1. CSCI 1226 Fall 2014 Reviews Section B

2. Computers  Types of computers:  Personal computers  Embedded systems  Servers  Hardware:  I/O devices: mice, keyboards, monitors, etc  CPU (Central Processing Unit)  Memory, Main/Primary vs secondary Exam tip! Examples of each type? Exam tip! Examples of each type? Exam tip! What are the differences? Exam tip! What are the differences?

3. …Computers  Software:  Data & instructions »Algorithm »Pseudo-code  Data hierarchy: »8 bits  byte »1 or more bytes  data value (field) »1 or more data values/objects  object (record) »data may be stored on secondary memory (file) Exam tip! What are the differences? Exam tip! What are the differences? Exam tip! An object can contain other objects! Exam tip! An object can contain other objects!

4. Java Programming Basics  IDE: Integrated Development Environment  Variables:  Data types  Naming rules and conventions  Math and special assignment operators  +, -, *, /, %  +=, -=, *=, /=. %=  ++, --

5. …Java Programming Basics  Output:  System.out.println() and System.out.print() »Print spaces »With or without quotes »Concatenation (using +, with math expressions, etc)  User input:  Scanner class: instantiation, import, etc  next(), nextLine(), nextInt(), nextDouble(), etc  Use nextLine() to »flush the input buffer Exam tip! How to pause a program using nextLine()? See Utilities.java Exam tip! How to pause a program using nextLine()? See Utilities.java Exam tip! Print all values in one line or each value in one line Exam tip! Print all values in one line or each value in one line

6. Conditionals  Syntax:  if, if-else, if-else if, if-else if … else  Comparison operators  ==, !=,, =  Logical operators  && (AND), || (OR), ! (NOT)

7. … Conditionals  Sequential and nested if-else:  Convert one to the other  What’s the output?:  What’s the code?  Possible outcomes:  outcome #1: A, B, C, E, F  outcome #2: A, D, E, F System.out.print(“A”); if (...) { System.out.print(“B”); } if (...) { System.out.print(“C”); if (...) { System.out.print(“D”); } else { System.out.print(“E”); }

8. boolean variables  Can save the answer to a comparison  use a boolean variable boolean workedOvertime = (hours > 40); »you don’t need parentheses, but it’s easier to read  E.g.) Write Boolean expressions for whether…  x is greater than 0 and y is less than 5  x is greater than zero or y is equal to z  it’s not the case that x is greater than the product of y and z Exam tip! “whether”  boolean Exam tip! “whether”  boolean

9. … boolean variables  Break complex expressions down boolean failedMidterm = (midtermGrade < 50); boolean failedFinal = (finalGrade < 50); boolean failedBothTests = failedMidterm && failedFinal;  String comparisons (all return boolean values)  oneString.equals(anotherString)  oneString.equalsIgnoreCase(anotherString)  oneString.startsWith(anotherString)  oneString.endsWith(anotherString) Exam tip! boolean a = true, b = false, c = false; !a a && b (a || c) && (!b && !c) (a && !b) || c Exam tip! boolean a = true, b = false, c = false; !a a && b (a || c) && (!b && !c) (a && !b) || c

10. Loops  for and while loops  Convert between them  Loop structure  Initialize, test/condition, update, process for (initialize; test; update) { process; } initialize; while (test) { process; update; } Exam tip! When asked for an algorithm, make sure to include all these 4 steps! Exam tip! When asked for an algorithm, make sure to include all these 4 steps!

11. … Loops  Write loops to:  Calculate sum, average, max, min, of numbers  When to stop? »Negative number »Yes/no  Track the variable’s values: a = 1; a++; b = a + 6; b--; c = b * 5; c += a; a *= 10; b /= 2; c %= 4; a *= b + c; Exam tip! Write the loops for these with or without arrays! Exam tip! Write the loops for these with or without arrays!

12. Named Constants  public static final data-type CONST_NAME = value  Naming conventions  variableName  CONSTANT_NAME

13. Nested structures  Loops with Conditionals while (num >= 0) { // say whether num is divisible by 5 // say whether num is divisible by 5 if (num % 5 == 0) { if (num % 5 == 0) { System.out.println(num + “ is divisible by 5.”); System.out.println(num + “ is divisible by 5.”); } else { } else { System.out.println(num + “ is not divisible by 5.”); System.out.println(num + “ is not divisible by 5.”); } // get next number // get next number num = kbd.nextInt(); num = kbd.nextInt();}

14. … Nested structures  if inside if: System.out.println(“A”); if (condition1) { System.out.println(“B”); System.out.println(“B”); if (condition2) { if (condition2) { System.out.println(“C”); System.out.println(“C”); }} possible output: A AB ABC pattern: always A sometimes B when B, sometimes C

