1. Lecture 2 Content: Control Structures: Branching logic Control Structures: Looping logic Diagramming Reading Files from Scanner Type Conversions Promotion and Casting Random Numbers Arrays & ArrayList Driver, Bean, Utility Reference versus variable MyGregCalendar The new keyword Implicit versus explicit params Return mutable reference member cloned Static fields such as Math.PI passByVal, passByRef, swap JavaDocs

2. Control Structures See edu.uchicago.cs.java.lec02.control

3. Shorthand See blackboard

4. Arrays & ArrayLists See edu.uchicago.cs.java.lec02.arrays

5. Arrays arrays of prmitivies arrays of Objects multidimentional arrays

6. Array: Sequence of values of the same type Construct array: new double[10] Store in variable of type double[] : double[] dDatas = new double[10]; When array is created, all values are initialized depending on array type: Numbers: 0 Boolean : false Object References: null Arrays Big Java by Cay Horstmann Copyright © 2009 by John Wiley & Sons. All rights reserved.

7. Array: Sequence of values of the same type double[] dValues = {2.5, 8.1, 3.79, 0, 6.0}; The above declares and intializes an array of double[] String[] strNames = {"Harry", "Lary", "Mary", "Perry"}; The above declares and initializes an array of String[] Arrays: declare and init

8. Arrays Use [] to access an element: double[] dValues = new double[10]; dValues[2] = 29.95; Big Java by Cay Horstmann Copyright © 2009 by John Wiley & Sons. All rights reserved.

9. Using the value stored: System.out.println("The value of this data item is " + dValues[2]); //dValues[2] (a double) is promoted to a String. Get array length as dValues.length (Not a method!) Index values range from 0 to length - 1 Accessing a nonexistent element results in a bounds error: double[] values = new double[10]; values[10] = 29.95; // ERROR – out of bounds Limitation: Arrays have fixed length! Arrays Big Java by Cay Horstmann Copyright © 2009 by John Wiley & Sons. All rights reserved.

10. Declaring Arrays Big Java by Cay Horstmann Copyright © 2009 by John Wiley & Sons. All rights reserved.

11. Syntax 7.1 Arrays Big Java by Cay Horstmann Copyright © 2009 by John Wiley & Sons. All rights reserved.

12. // Don't do this int[] accountNumbers; double[] balances; Make Parallel Arrays into Arrays of Objects Big Java by Cay Horstmann Copyright © 2009 by John Wiley & Sons. All rights reserved.

13. Avoid parallel arrays by changing them into arrays of objects: BankAccount[] accounts; Make Parallel Arrays into Arrays of Objects Big Java by Cay Horstmann Copyright © 2009 by John Wiley & Sons. All rights reserved.

14. multidimensional arrays int[][] nNumbers = new int[3][4]; boolean[][] bExams = { new boolean[6], new boolean[9], new boolean[3], new boolean[8] }; //ragged array

15. Array Lists ArrayList class manages a sequence of objects Can grow and shrink as needed (it's a Vector) ArrayList class supplies methods for many common tasks, such as inserting and removing elements ArrayList is a generic class: ArrayList collects objects of type parameter T : ArrayList strNames = new ArrayList (); strNames.add("Emily"); strNames.add("Bob"); strNames.add("Cindy"); size method yields number of elements Big Java by Cay Horstmann Copyright © 2009 by John Wiley & Sons. All rights reserved.

16. To add an object to the end of the array list, use the add method: names.add("Emily"); names.add("Bob"); names.add("Cindy"); Adding Elements Big Java by Cay Horstmann Copyright © 2009 by John Wiley & Sons. All rights reserved.

17. To obtain the value an element at an index, use the get method Index starts at 0 String strName = strNames.get(2); // gets the third element of the array list Bounds error if index is out of range Most common bounds error: int n = strNames.size(); strName = strNames.get(n); // Error // legal index values are 0... n-1 Retrieving Array List Elements Big Java by Cay Horstmann Copyright © 2009 by John Wiley & Sons. All rights reserved.

18. To set an element to a new value, use the set method: strNames.set(2, " Carolyn " ); Setting Elements Big Java by Cay Horstmann Copyright © 2009 by John Wiley & Sons. All rights reserved.

19. To remove an element at an index, use the remove method: strNames.remove(1); Removing Elements Big Java by Cay Horstmann Copyright © 2009 by John Wiley & Sons. All rights reserved.

