i++) { [i] = singe; [0].setFace(3); System.out.printn(curDie.getFace()); i 0

20 Exercise #3 Draw the memory diagram and determine output. Die singe; singe = new Die(1); singe Die face: 1 for (int i = 0; i <.ength; i++) { [i] = singe; [0].setFace(3); System.out.printn(curDie.getFace()); i 0

21 Exercise #3 Draw the memory diagram and determine output. Die singe; singe = new Die(1); singe Die face: 1 for (int i = 0; i <.ength; i++) { [i] = singe; [0].setFace(3); System.out.printn(curDie.getFace()); i 1

22 Exercise #3 Draw the memory diagram and determine output. Die singe; singe = new Die(1); singe Die face: 1 for (int i = 0; i <.ength; i++) { [i] = singe; [0].setFace(3); i 1 System.out.printn(curDie.getFace());

23 Exercise #3 Draw the memory diagram and determine output. Die singe; singe = new Die(1); singe Die face: 1 for (int i = 0; i <.ength; i++) { [i] = singe; [0].setFace(3); i 2 System.out.printn(curDie.getFace());

24 Exercise #3 Draw the memory diagram and determine output. Die singe; singe = new Die(1); singe Die face: 1 for (int i = 0; i <.ength; i++) { [i] = singe; [0].setFace(3); System.out.printn(curDie.getFace()); i 2

25 Exercise #3 Draw the memory diagram and determine output. Die singe; singe = new Die(1); singe Die face: 1 for (int i = 0; i <.ength; i++) { [i] = singe; [0].setFace(3); System.out.printn(curDie.getFace()); i 3

26 Exercise #3 Draw the memory diagram and determine output. Die singe; singe = new Die(1); singe Die face: 1 for (int i = 0; i <.ength; i++) { [i] = singe; [0].setFace(3); System.out.printn(curDie.getFace()); i 3

27 Exercise #3 Draw the memory diagram and determine output. Die singe; singe = new Die(1); for (int i = 0; i <.ength; i++) { [i] = singe; [0].setFace(3); System.out.printn(curDie.getFace()); singe Die face: 3

28 Exercise #3 Draw the memory diagram and determine output. Die singe; singe = new Die(1); for (int i = 0; i <.ength; i++) { [i] = singe; [0].setFace(3); System.out.printn(curDie.getFace()); singe Die face: 3 Output :

29 Exercise #4 Compete the foowing method /** * This method creates a Die array, and popuates it with * Die objects. Each Die object wi be initiaized with * a random face vaue (using the zero argument constructor). * numdice - The number of Die objects in the new array The array of Die objects */ pubic static Die[] createdice(int numdice) {

30 Exercise #4 Compete the foowing method /** * This method creates a Die array, and popuates it with * Die objects. Each Die object wi be initiaized with * a random face vaue (using the zero argument constructor). * numdice - The number of Die objects in the new array The array of Die objects */ pubic static Die[] createdice(int numdice) { Die[] = new Die[numDice]; for (int i = 0; i <.ength; i++) { [i] = new Die(); return ;

31 Acknowedgements Parts of this activity are based on materias deveoped by Chris Mayfied and Nathan Sprague. </end>