15. … Nested structures  Rewrite sequential-if to cascading-if if (age < 18) { System.out.print(“Child”); } if (age >= 18 && age < 65) { System.out.print(“Adult”); } if (age >= 65) { System.out.print(“Senior”); } if (age < 18) { System.out.print(“Child”); } else if (age < 65) { System.out.print(“Adult”); } else { System.out.print(“Senior”) ; }

16. … Nested structures  Loops inside loops:  Review A05  Draw a rectangle: »Get w and h from user  Draw a tree: »Given the base size Exam tip! A05 Solution is posted! Check it out! Exam tip! A05 Solution is posted! Check it out!

17. Scopes of a variable/parameter  Inside loops  Inside if-else  Inside method (variables and parameters)  Inside class (instance and class variables)

18. Methods Exam tip! str.equals(), str.startsWith(), str.toUpperCase() kbd.next(), kbd.nextLine(), etc Exam tip! str.equals(), str.startsWith(), str.toUpperCase() kbd.next(), kbd.nextLine(), etc

19. … Methods  For reading data (kbd is a Scanner)  kbd.nextInt() kbd.nextDouble() kbd.next() kbd.nextLine()  For checking strings (resp is a String)  resp.equals(“yes”) resp.equalsIgnoreCase(“yes”) resp.startsWith(“y”) resp.toLowerCase()

20. Arguments  “Arguments” are given to the method »we also say that the method takes arguments  Math.sqrt(10) – 10 is the (only) argument »asks Math for the square root of 10  Math.pow(5, 2) – 5 and 2 are both arguments »asks Math for 5 to the power 2 (i.e. 5 2 )  arguments must be in the right order! »Math.pow(2, 5) is 2 5, not 5 2

21. Argument Types  Arguments must be the right type!  Math.pow(“fred”, true) makes no sense! »the two arguments must be numbers »doubles are OK: Math.pow(3.7, 1.98)  resp.startsWith(7) makes no sense! »the argument must be a String: resp.startsWith(“7”)  And in the right order  and there must be the right number of them! »Math.pow(5) and Math.pow(1, 2, 3) make no sense!

22. Exercise  Assume the calls below are correct. What argument type(s) does each method take?  Math.getExponent(3400.2)  Math.ulp(2.6)  Math.scalb(4.5, 2)  str.split(“:”, “one:two:three:four”)  str.length()  str.regionMatches(true, 0, “this”, 7, 50)

23. Return Types  Methods can return any kind of value »(or even none)  Math.sqrt(10) returns a double value  Math.max(3, 5) returns an int value  kbd.nextInt() returns an int value  kbd.next() returns a String value  str.toUpperCase() returns a String value  str.indexOf(“n”) returns an int value

24. Exercise  Assuming the code below is correct, what kind of value does each method return? double x, y = 3.2; int n = 42; String name = “Mark”; boolean good; name = name.replaceFirst(“a”, “o”); x = Math.exp(y); n = Math.getExponent(x); good = (name.equalsIgnoreCase(“mork”));

25. Exercise  Void or value-returning?  & what kind of value does each VRM return? if (answer.startsWith(“Y”)) { double x = Math.pow(3, 6); double x = Math.pow(3, 6); int n = kbd.nextInt(); int n = kbd.nextInt(); System.out.println(“Hello!”); System.out.println(“Hello!”); myWin.setVisible(true); myWin.setVisible(true); double cm = Converter.cmFromFeetInches(n, x); double cm = Converter.cmFromFeetInches(n, x); thingamajig.doStuff(cm, x, that.get(n)); thingamajig.doStuff(cm, x, that.get(n));} Note: there are two method calls on the last line. How can we find out what kind of value get returns?

26. Method declaration  Header: 1.public/private 2.static (or non-static) 3.return-type (void, int, double, String, boolean, Class, etc) 4.methodName 5.(paramType1 param1, paramType2 param2, …)  E.g.) »public static double fahrenheitFromCelsius(double degC) »public boolean equalsTo(int a[], int b[]) »private int[] subtract(int a[], int b[]) Exam tip! Write a method that takes and returns Takes  parameters Returns  return type Exam tip! Write a method that takes and returns Takes  parameters Returns  return type

27. Arguments and Parameters  Arguments are values (10, 15.4, “Hello”)  Parameters are variables  need to be declared like variables »(double degC), (int ft, double in)  only differences are: »declarations are separated by commas, not ;s »every parameter needs its own type, even if they’re all the same type: (double x, double y, double z), (int a, int b)(double x, double y, double z), (int a, int b) Exam tip! Given a list of parameters, a method call needs to have corresponding argument list! Exam tip! Given a list of parameters, a method call needs to have corresponding argument list!