20. strNames.add("Emily"); strNames.add("Bob"); strNames.add("Cindy"); strNames.set(2, "Carolyn"); strNames.add(1, "Ann"); strNames.remove(1); Adding and Removing Elements Big Java by Cay Horstmann Copyright © 2009 by John Wiley & Sons. All rights reserved.

21. Syntax 7.2 Array Lists Big Java by Cay Horstmann Copyright © 2009 by John Wiley & Sons. All rights reserved.

22. Promotion and Casting See edu.uchicago.cs.java.lec02.cast

23. Promotion & Casting Automatic promotion; this occurs when one operand is of lesser precision than the other and completing the operation will not reduce precision of result. double dResult = nNumerator / dDenominator; In the above case, nNumerator is promoted to a double. int nResult = (int)(nNumerator / dDenominator); you must CAST because you can't assign the return value, intially a double (64 bit flotating precision) to an int (32 bit int precision)

24. Big Java by Cay Horstmann Copyright © 2009 by John Wiley & Sons. All rights reserved. Cast converts a value to a different type: double dBalance = dTotal + dTax; //dBalance == 10.89 int nDollars = (int) dBalance; //nDollars == 10 Math.round converts a floating-point number to nearest integer: long lRounded = Math.round(dBalance); // if dBalance is 13.75, then lRounded is set to 14 Cast and Round

25. Big Java by Cay Horstmann Copyright © 2009 by John Wiley & Sons. All rights reserved. Syntax 4.2 Cast

26. Type Conversion Each Wrapper class has some parse functions. Integer.parseInt(String str); Double.parseDouble(String str); Byte.parseByte(String str); Boolean.parseBoolean(String str); etc.

27. The New Keyword See edu.uchicago.cs.java.lec02.newkeyword

28. Using the new Keyword Unless you use the ‘new’ keyword, nothing has been instantiated and the object does NOT exist in memory. (the exception is static) Driver/Bean/Utility

29. Big Java by Cay Horstmann Copyright © 2009 by John Wiley & Sons. All rights reserved. Example: public class Financial { public static double percentOf(double dP, double dA) { return (dP / 100) * dA; } // More financial methods can be added here. } Call with class name instead of object: double dTax = Financial.percentOf(dTaxRate, dTotal); Static Methods

30. Big Java by Cay Horstmann Copyright © 2009 by John Wiley & Sons. All rights reserved. Here is another example: public class Geometry { public static double area(Rectangle rec) { return rec.getWidth() * rec.getHeight(); } // More geometry methods can be added here. } Static Methods

31. Implicit versus Explicit Parameters The implicit parameter is the object reference, whereas the explicit parameter(s) are/is the argument(s) to the method. strName.indexOf(cSpace); Math.pow(2,3); //no implicit param -- static Most often, when we refer to parameters, we mean the explicit parameters.

32. Big Java by Cay Horstmann Copyright © 2009 by John Wiley & Sons. All rights reserved. A static method does not operate on an object double dY = mthObject.sqrt(); // Error double dY = Math.sqrt(9); //correct Naming convention: Classes start with an uppercase letter; objects start with a lowercase letter: Sometimes you will find nonstatic implementations in Java that would seem like perfect candidates for static, such as Random. Random rnd = new Random(); rnd.nextInt(10); //correct Random.nextInt(10); //incorrect Calling Static Methods

33. Suppose Java had no static methods. How would you use the Math.sqrt method for computing the square root of a number nX? Answer: Math mat = new Math(); double dResult = mth.sqrt(nX); Self Check 8.12 Big Java by Cay Horstmann Copyright © 2009 by John Wiley & Sons. All rights reserved.

