CS 200 Branches

1. CS 200 Branches Jim Williams, PhD

2. This Week • Piazza: notes • Consulting Hours: Request Help Queue • Team Lab: take paper, draw pictures • Thursday: • 3 parts to P3 due • Pre-Exam 1: bring WISC ID, #2 Pencils • 6 questions, 15 minutes • Lecture: Using Objects, Branches

3. Read In Values Using Scanner Whitespace: space, tab, newline Token: a sequence of non-whitespace characters. 14 23.0 hello This, is a sentence. 2nd line 3rd line 43

4. Some Scanner Methods • Read next token: nextInt(), nextDouble(), next() • Read through next newline and return everything read prior to newline. nextLine()

5. What is the value in name? String note = "1 \n2\nAlex two words"; Scanner input = new Scanner( note); int num1 = input.nextInt(); int num2 = input.nextInt(); String words = input.nextLine(); String name = input.next();

6. What are values of variables? String note = "Minsub\n22\nCS"; Scanner input = new Scanner( note); String name = input.nextLine(); int age = input.nextInt(); String major = input.nextLine();

7. What are values of variables? String note = "Minsub\n22\nCS"; Scanner input = new Scanner( note); String name = input.nextLine(); int age = input.nextInt(); input.nextLine(); //read and ignore rest of line String major = input.nextLine();

8. What are values of variables? String note = "20 25\nscores"; Scanner input = new Scanner( note); int score1 = input.nextInt(); int score2 = input.nextInt(); String title = input.nextLine();

9. What is value in str3? String note = " C S\n2 \n33\n end\n"; Scanner input = new Scanner( note); String str1 = input.nextLine(); int num1 = input.nextInt(); String str2 = input.next(); String str3 = input.nextLine();

10. String class • A reference type (instantiable class), not a primitive data type. final String TITLE_PREFIX = "Week "; String title = TITLE_PREFIX + 3; title = "new title"; System.out.println( title); • Draw a picture

11. String String name2 = "Alex"; name2.toUpperCase(); String name3 = name2 + " Johnson"; System.out.print( name3); • instances of String are immutable(cannot change) • methods in String classthat appear may change strings actuallyreturn new strings.

12. What does aChar contain? String strA = "This is a string"; char aChar = strA.charAt( 3);

13. Relational and Equality Operators < <= > >= == != int n = 6; boolean result = n != 5;

14. Logical Operators && (AND) both sides true to be true, else false || (OR) either side true then true, else false ! (NOT) if true then false, and vice-versa Is !(a && b) equivalent to !a || !b ?

15. What is returned value? static boolean something(boolean flag) { return !flag != false; } Truth Table:

16. !(a && b) equivalent? !a || !b Truth Table:

17. null Literal null • a literal that can be assigned to any reference variable. Means no-reference or refers to nothing. • Example: String str = null;

18. What happens? String str = null; char ch = str.charAt(1);

19. Comparing: == vs equals() • Primitive data types • use == for comparing primitive values • No equals() method for primitive data types • Reference data types • use == for comparing references • use equals() for comparing instance/object contents • The meaning of equals() depends on the class it is defined in.

20. What is printed out? int i = 6; int j = 6; System.out.println( i == j); System.out.println( i.equals( j)); Integer k = new Integer( 7); Integer m = new Integer( 7); System.out.println( k == m); System.out.println( k.equals( m));

21. Values of a1 and a2? char ch1 = 'H'; String str = "Hello"; char ch2 = str.charAt(0); boolean a1 = ch1 == ch2; boolean a2 = ch1.equals(ch2);

22. String: == vs equals() String str1 = "hello"; String str2 = "hello"; String str3 = new String("hello"); String str4 = "hello"; System.out.println( str1 == "hello" ); System.out.println( str1 == str2); System.out.println( str1.equals("hello")); System.out.println( str3 == str1); System.out.println( str3.equals( str2));

23. Thursday • preExam, lecture Branches • Sit in columns with space between (if possible)

24. Eclipse IDE

25. Are these equivalent? boolean tired = true; if ( tired) { //take break tired = false; } if ( !tired) { //keep working } boolean tired = true; if ( tired) { //take break tired = false; } else { //keep working }

26. Floating Down a River http://www.thehiltonorlando.com/discover/pools-and-lazy-river/

27. Side Trip, maybe multiple side trips boolean tired = true; if ( tired) { System.out.println(“take break”); }

28. One side of the Island or the other boolean sunny = false; if ( sunny) { System.out.print(“sunny”); } else { System.out.print(“not sunny”); } System.out.println( “ and back together”);

29. Equivalent? char chr = //any valid char out = 'W'; if ( chr == 'A') { out = 'X'; } if ( chr == 'B') { out = 'Y'; } if ( chr != 'A' || chr != 'B') { out = 'Z'; } char chr = //any valid char out = 'W'; if ( chr == 'A') { out = 'X'; } else if ( chr == 'B') { out = 'Y'; } else { out = 'Z'; }

30. Switch: What is printed out? char choice = 'a'; switch (choice) { case 'a': System.out.print("a"); case 'b': System.out.print("b"); break; default: System.out.print("other"); break; }

31. What is the value of msg? boolean flag = true; String msg = "before if"; if ( flag) { msg = "" + flag; }

32. Scanner Scanner input = new Scanner("1 \ntwo \n 2\n\n"); int a = input.nextInt(); if ( input.hasNextInt()) { int b = input.nextInt(); } else { input.nextLine(); } String line = input.nextLine(); System.out.println("#" + line + "#");

33. Scanner String note = "Hmm\na \na\n3\n\nline note."; Scanner input = new Scanner( note); int num = 0; String str1 = input.nextLine(); String str2 = input.next(); if ( input.hasNextInt()) { num = input.nextInt(); } String str4 = input.nextLine();

34. Debugging with Print statements See what is going on. Divide and conquer.