Summer 2007CISC121 - Prof. McLeod1 CISC121 to: “Introduction to Computing Science I” Prof. McLeod GOO550 TA’s are Ana and Krista. Web site:

Summer 2007CISC121 - Prof. McLeod2 Administration… Please give me your name, SN, QLink ID and preferred address (if not QLink). While Ana and Krista are here – we should discuss the use of the lab (GOO 458 – right across from the elevator and stairs in Goodwin Hall) and tutorials/tutoring. And: I would also like to find out what kind of programming experience you have.

Summer 2007CISC121 - Prof. McLeod3 Course Content This is not a “Java Course”! But, we need a language to demonstrate and practice the concepts to be discussed. Java is the language of choice. –A modern, platform-independent, Object-Oriented language. –We could have used many other languages equally well: C#, C++, VB, Delphi, Pascal, Turing, etc.

Summer 2007CISC121 - Prof. McLeod4 Course Content, Cont. First, a review of the Java language, then: Practical TopicsTheory TopicsAlgorithm Topics Coding Style Analysis of Complexity Data Structures Documentation Numerical Storage & Computation Recursion Testing & Debugging Sorting Assertions & Invariants Searching

Summer 2007CISC121 - Prof. McLeod5 Course Content, Cont. These topics are not Language-Dependant! Practical TopicsTheory TopicsAlgorithm Topics Coding Style Analysis of Complexity Data Structures Documentation Numerical Storage & Computation Recursion Testing & Debugging Sorting Assertions & Invariants Searching

Summer 2007CISC121 - Prof. McLeod6 Course Content, Cont. There is no single optimum way to navigate these topics: From example programs in class: –See examples (I hope!) of good coding style. –See examples of testing & debugging (I’m sure!). –Measure time of execution to verify complexity analyses. –Test the effect of finite memory used to store numbers. –Code and demonstrate the data structures and algorithms discussed.

Summer 2007CISC121 - Prof. McLeod7 Course Content, Cont. Assignments and exercises will: –At first, be used to practice fundamental Java language concepts. –Later, to explore concepts introduced in lecture. –And then to apply some of the algorithms learned to practical situations. There is a set of exercises posted and an assignment due next week – we’ll have a look shortly when we check out the course web site.

Summer 2007CISC121 - Prof. McLeod8 Course Content, Cont. Lectures will be shared with many examples and class problems (as well as “breaks” in the sunshine and/or Tim Hortons!). Some notes (the really boring ones…) may be assigned as “reading”, and will not be presented in class. Your questions are very important!! They will really help to make the lectures more interesting!

Summer 2007CISC121 - Prof. McLeod9 How to Pass Evaluation: –25% Assignments (5% each?) –25% Midterm –50% Final Exam The midterm date could be July 24 or 26 instead of a lecture (date is negotiable!). The Final Exam date (not set by me) is Aug. 15. Let me know if you anticipate having problems making any of these dates.

Summer 2007CISC121 - Prof. McLeod10 How to Pass – Cont. Do all the assignments and all practice questions yourself. Do not look at solutions until you have tried them. Ask if you have questions: –Ask Ana or Krista – in lab, by . –Ask me – during lecture, by , after lectures. Read lecture notes. Many other resources are listed on the web site. Textbook – up to you!

Summer 2007CISC121 - Prof. McLeod11 Resources Web site: – –Assignments, assignment solutions, lecture notes, reading notes, exercises, course topics and references are available from the web site. –Me: –Ana: –Krista: –Make sure I have your correct address! Some important notices will be sent out by .

Summer 2007CISC121 - Prof. McLeod12 Assignments One, possibly two(!) per week. Individual submission only – no group assignments. Submit code only (*.java file(s)) through course WebCT site. Instructions on course web site. Ana or Krista will be grading them, not me! Assignment 1 is posted.

Summer 2007CISC121 - Prof. McLeod13 Exercise Problems Are linked off the web site. You don’t hand them in. Exercise 1 is very straightforward – you can start it after you have your Java environment of choice installed.

Summer 2007CISC121 - Prof. McLeod14 Exams Yuk! Midterm July 24 or 26 – 2 hours. Final August 15 – 3 hours. Both exams are written on paper with no aids except for a supplied aid sheet (Java syntax summary).