28. Method Body  The method body is where you tell the computer how to compute the value needed »how to convert feet and inches to cm »how to convert Celsius to Fahrenheit »...  Need to know how to do it... »feet times 12 plus inches, all multiplied by 2.54 ...and translate it into Java: result = (ft * 12 + in) * 2.54;

29. … Method Body  Anything you can do in main …  …you can do in a method  (local) variable declarations (including objects)  assignment statements  selection controls (if, if-else, if-else-if)  repetition controls (while, for)  method calls  (other things we haven’t learned about yet) Exam tip! Did you see the related question in midterm? Exam tip! Did you see the related question in midterm?

30. Method “Stubs”  Our methods need return commands  need to return the right kind of thing  we want to return exactly the right value  but Java doesn’t care!  So we can just put a “dummy” return in  return something so that Java doesn’t complain  worry about making it right later  we call such a function a “stub” (it’s short) Exam tip! As long as your methods compile with proper parameter lists and return types, your stubs are good enough (for this course)! Exam tip! As long as your methods compile with proper parameter lists and return types, your stubs are good enough (for this course)!

31. Converter Class with Stubs public class Converter { public static double fahrenheitFromCelsius(double degC) { public static double fahrenheitFromCelsius(double degC) { return 0.0; return 0.0; } public static double cmFromFeetInches(int ft, double in) { public static double cmFromFeetInches(int ft, double in) { double result = 0.0; double result = 0.0; return result; return result; }}  return statement is the last line of a method!

32. Naming Methods  Method names in mixed case  capital letter for 2 nd and subsequent words  The same as variable’s naming convention

33. Putting them together public static returnType methodName(pType1 p1, pType2 p2) { body... body... return result; return result;}  returnType, pType1 and pType2 are int, or double, or String, or Class, or an array, or any data type we’ve seen!  methodName is the name of the method  p1 and p2 are the parameters  body is for the commands calculating the result  static is only needed for class (static) methods

34. Classes vs. Objects  Classes can be used right away Utilities.printTitle(“Utilities Demo”); »so long as we can “see” them  Objects need to be created »except for Strings, which are so massively useful… Scanner kbd = new Scanner(System.in);  objects contain data  different objects have different data  methods are mostly about that data Exam tip! static methods! Exam tip! static methods!

35. Declaring Objects  Most Java objects created using new »usually with arguments »arguments depend on the class kbd = new Scanner(System.in); rover = new Animal(Animal.DOG);// I made this up! c1 = new Color(255, 127, 0);// This is orange okButton = new JButton(“OK”); »not Strings, tho’ s1 = “Strings are special!”; s2 = new String(“But this works, too!”); Remember to import java.awt.Color; import javax.swing.JButton;

36. Student Class (Start) public class Student { private String aNumber;// A00... private String name;// family name, givens private int pctGrade;// 0..100 …} Exam tip! instance variables are declared private (not public) no “static”; no “final”! Exam tip! instance variables are declared private (not public) no “static”; no “final”!

37. Java modifiers  Access modifiers  public  private  Non-access modifiers  static  final

38. Which modifiers?  Instance variables  private dataType  Class variables  private static dataType  Instance constant  public final dataType  Class constant  public static final dataType Exam tip! Class  static Constant  final Exam tip! Class  static Constant  final

39. Constructors  Constructor “builds” the object  gives a value to each of the instance variables private String aNumber;// A00… private String aNumber;// A00… private String name;// Last, First private String name;// Last, First private int grade;// 0.. 100 private int grade;// 0.. 100 public Student(String a, String n, int g) { public Student(String a, String n, int g) { aNumber = a; aNumber = a; name = n; name = n; grade = g; grade = g; } a, n, and g are the parameters: the values the caller wants to use; aNumber, name, and grade are the instance variables: the values we will use.