34. Big Java by Cay Horstmann Copyright © 2009 by John Wiley & Sons. All rights reserved. Syntax 4.3 Static Method Call

35. Big Java by Cay Horstmann Copyright © 2009 by John Wiley & Sons. All rights reserved. A static variable belongs to the class, not to any object of the class: public class BankAccount {... private double dBalance; private int nAccountNumber; private static int nLastAssignedNumber = 1000; } If nLastAssignedNumber was not static, each instance of BankAccount would have its own value of nLastAssignedNumber Static Variables

36. Big Java by Cay Horstmann Copyright © 2009 by John Wiley & Sons. All rights reserved. Static constants, which may be either private or public: public class BankAccount {... public static final double OVERDRAFT_FEE = 5; // Refer to it as BankAccount.OVERDRAFT_FEE } //in the above case, OVERDRAFT_FEE is a constant Static Variables

37. Big Java by Cay Horstmann Copyright © 2009 by John Wiley & Sons. All rights reserved. Syntax 4.1 Constant Definition

38. Big Java by Cay Horstmann Copyright © 2009 by John Wiley & Sons. All rights reserved. A final variable is a constant Once its value has been set, it cannot be changed Named constants make programs easier to read and maintain Convention: Use all-uppercase names for constants final double QUARTER_VALUE = 0.25; final double DIME_VALUE = 0.1; final double NICKEL_VALUE = 0.05; final double PENNY_VALUE = 0.01; dPayment = nDollars + nQuarters * QUARTER_VALUE + nDimes * DIME_VALUE + nNickels * NICKEL_VALUE + nPennies * PENNY_VALUE; Constants: final

39. Harry tells you that he has found a great way to avoid those pesky objects: Put all code into a single class and declare all methods and variables static. Then main can call the other static methods, and all of them can access the static variables. Will Harry’s plan work? Is it a good idea? Answer: Yes, it works. Static methods can access static variables of the same class. But it is a terrible idea. As your programming tasks get more complex, you will want to use objects and classes to organize your programs. Self Check 8.15 - funny Big Java by Cay Horstmann Copyright © 2009 by John Wiley & Sons. All rights reserved.

40. Strings

41. Useful methods of String char charAt(int index) int compareTo(String anotherString) boolean endsWith(String suffix) int indexOf(multiple) int length() String substring(int begin, int end) String trim()

42. Big Java by Cay Horstmann Copyright © 2009 by John Wiley & Sons. All rights reserved. Immutable class: Has no mutator methods (e.g., String ): String strName = "John Q. Public"; String strUppercased = strName.toUpperCase(); // strName is not changed It is safe to give out references to objects of immutable classes; no code can modify the object at an unexpected time. The implicit paramater is immutable! String is Immutable

43. String Pools To optimize performance, the JVM may keep a String in a pool for reuse. Sometimes is does and sometimes it doesn't. Very unpredictable. This means that in some VMs (or even the same VM at different times), two or more object references may be pointing to the same String in memory. However, since you can not rely upon pooling, you MUST assume that each string has its own object reference. Besides, since Strings are immutable, you need not consider the consequences of passing a reference.

44. Big Java by Cay Horstmann Copyright © 2009 by John Wiley & Sons. All rights reserved. A string is a sequence of characters Strings are objects of the String class A string literal is a sequence of characters enclosed in double quotation marks: "Hello, World!" String length is the number of characters in the String Example: "Harry".length() is 5 Empty string: "" Although we use the shortcut: String strName = “Robert”; we are actually doing this: String strName = new String(“Robert”); The String Class

45. Big Java by Cay Horstmann Copyright © 2009 by John Wiley & Sons. All rights reserved. Use the + operator: String strName = "Dave"; String strMessage = "Hello, " + strName; // strMessage is "Hello, Dave" If one of the arguments of the + operator is a string, the other is converted to a string String strA = "Agent”; int n = 7; String strBond = strA + n; // strBond is "Agent7" Concatenation

46. Big Java by Cay Horstmann Copyright © 2009 by John Wiley & Sons. All rights reserved. String str2 = strGreeting.substring(7, 12); // str2 is "World" Substring starts at the begin-index and ends at end-index - 1 Substrings

47. Escape Sequences to include the quotes in a string, use the escape sequences: strOne = "\"Quotation\""; to print \\ StrBackSlashes = "\\\\"; Unicode values http://oreilly.com/actionscript/excerpts/as3- cookbook/appendix.html

48. Escape Sequences Escape Sequenc e Character \nnewline \ttab \bbackspace \fform feed \rreturn \"" (double quote) \'' (single quote) \\\ (back slash) \uDDDD character from the Unicode character set (DDDD is four hex digits)

49. Keyboard Input edu.uchicago.cs.java.lec02.scanner

50. Keyboard Input Scanner -- or you can define your own Scanner scn = new Scanner(System.in); Scanner scn = new Scanner(File filSource); throws FileNotFoundException strInput = scn.nextLine();