Summer 2007CISC121 - Prof. McLeod15 Warning! Most of the contents of a first year programming course like APSC142 or CISC101 will be reviewed in two or three lectures. If you do not have any programming background nor a strong aptitude for coding, you might have problems keeping up! If you need more time with basic Java, pick up a first year-level textbook (from me or the library) and/or see if you can spend more time with Ana or Krista.

Summer 2007CISC121 - Prof. McLeod16 Java “6.0” Also called JDK The Java language has recently undergone some very positive changes (especially since 5.0). Only recently have the development tools caught up with this new release of Java. The lab machines may not yet use this new version of Java, but you might wish to use it at home. See the Resources page for instructions on how to get the software tools you need.

Summer 2007CISC121 - Prof. McLeod17 Today (Is it break time yet??) Check out the course web site. I’ll assume you have used WebCT before? Look at our first code sample to see what’s ahead! Start reviewing fundamental Java, Eclipse demo.

Summer 2007CISC121 - Prof. McLeod18 Code Sample 1 Can a computer generate random numbers? Is any part of a computer’s operation random? How does generateNums work? Why is the current time used? Which sort do you think will be faster? The longer one or the shorter one? Which one is faster? Why? Can you decide which one will be faster through analysis? Do you recognize either sorting algorithm?

Summer 2007CISC121 - Prof. McLeod19 A Simple Java Program public class HelloProg { public static void main (String [] args) { System.out.println ("Hello there!"); } // end main method } // end HelloProg class The “ // ” denotes an in-line comment. Everything else on the line is ignored by the compiler.

Summer 2007CISC121 - Prof. McLeod20 A Simple Java Program – Cont. The compiler ignores any “white space” in your source code – returns, line feeds, tabs, extra spaces and comments. Here’s our little program without white space (imagine this all on one line): public class HelloProg{public static void main(String[] args){System.out.println("Hello there!");}} This does still run, but it is hard to read…

Summer 2007CISC121 - Prof. McLeod21 Running a Java Program What happens when a program is run? Remember that Java code is platform independent. Compilation of Java source code (HelloProg.java) is done by a compiler (javac.exe) that creates a “byte code” file (HelloProg.class) that is still platform independent. This byte code file cannot be viewed or edited and is very compact.

Summer 2007CISC121 - Prof. McLeod22 Running a Java Program – Cont. Each platform capable of running Java programs has its own “JVM” or Java Virtual Machine – also called a “byte code interpreter”. This program (java.exe on a Wintel machine) runs the byte code file to perform on a specific platform.

Summer 2007CISC121 - Prof. McLeod23 Eclipse Demo Let “us” check out Eclipse and how it runs a program: –Create a project. –Create an empty program. –Edit / save / debug / run the program.

Summer 2007CISC121 - Prof. McLeod24 Running an Applet Helps to explain why Java programs run this way: An Applet is a small byte code file that is linked to a web page. Compact is important in order to minimize download times. The JVM is part of the browser, and browsers are platform specific, but the applet is not. In the case of an applet, the JVM built into the browser runs the applet.

Summer 2007CISC121 - Prof. McLeod25 A Simple Java Program – Cont. Back to our little program: public class HelloProg { public static void main (String [] args) { System.out.println ("Hello there!"); } // end main method } // end HelloProg class

Summer 2007CISC121 - Prof. McLeod26 A Simple Java Program – Cont. A Class is an “Object” in Java. All Objects in Java are Classes… A Class is a container – it holds attributes or fields (data) and methods (code that does something). Our class is called “HelloProg”. Our class must be defined in a file called “HelloProg.java”. The code “ public class HelloProg ” is used to declare the class. The contents of the class are contained in a set of curly brackets: “ { } ”.

Summer 2007CISC121 - Prof. McLeod27 A Simple Java Program – Cont. Our little class does not contain any attributes (data) and only has one method called “ main ”. The main method is declared using the code: public static void main (String [] args) As before the code is contained within: “ { } ”.

Summer 2007CISC121 - Prof. McLeod28 The main Method For the JVM to run a program, it must know where to start. By design, the starting point is always the execution of the main method. The JVM expects the main method to be declared exactly as shown – the only thing you can change is the name of the String array, called “ args ” in this little program.