40. … Constructors  Generally declared public  anyone can build a Scanner, a Student, …  Name is exactly the same as the class name  class Student  constructor named “Student”  class Animal  constructor named “Animal”  No return type  not even void!  Argument for each instance variable (often)

41. … Constructors  Their job is to give a value to each instance variable in the class  and so often just a list of assignment commands »instanceVariable = parameter; aNumber = a; name = n; grade = g;  But may want to check if values make sense  so maybe a list of if-else controls

42. Checking Values  If given value makes no sense, use a default »but still instanceVariable = (something); public Student(String a, String n, int g) { if (a.startsWith(“A”) && a.length() == 9) { if (a.startsWith(“A”) && a.length() == 9) { aNumber = a; aNumber = a; } else { } else { aNumber = “(illegal)”; aNumber = “(illegal)”; } name = n; name = n; …} Exam tip! Given object instantiation, write a constructor! int r, g, b; r = g = b = 0; Colour col = new Colour(r,g,b); Set values of r, g, b if between [0,255] Otherwise zero Exam tip! Given object instantiation, write a constructor! int r, g, b; r = g = b = 0; Colour col = new Colour(r,g,b); Set values of r, g, b if between [0,255] Otherwise zero

43. Create a Student object Student stu = new Student(“A00000000”, “Dent, Stu”, 100);  The argument list should match the parameter list of the constructor  (String a, String n, int g)  The same as any other method calls public static boolean equalsTo(int a[], int b[]) int[] a = new int[len]; int[] b = new int[len]; if (ArrayOperations.equalsTo(a, b)) {}

44. Getters and Setters  Getters: public String getANumber() { return aNumber; return aNumber;}  Setters: public void setPctGrade(int newGrade) { if (0 <= grade && grade <= 100) { if (0 <= grade && grade <= 100) { pctGrade = newGrade; pctGrade = newGrade; }} Exam tip! Getters: public! Anyone can ask! Return type! Never void! Non-static! Each student has own name! Just return the instance variable! Exam tip! Getters: public! Anyone can ask! Return type! Never void! Non-static! Each student has own name! Just return the instance variable! Exam tip! Setters: public! Anyone can change! Return type! (usually) void! Non-static! Each student has own grade! Set the value (with some conditions) Exam tip! Setters: public! Anyone can change! Return type! (usually) void! Non-static! Each student has own grade! Set the value (with some conditions)

45. this keyword  Text definition: “Within a method definition, you can use the keyword this as a name for the object receiving the method call.”

46. … this keyword public class SomeClass { private int var; public SomeClass(){ this.var = 0;//instance variable var = 0;//instance variable } public void incrementVar(int var){ this.var++;//instance variable var++;//local parameter!!! } public void printVar(){ System.out.println(this.var);//instance variable System.out.println(var);//instance variable }} Exam tip! this is only needed to disambiguate things. Exam tip! this is only needed to disambiguate things.

47. Instance (non-static) and class (static)  Instance variables/methods  Belongs to a particular object  Each instance/object of the class has its own value  IM uses object’s values (IV)  Class (static) variables/methods  Belongs to a particular class  All the instances/objects of the class point to the same CV (hence, the same value)  CM uses CV (static) values

48. final and Non-final  final means once it’s assigned a value, you cannot change it (immutable)!  Can be static and final (class constant)  Or non-static and final (instance constant)

49. Class (static) Variables public class Student { public final String A_NUMBER; private String name; private int pctGrade; private static int nextANumber = 1;  nextANumber belongs to Student class  not to each Student, but to every Student

50. Assigning Student Numbers  To create a student:  assign the next available number  update the next available number  (continue setting other IVs) public Student(String n, int g) { A_NUMBER = String.format(“A%08d”, nextANumber); ++nextANumber;…} String.format is like System.out.printf, BUT it makes the String, it doesn’t print it

51. … Assigning Student Numbers Student s1, s2; Student s1, s2; s1 = new Student("Akiyama, Yasushi",75); s1 = new Student("Akiyama, Yasushi",75); s2 = new Student("Cooper, Ray",90); s2 = new Student("Cooper, Ray",90); System.out.println(s1.A_NUMBER); System.out.println(s1.A_NUMBER); System.out.println(s2.A_NUMBER); System.out.println(s2.A_NUMBER); Output: A00000001 A00000002

52. Car class public class Car { public final String VIN; private static int numCars = 0; //other constants and variables public Car(double tankSize, double fuelConsumption) { this.numCars++; VIN = String.format("CSCI1226%04d", this.numCars); //other operations }

53. … Car class // create a few cars Car car1 = new Car(45.0, 7.5); Car car2 = new Car(45.0, 6.8); Car car3 = new Car(40.0, 6.2); System.out.println(car3.VIN); Output: CSCI12260003

54. toString() method @Override public String toString() { return name + “ (” + A_NUMBER + “)” return name + “ (” + A_NUMBER + “)”} Call it explicitly: Student s = new Student(“Pat”, 80); System.out.println(s.toString()); Or implicitly: Student s = new Student(“Pat”, 80); System.out.println(s) ;

55. Arrays

56. Array Base Types  Arrays can be of any base type, any size int[] score = new int[600]; double[] weight = new double[70]; boolean[] answers = new boolean[10]; String[] words = new String[5000];  …any type at all Scanner[] scanners = new Scanner[2]; Student[] myStudents = new Student[10]; The text recommends singular names. I tend to use plural. Exam tip! Make sure you know how to declare and create arrays of any data type! Exam tip! Make sure you know how to declare and create arrays of any data type!

