1. String & Exception

2. Lesson plan Class & Object String Exercise for midterm

3. Class & Object A class definition provides a description of a typical object within that class. An individual object is an instance of a class. A class has its behavior (methods) and attributes (fields).

4. Class & Object Access a dynamic method or field by:. Example: df.format(loanAmount). Access a static method by. Example: JOptionPane. showInputDialog(null,"Loan Amount (dollars.cents):");

5. String What is it? –A String is a sequence of characters that is treated as a single value –String class handles all operations related to String –String class is defined in java.lang.

6. Create a String object Syntax: String ; =new String(“constant”); OR String ; = “constant”

7. Create a String object Example: String strVar; strVar = new String(“CS 172 Course”); OR String strVar; strVar = “CS 172 Course”;

8. Internal Representation of a String Individual characters in a string object are indexed from 0

9. Compute Length of a string Method: length() Returns the length of a string Example: String strVar; strVar = new String(“CS 172 Course”); int len = strVar.length();

10. Substring Method: Extract a substring from a given string by specifying the beginning and ending positions Example: String strVar, strSubStr; strVar = new String(“CS 172 Course”); strSubStr = strVar.substring(0,6); strSubStr =“CS 172”

11. Index position of a substring within another string Method: Find an index position of a substring within another string. Example: String strVar1 = “CS 172 Course”; String strVar2 = “Course”; int index; index = strVar1.indexOf(strVar2); index = 7

12. Index position of a substring within another string Example: String strVar1 = “CS 172 Course”; String strVar2 = “C”; int index; index = strVar1.indexOf(strVar2); index = 0

13. String concatenation Method: Create a new string from two strings by concatenating the two strings. Example: String strVar1 = “CS 172”; String strVar2 = “Course”; String sumStr; sumStr = strVar1+strVar2;

14. Practice exercise Determine values of some variables given codes

15. String comparison Two methods: equals equalsIgnoreCase string1.equals(string2) Or string1.equalsIgnoreCase(string2)

16. String comparison Methods: equals equalsIgnoreCase compareTo String string1 =“CS 172”; String string2 = “172” Boolean isEqual; isEqual = string1.equals(string2); isEqual= false

17. String comparison equalsIgnoreCase Example: String string1 =“COMPSCI”; String string2 = “compsci” Boolean isEqual; isEqual = string1.equals(string2); isEqual= true

18. String comparison compareTo Example: String string1 =“Adam”; String string2 = “Brian” int compareResult; compareResult = string1.compareTo(string2); compareResult < 0

19. String comparison - string1.compareTo(string2) Compares two strings lexicographically will return 0 if two strings are equal will return negative value if string1 is less than string 2 will return positive value if string1 is greater than string 2 The comparison is based on the Unicode value of each character in the strings

20. String comparison The comparison is based on the Unicode value of each character in the strings let k be the smallest index valid for both strings; compareTo returns the difference of the two character values at position k in the two string - - that is, the value: character at the position k of string 1 – character at the position k of string 2

21. Character at position k of a string Example: String sample=“CS 172 Course”; char aChar; aChar = sample.charAt(3) aChar=‘1’

22. Character at position k of a string Example: String sample=“CS 172 Course”; char aChar; aChar = sample.charAt(3) aChar=‘1’

23. Implicit type of conversion Implicit type conversion is common: Example: int num = 172; String s = “CS "+num; s=“CS 172”

24. Practice (answers) Monday (3) int sum1 = 0; for (int i=0; i<= 5; i++) for (int j=0; j<= 5; j++) { sum1+=i; } System.out.println(" Sum1 is "+ sum1); i=0 j=0 -> sum1 = 0+i = 0+0 = 0 j=1 -> sum1 = 0+i = 0+0 = 0 ….. j=5 -> sum1 = 0+i = 0+0 = 0 i=1 j=0 -> sum1 = 0+i=0+1=1 j=1 -> sum1= 0+1+ i =0+1*2 … j=5 -> sum1 = 0+1*6 = 6

25. Practice (answers) Monday (3) i=2 j=0 -> sum1 = 6+i = 6+2*1 j=1 -> sum1 = 6+2+2= 6+2*2 ….. j=5 -> sum1 = 6+i = 6+2*6 = 18 i=3 j=0 -> sum1 = 18+3 = 18+3*1 j=1 -> sum1 = 18+3+3= 18+3*2 ….. j=5 -> sum1 = 18+3*6= 36 i=4 j=0 -> sum1 = 36+4*1 j=1 -> sum1 = 36+4*2 ….. j=5 -> sum1 = 36+4*6= 60 i=5 j=0 -> sum1 = 60+5*1 j=1 -> sum1 = 60+5*2 ….. j=5 -> sum1 = 60+5*6= 90 SUM1= 90

26. Practice (answers) Wednesday (3) int sum =0; int j=0; while (j<11) { j++; int i=5; while (i>j) { sum = sum + (i+j); i--; } System.out.println(“ Sum = “+ sum);

27. Practice (answers) Wednesday (3) j=0 j= 1 i=5 sum = sum +(1+5) = 6 i=4 sum = sum + (1+4) = 6+5 = 11 i=3 sum = sum + (1+3) = 11+4 = 15 i=2 sum = sum+(1+2) = 15+3 = 18

28. Practice (answers) Wednesday (3) j= 2 i=5 sum = sum +(2+5) = 18+7 = 25 i=4 sum = sum + (2+4) =25+ 6 = 31 i=3 sum = sum + (2+3) = 31+5= 36

29. Practice (answers) Wednesday (3) j= 3 i=5 sum = sum +(3+5) = 36+8 = 44 i=4 sum = sum + (3+4) =44+ 7 = 51

30. Practice (answers) Wednesday (3) j= 4 i=5 sum = sum +(4+5) = 51+9 = 60

31. Practice Write a loop that prints out a string in reverse. input: “CS 172” output: “271 SC”

32. Practice public class StringReverse{ public static void main(String[] args) { String strSource ="CS 172"; String strDes=""; int len = strSource.length()-1; for (int i=len; i>=0; i--) strDes = strDes + strSource.charAt(i); System.out.println(" Reserve string is "+ strDes); }

33. Practice Multiple choices Determine the output of the codes

34. StringBuffer class A String object is immutable. Once it is created, we can’t add/delete/modify characters of a String object If we need to modify the content of a string directly, we must use StringBuffer class

35. Create a StringBuffer object StringBuffer word = new StringBuffer(“Java”); word.setCharAt(0,’D’); word.setCharAt(1,’i’); word = DIVA

36. Create a StringBuffer object StringBuffer word = new StringBuffer(“Java”); word.setCharAt(0,’D’); word.setCharAt(1,’i’); word = “DIVA”

37. Delete a substring from a StringBuffer object StringBuffer word = new StringBuffer(“CS172 Course”); word.delete(0,1); word = “172 Course”

38. Append a string StringBuffer word = new StringBuffer(“CS172”); word.append(“Course”); word = “172 Course”

39. Insert a string StringBuffer word = new StringBuffer(“CS Course”); word.insert(3,“172”); word = “CS 172 Course”

40. Practice Write a method to sort three strings alphabetically

41. Practice Identify objects, class What will be the output from the following code?