Summer 2007CISC121 - Prof. McLeod29 A Simple Java Program – Cont. Our main method contains only one line of code: System.out.println ("Hello there!"); It prints out “Hello there!” to the screen (or “console”). We’ll talk more about I/O (“Input/Output”) later. Note the “ ; ” at the end of the line of code. Since the Java compiler ignores white space, it must use these characters to determine when a line finishes.

Summer 2007CISC121 - Prof. McLeod30 An Object is simply a container with a defined interface to the rest of the world. Examples: Tape Deck, Automobile, etc. An Object in Java is a class. A class contains members. Members can be attributes or fields (data) and methods. Attributes are held by instance variables defined inside the class. Object Oriented Programming in Java

Summer 2007CISC121 - Prof. McLeod31 OOP in Java - Cont. A class consists of instance variables and/or methods. By convention, instance variables are all declared before the methods: public class ShowStructure { // instance variables or “attributes” here // methods here } // end class ShowStructure

Summer 2007CISC121 - Prof. McLeod32 Program Template Class structure: public class HelloProg { public static void main (String [] args){ System.out.println ("Hello there!"); } // end main method } // end HelloProg class MethodClass

Summer 2007CISC121 - Prof. McLeod33 OOP in Java – Cont. In Java, a class is an Object, and an Object is a class (rather Zen is it not!) Code and attributes cannot be defined outside of a class. The only code that can exist outside a method are attributes.

Summer 2007CISC121 - Prof. McLeod34 Attributes Also called “class variables” or “instance variables” or “fields”. Declared within a class at the same level as the method declarations. These variables are known to all methods within a class. We will discuss them in more detail later…

Summer 2007CISC121 - Prof. McLeod35 OOP in Java - Cont. When referencing members of a class, the period operator, “. ” is used to separate member names from the class name. If members of a class are “ public ” in scope, then they can be used by other classes. If members of a class are “ private ” in scope they are only available inside the class, not outside. If the member is a method, then the method name is always followed by “ () ”, even if they are empty.

Summer 2007CISC121 - Prof. McLeod36 Modular Programs For a very short time, we will discuss programs that only have a main method. Initially we will concentrate on procedural code. Pretty soon, our main method will get too big, and it will be time to break our programs into pieces.

Summer 2007CISC121 - Prof. McLeod37 Primitive Types Unfortunately not everything in Java is an Object. Primitive Types are used to declare variables that themselves will not be Objects either. This is done for convenience and more efficient use of memory. Primitive Type variables fall into the categories of integer types, real types, characters and booleans.

Summer 2007CISC121 - Prof. McLeod38 Integer Primitive Types byte, short, int, long For byte, from -128 to 127, inclusive (1 byte). For short, from to 32767, inclusive (2 bytes). For int, from to , inclusive (4 bytes). For long, from to , inclusive (8 bytes). A “byte” is 8 bits, where a “bit” is either 1 or 0.

Summer 2007CISC121 - Prof. McLeod39 Aside - Number Ranges Where do these min and max numbers come from? Memory limitations and the system used by Java (two’s complement) to store numbers determines the actual numbers. The Wrapper classes can be used to provide the values - for example: Integer.MAX_VALUE// returns the value More on these topics later!

Summer 2007CISC121 - Prof. McLeod40 Real Primitive Types Also called “Floating Point” Types: float, double For float, (4 bytes) roughly ±1.4 x to ±3.4 x to 7 significant digits. For double, (8 bytes) roughly ±4.9 x to ±1.7 x to 15 significant digits.

Summer 2007CISC121 - Prof. McLeod41 Character Primitive Type char from '\u0000' to '\uffff' inclusive, that is, from 0 to (base 10) or 0 to ffff (base 16, or “hexadecimal”). A variable of the “ char ” type represents a Unicode character. Can also be represented as ‘a’ or ‘8’, etc.

Summer 2007CISC121 - Prof. McLeod42 Boolean Primitive Type boolean is either true or false.

Summer 2007CISC121 - Prof. McLeod43 Primitive Types, Cont. Everything else in Java is an Object. The rest of the language consists of: –literal values –operators –keywords –“punctuation”

Summer 2007CISC121 - Prof. McLeod44 String Objects String ’s are not primitive data types, but are Objects. A String is declared in the same way as a primitive type using the keyword: String.