57. Array Sizes  Remember to declare constants for numbers you use in multiple places  like in array declaration and loop! int[] nums = new int[NUM_ITEMS]; int[] nums = new int[NUM_ITEMS]; for (int i = 0; i < NUM_ITEMS; i++) for (int i = 0; i < NUM_ITEMS; i++) nums[i] = kbd.nextInt(); nums[i] = kbd.nextInt();  Makes it easy to change the number later // # elements – change to 600 when debugged! public static final int NUM_ITEMS = 6;

58. Arrays Know Their Own Length  Array length public static final int MAX_WORDS = 200; … String[] word = new String[MAX_WORDS]; String[] word = new String[MAX_WORDS]; if (word.length != MAX_WORDS) { if (word.length != MAX_WORDS) { System.err.println(“Your computer is broken!”); System.err.println(“Your computer is broken!”);} Exam tip! Don’t confuse with String’s length() method! arr.length is not a method, hence no (), and it’s final so cannot be changed! (public final field length;) Exam tip! Don’t confuse with String’s length() method! arr.length is not a method, hence no (), and it’s final so cannot be changed! (public final field length;)

59. Creating Arrays with Values  Create an array object by listing elements int[] arr = new int[]{2, 3, 5, 7, 11};  It knows its own length! for(int i = 0; i < arr.length; i++) { System.out.print(arr[i] + “ ”); }  Can change the array later arr = new int[]{13, 17, 19, 23}; 2 3 5 7 11 Initialize.java

60. Average and Differences // read and sum the numbers int[] num = new int[NUM_ITEMS]; int sum = 0; S.o.p(“Enter the ” + NUM_ITEMS + “ items below”); for (int i = 0; i < NUM_ITEMS; i++) { num[i] = kbd.nextInt();// remember the # num[i] = kbd.nextInt();// remember the # sum += num[i];// add it to sum sum += num[i];// add it to sum} // calculate the average double ave = (double)sum / (double)NUM_ITEMS; // print the difference from the average of each for (int i = 0; i < NUM_ITEMS; i++) { S.o.p((num[i] – ave)); S.o.p((num[i] – ave));} WeeklyTemps.java

61. Arrays as Parameters  Methods can have [] parameters, just declare the parameter to be an array! public static int sumArray(int[] arr)  It’s just like any other parameter  gets its value from the method call  It’s just like any other array  it knows how long it is

62. Method to Sum an Array  Array comes from caller int[] n = new int[]{2, 3, 5, 7, 11}; int addedUp = sumArray(n);  Method adds up its elements public static int sumArray(int[] arr) { int sum = 0; int sum = 0; for (int i = 0; i < arr.length; i++) { for (int i = 0; i < arr.length; i++) { sum += arr[i]; sum += arr[i]; } return sum; return sum;} ArrayMethod.java

63. Returning Arrays  Methods can return arrays  return type is an array type public int[] dice(int howMany) { … } public String[] wordsFrom(String line) { … }  Like any other object-returning method, the object/array to be returned is new int[] result = new int[howMany]; … return result; ArrayReturn.java

64. Exercise  Be able to write:   equalsTo   subtract   max   min from ArrayOperations.java

65. Final Exam (Section A)  Saturday, December 6, 2014, 7:00 pm - 10:00 pm  ME Auditorium  Hand-written test -- bring pen & whiteout or pencil & eraser.  No electronic devices allowed  You may bring a reference sheet:  A single 8.5x11 (A4) sheet of paper.  It may be hand-written or printed.  You may use both sides of the sheet.  You can prepare it alone or with friends, but bring your own copy (no sharing copies during the test).  If your sheet is too large (or otherwise breaks the rules), it will be confiscated.

66. Final Exam (Section B)  Friday, December 12, 2014, 9:00 am - 12:00 pm  Atrium 101  Hand-written test -- bring pen & whiteout or pencil & eraser.  No electronic devices allowed  You may bring a reference sheet:  A single 8.5x11 (A4) sheet of paper.  It may be hand-written or printed.  You may use both sides of the sheet.  You can prepare it alone or with friends, but bring your own copy (no sharing copies during the test).  If your sheet is too large (or otherwise breaks the rules), it will be confiscated.