51. Big Java by Cay Horstmann Copyright © 2009 by John Wiley & Sons. All rights reserved. System.in has minimal set of features — it can only read one byte at a time In Java 5.0, Scanner class was added to read keyboard input in a convenient manner Scanner scn = new Scanner(System.in); System.out.print("Enter quantity:"); int nQuantity = scn.nextInt(); nextDouble reads a double nextLine reads a line (until user hits Enter) next reads a word (until any white space) Reading Input

52. Random See edu.uchicago.cs.java.lec02.random

53. Random numbers import java.util.Random; int n = rnd.nextInt(); double d = rnd.nextDouble(); int n = rnd.nextInt(int nNum); rnd.nextInt(20); //0-19 //in this above case 20 is multipled by some real number between 0 and 1 exclusive; then converted to int; it will return 0 to 19.

54. Pass by value and reference See edu.uchicago.cs.java.lec02.passby

55. pass by value pass by reference Action: Tell my accountant how much I intend to spend on a new car. Change in bank account: no change. Action: Swipe debit card and enter pin at the Bently dealership. Change in bank account: -125k.

56. Primitives versus Objects memory PrimitivesObjects Variables store values and are allocated memory depending on their type. How much?...refer to Java Primitives slide. References store memory addresses. The size of the allocation for the object reference is VM specific, but is usually the native pointer size; 32bits in 32-bit VM, and 64bits in a 64-bit VM. Garbage collected when out-of-scope. Passed into methods by valuePassed into methods by reference

57. Objects See edu.uchicago.cs.java.lec02.console21

58. Class Object A blueprint is to a house as a class is to an object Class = Blueprint

59. Class Objects

60. Class Object A blueprint is to a car as a class is to an object Class = Blueprint

61. Class Objects

62. Spot the “class” here

63. Constructors Has the same name and as the class (very important - otherwise not a constructor) The ONLY method that is allowed to be capitalized; and must be capitalized. If you don't define a constructor, a default no- arg constructor is implied that will set fields to zero, or null. If you define any constructor, then the default constructor is not available to you.

64. Using anonymous objects Anonymous objects are useful for "hard- coding" objects and passing them into Constructors. The enclosing class will contain a reference to this object, so we can find it later.

65. Review of Eclipse

66. Important shortcuts in Eclispe Ctrl-space – materialize template code “.” - when used on a class or object reference, this pulls up code-complete. Alt-shift-r – used to rename variable-names globally throughout the application Ctrl-shift-f – Format Refactor || Extract method() / Convert Local Variable to Field Source || Generate Window || Preferences || Java || Code Style || Formatter || Edit || On/Off Tags //@formatter:off //####################### PSEUDOCODE ######################### ${cursor} //############################################################ //@formatter:on Window || Preferences || Java || Code Style || Fields || Edit List: b,y,s,c,n,l,d,f,str

67. Console21

68. One player and one dealer play against one another in a game of 21. A player starts with some money (100 dollars) and bets 10 dollars each hand. The game is played with a 52-card chute. The game ends when the player decides to quit. Game-play starts with the player introducing himself by name, and the dealer dealing himself and the player two cards each. After the intial deal If the dealer and the player both have blackjack, then push, ask to play again. If the dealer has blackjack then the player loses his 10 dollars, ask to play again. If the player has blackjack, then the player wins 15 dollars, ask to play again If neither dealer nor player have blackjack, then the player has the option to either hit (so long as the total value of his hand is less than or equal to 21) or stick. If the player busts when hitting, then the player loses his 10 dollars, and is asked to play again. If the player does not bust, then the dealer is obliged to hit while his total is less than 17. If the dealer busts, then the player wins $10, and is asked to play again. If neither dealer nor player busts, then a tie will push. If the player has the highest hand, then the player wins $10, and is asked to play again. If the dealer has the highest hand, then the player loses $10, and is asked to play again. Once the hand is over, both players return their cards, and those cards are put-back onto the top of the chute. The chute is shuffled once 52 cards have been dealt.

69. Packages

70. Packages help organize your code Packages disambiguate Packages avoid naming conflicts Using the fully qualified name of an object, you need not import it (though it's best to import).