Summer 2007CISC121 - Prof. McLeod45 Variable Declaration Java is a “declarative” language. In other words, variables must be declared before they can be used. To declare a variable, use the Java “keyword” appropriate for the type of variable you are declaring followed by a variable name you have created, followed by a semicolon. Examples: int aNum; char aLetter; double totalVolume; String userPrompt;

Summer 2007CISC121 - Prof. McLeod46 Legal Variable Names Java names may contain any number of letters, numbers and underscore (“_”) characters, but they must begin with a letter. Standard Java Naming Convention: –Names beginning with lowercase letters are variables or methods. –Names beginning with uppercase letters are class names. –Successive words within a name are capitalized (“camel case”). –Names in all capital letters are constants. (We’ll get to “constants” shortly).

Summer 2007CISC121 - Prof. McLeod47 Literal Values Integers, for example: If you write these kinds of numbers into your program, Java will assume them to be of type “ int ”, and store them accordingly. If you want them to be of type “ long ”, then you must append a “ L ” to the number: 43L L L

Summer 2007CISC121 - Prof. McLeod48 Literal Values - Cont. Real or “Floating Point” numbers, for example: E E45 These literals will be assumed to be of the “ double ” type. If you want them to be stored as “ float ” types, append an “ F ”: 3.456F5.678E-10F-321.0F

Summer 2007CISC121 - Prof. McLeod49 Literal Values - Cont. char literals: ‘A’‘5’‘\u0032’ boolean literals: truefalse String literals: “Hello there!”“456.7”“West of North”

Summer 2007CISC121 - Prof. McLeod50 Variable Declaration - Cont. int and double variables initially are given a value of zero unless they are initialized to a value. Java may prevent you from using variables that are not initialized. So, it is sometimes good practice to initialize your variables before use, for example: int numDaysInYear = 365; double avgNumDaysInYear = ; String greetingLine = “Hello there!”; long counter = 0;

Summer 2007CISC121 - Prof. McLeod51 Variable Declaration - Cont. All these statements could be carried out in two lines, for example: int numDaysInWeek = 7; Is the same as: int numDaysInWeek; numDaysInWeek = 7;

Summer 2007CISC121 - Prof. McLeod52 Constants The Java keyword, “final” can be used to make sure a variable value is no longer “variable”. It becomes a constant, because Java will not allow your program to change its value once it has been declared: final int NUM_DAYS_IN_YEAR = 365; final double MM_PER_INCH = 25.4;

Summer 2007CISC121 - Prof. McLeod53 Type Casting When a value of one type is stored into a variable of another type. Casting in one direction is automatic, you do not have to deliberately or “explicitly” cast: A value to the left can be assigned to a variable to the right without explicit casting: byte > short > int > long > float > double

Summer 2007CISC121 - Prof. McLeod54 Type Casting - Cont. For example in the statement: double myVar = 3; the number 3 is automatically cast to a double (3.0) before it is stored in the variable “ myVar ”. However, if you tried the following: int anotherVar = ; the compiler would protest loudly because a double cannot be stored in an int variable without loss of precision. Wrong direction!

Summer 2007CISC121 - Prof. McLeod55 Type Casting - Cont. If you really want to cast in the other direction, then you must make an explicit cast. For example: int anotherVar = (int) ; is legal. The “ (int) ” part of the statement casts the double to an int. The variable anotherVar would hold the value 345 Note how numbers are truncated, not rounded when casting!

Summer 2007CISC121 - Prof. McLeod56 Arithmetic Operators The standard binary arithmetic operators in Java are: –Addition ( + ) –Subtraction ( - ) –Multiplication ( * ) –Division ( / ) –Modulus or Remainder ( % ) (ie. 12 % 5 yields 2 ) All of these operations apply to all numeric primitive data types. All require values on both sides of the operator (why they are called “binary operators”).

Summer 2007CISC121 - Prof. McLeod57 Integer Arithmetic Arithmetic operations between integers produce integer results by truncating the answer — fractional parts are discarded Examples: 3 / 4 stores as 0 4 / 4 stores as 1 5 / 4 stores as 1 Integer arithmetic is unsuitable for calculations involving real-world continuous quantities

Summer 2007CISC121 - Prof. McLeod58 Real or Floating Point Arithmetic Floating-point arithmetic is used with float and double values. It produces the expected results: 4.0 / 3.0 = However, these numbers have range and precision limits: TypeRangePrecision float ± decimal digits double ± decimal digits

Summer 2007CISC121 - Prof. McLeod59 Mixed Type Arithmetic Expressions Suppose you have a “mixed type” expression involving an arithmetic operator. To evaluate the expression, Java will cast one side to match the other. For example if one side is an int and the other side is a double, the int will be automatically cast to a double before the operation takes place. For example: 9 / 2 stores as 4 9 / 2.0 stores as * 12 stores as * 12 stores as 48.0

Summer 2007CISC121 - Prof. McLeod60 Strings and the “ + ” Operator Not only can “ + ” operate on numeric values, but it can also handle String ’s on either or both sides. If one side is not a String, it will be changed to one, and then it will be concatenated to the String on the other side: 4 + “you” stores as “4you” “apples” + “oranges” stores as “applesoranges99” “little piggies” stores as “10little piggies” Expressions are evaluated from left to right, unless precedence rules apply.

Summer 2007CISC121 - Prof. McLeod61 Unary Arithmetic Operators Unary operators include “ + ” and “ - ”, where “ -aNum ” negates the value produced by aNum, for example. They also include the increment ( ++ ) and decrement ( -- ) operators which increase or decrease an integer value by 1. Preincrement and predecrement operators appear before a variable. They increment or decrement the value of the variable before it is used in the expression. Example: int i = 4, j = 2, k; k = ++i - j; // i = 5, j = 2, k = 3

Summer 2007CISC121 - Prof. McLeod62 Unary Arithmetic Operators - Cont. Postincrement and postdecrement operators appear after a variable. They increment or decrement the value of the variable after it is used in the expression. Example: int i = 4, j = 2, k; k = i++ - j; // i = 5, j = 2, k = 2 Keep expressions involving increment and decrement operators simple!

Summer 2007CISC121 - Prof. McLeod63 Assignment Operators = set equal to *= multiply and set equal to /= divide and set equal to -= subtract and set equal to += add and set equal to

Summer 2007CISC121 - Prof. McLeod64 Assignment Operators - Cont. An assignment statement in Java has the form variableName = expression; The expression is evaluated, and the result of the expression is stored in the specified variable. Assignment statements and arithmetic operations can be combined in a single symbol. For example, variableName += expression; is equivalent to variableName = variableName + expression;

Summer 2007CISC121 - Prof. McLeod65 Logical Binary Operators Return either true or false. == equals to != not equals to > greater than < less than >= greater than or equal to <= less than or equal to &, && logical “And” |, || logical “Or”

Summer 2007CISC121 - Prof. McLeod66 Aside – “ | ” or “ || ”? What’s the difference? A single “ | ” or “ & ” always evaluates both sides of the expression, whether it is necessary or not. “ && ” stops if the left side is false, “ || ” stops if the left side is true. When would this make a difference? For example: int x = 0, y = 4; boolean test = x != 0 & y / x > 1; –Gives an error, using “ && ” would not. Why?

Summer 2007CISC121 - Prof. McLeod67 Logical Operators - Cont. The one “unary” logical operator is “ ! ”. Called the “Not” operator. It reverses the logical value of a boolean. For example: !(5 > 3) evaluates to false

Summer 2007CISC121 - Prof. McLeod68 Logical Operators - Cont. “Truth” tables for the “And” and “Or” operators: && testa testbtruefalse true false || testa testbtruefalse true falsetruefalse

Summer 2007CISC121 - Prof. McLeod69 Precedence Rules Operator precedence rules determine which operations take place in what order: –Unary operations including casting, are done first. –Then *, /, % –Then +, - –Then, = –Then ==, != –Then &, &&, |, || –Then =, *=, +=, -=, /= Use “( )” to control order of operations, as the expression inside “( )” will be evaluated before stuff outside of “( )”.

Summer 2007CISC121 - Prof. McLeod70 Expressions Expressions are combinations of variables, literal values, and operators. For example: int aNum = * 7;// aNum is 25 int aNum = (4 + 3) * 7;// aNum is 49 (4 > 7) || (10 > -1)// yields true (5.5 >= 5) && (4 != 1.0)// yields true double circ = 3.14 * 2 * r; …