71. Big Java by Cay Horstmann Copyright © 2009 by John Wiley & Sons. All rights reserved. Package: a collection of classes with a related purpose Import library classes by specifying the package and class name: import java.awt.Rectangle; You don’t need to import classes in the java.lang package such as String and System Packages

72. Big Java by Cay Horstmann Copyright © 2009 by John Wiley & Sons. All rights reserved. Syntax 2.4 Importing a Class from a Package

73. Big Java by Cay Horstmann Copyright © 2009 by John Wiley & Sons. All rights reserved. PackagePurposeSample Class java.lang Language support Math java.util Utilities Random java.io Input and output PrintStream java.awt Abstract Windowing Toolkit Color java.applet Applets Applet java.net Networking Socket java.sql Database Access ResultSet javax.swing Swing user interface JButton omg.w3c.dom Document Object Model for XML documents Document Packages Package: Set of related classes Important packages in the Java library:

74. Big Java by Cay Horstmann Copyright © 2009 by John Wiley & Sons. All rights reserved. To put classes in a package, you must place a line package packageName ; as the first instruction in the source file containing the classes Package name consists of one or more identifiers separated by periods Organizing Related Classes into Packages

75. Big Java by Cay Horstmann Copyright © 2009 by John Wiley & Sons. All rights reserved. For example, to put the Financial class introduced into a package named com.horstmann.bigjava, the Financial.java file must start as follows: package com.horstmann.bigjava; public class Financial {... } Default package has no name, no package statement Organizing Related Classes into Packages

76. Big Java by Cay Horstmann Copyright © 2009 by John Wiley & Sons. All rights reserved. Can always use class without importing: java.util.Scanner in = new java.util.Scanner(System.in); Tedious to use fully qualified name Import lets you use shorter class name: import java.util.Scanner;... Scanner in = new Scanner(System.in) Can import all classes in a package: import java.util.*; Never need to import java.lang You don’t need to import other classes in the same package Importing Packages

77. Big Java by Cay Horstmann Copyright © 2009 by John Wiley & Sons. All rights reserved. Use packages to avoid name clashes java.util.Timer vs. javax.swing.Timer Package names should be unambiguous Recommendation: start with reversed domain name: com.horstmann.bigjava edu.sjsu.cs.walters : for Britney Walters’ classes ( walters@cs.sjsu.edu ) Path name should match package name: com/horstmann/bigjava/Financial.java Package Names

78. Big Java by Cay Horstmann Copyright © 2009 by John Wiley & Sons. All rights reserved. Base directory: holds your program's Files Path name, relative to base directory, must match package name: com/horstmann/bigjava/Financial.java Package and Source Files

79. Which of the following are packages? a. java b. java.lang c. java.util d. java.lang.Math Answer: a.No b.Yes c.Yes d.No Self Check 8.18 Big Java by Cay Horstmann Copyright © 2009 by John Wiley & Sons. All rights reserved.

80. Java Doc Generate default JavaDocs. Using decorations/tags. Project || Generate JavaDoc. – In Eclipse; navigate to JDK\bin\javadoc.exe to configure. Scope; public to private methods Use F1 to pull up your javadocs.

81. Is a Java program without import statements limited to using the default and java.lang packages? Answer: No — you simply use fully qualified names for all other classes, such as java.util.Random and java.awt.Rectangle. Self Check 8.19 Big Java by Cay Horstmann Copyright © 2009 by John Wiley & Sons. All rights reserved.

82. Gregorian Calendar Example

83. Asciify Example (if we have time)

84. Adding examples code to javadocs /** * * @param perSoldiers ArrayList * @return Person object * * Example: * perSenior = getMostSenior(perVets); //will return a reference to Person * */ Use the code here tages in javadocs before the methods Good idea!

85. Object Composition Objects are composed of instance fields Instance fields can be primitives or other objects //fields of this class private String strFirstName; private String strLastName; private byte yAge; //-128 to 127 private boolean bVeteran; private String strSocialSecurityNum; private ArrayList perDependents;

86. Imports and the Java API Determine the version of Java you’re using. From the cmd line> java –version http://download.oracle.com/javase/6/docs/api/ java.lang.* is automatically imported. This default behavior is know as ‘convention over configuration’. So Eclipse is very good about importing packages and catching compile-time errors. To use the javadoc for the core Java API; F1 – JDK\src.zip To see source code; F3