MSI 692: Special Topics in Information Technology

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• MSI 692 Special Topics in Information Technology
• Sanjay Goel
• University at Albany, SUNY
• Fall 2004

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Outline for the ClassPart 1

• Introduction
• What is Java?
• How is Java different from other languages?
• Tools for Programming in Java
• Java Language Lexical elements
• Keywords
• Identifiers
• Literals
• Operators
• Punctuation

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Outline for the ClassPart 2

• Data Types
• Variables and initializations
• Methods
• Numbers
• Types
• Ranges
• Expressions
• Conversions
• Operators
• Assignment and Increment
• Precedence and Associativity

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Programming
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ProgrammingWhy do we need to write programs?

• Humans talk in a different language than
  computers do and we need to translate human talk
  into computer talk or instructions.
• You write the program in a language you are
  comfortable with
• The compiler takes your program and smooshes it,
  digests it, and creates a stream of zeros and
  ones for the computer to understand.
• Normally, different computers have different
  languages that they understand similar to the
  various human languages (i.e. French, English,
  Sanskrit German)
• Thus, we have different compilers for different
  computers.

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ProgrammingWhat are the advantages of Java?

• Eliminates pitfalls of C/C by eliminating
  pointer arithmetic and explicit memory
  management.
• Is object-oriented which helps enforce better
  programming techniques and to better visualize
  the code
• Interpreted environment which improves speed of
  development
• Reduces compile-link-load cycle
• Is portable across multiple platforms
• Runs more than one parallel activity via threads
• Enables security by checking code modules that
  are loaded

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ProgrammingHow is Java different from other
languages?

• Uses a Java Virtual Machine (JVM)
• JVM is a byte-code interpreter unique for
  different hardware
• Takes burden of compling on multiple hardware
  away from user
• C/C Source ? Compiler ? Machine Code
• Java Source ? Java Compiler ? Byte Code ? Java
  Virtual Machine ? Machine Code
• Garbage Collection
• No memory management
• Code Security

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ProgrammingWhat are the advantages?

• Expands your programming horizons across the
  enterprise
• You are able to write programs which span across
  the internet
• You can have a database sitting in one location
  on a compute server in another location and a web
  server in a third place which will communicate
• Java makes it easier to program across the
  network
• You can develop user interfaces
• All these facilities are available as extensions
  of the basic core Java language.
• We are going to focus on the core language in
  this class

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ProgrammingIDE Options

• Requirements for Development of Programs
• Editor (Emacs/Wordpad)
• Compiler (Java SDK for Windows)
• Execution Environment (Unix Shell/DOS Prompt)
• Several Different Development Environments exist
• BlueJ
• JBuilder
• Forte from Java
• JDeveloper from Oracle
• Java Visual Café
• If any one wants to install java on their
  personal computers a link to the instructions is
  located on the syllabus.
• Please interact with Tony Manes or D.J. Anderson
  with questions about this installation.
• Come to me if they are unavailable or unable to
  help.

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Language Constructs
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Language ConstructsIntroduction

• Like any language a programming language has some
  symbols and some rules to combine these symbols
  to make sense.
• A compiler breaks individual characters the
  program into tokens. These tokens are then
  interpreted with respect to the context they
  exist in and processed.
• Most of the previous languages were based on the
  127 ASCII characters
• Adequate representation to the English language
  keyboard.
• Java is based on Unicode that has 64000
  characters
• Allows representation of multiple languages other
  than English for programming.

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Language Constructs Types of Tokens

• There are five types of tokens which are
  processed
• Keywords
• Identifiers
• Literals
• Operators
• Punctuation
• There are two types of tokens that are not
  processed
• White Space
• Comments

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Language ConstructsWhite Space

• Uses
• Used to separate tokens in program that are not
  separated by separators
• Make the program more readable
•  There are three types of white spaces
• space (when you hit the space bar)
• tab (when you hit the tab key)
• newline (when you hit the newline key)

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Language Constructs Comments

• Comments are used for documenting the code.
• There are 3 types of comments
• Single line comments
• // This is a single line comment
• Multi-line comment
• /
• This is a multi-line comment
• So write multiple lines here or only one if you
  choose to
• /
• javadoc comments
• / This is a javadoc comment to generate
  documentation at the end
• of the code
• _at_author Sanjay Goel
• _at_deprecated
• /

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KeywordsReserved words with special meaning

• These are reserved words in the language and have
  a special meaning to them.
• There are 47 key words in Java language.
• The keyword is separated from other keywords or
  identifiers by white space, comment or
  punctuation.
• const and goto have no meaning in java but had
  meaning in C C.
• They have been included to facilitate error
  reporting when users use these words in java
• null, true and false are not keywords but are
  literals.

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KeywordsKeywords in Java

• The keywords in the Java language are as follows
• abstract double int strictfp
• boolean else interface super
• break extends long switch
• byte final native synchronized
• case finally new this
• catch float package throw
• char for private throws
• class goto protected transient
• const if public try
• continue implements return void
• default import short volatile
• do instanceof static while  

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IdentifiersNaming the Java elements

• These are the names that used to specify elements
  of the Java program, such as class variable or
  method i.e.
• These are the names that you assign to different
  constructs of the program.
• An identifier is any sequence of Java letters and
  digits.
• The first of that must be a Java letter.
• A key word can not be an identifier and the
  literals null, true and false can not be
  identifiers.
• Java letters include the upper and lower case
  letters of the English alphabet
• i.e. a-z, A-Z, , and underscore "_"
• Java digits are 0-9

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LiteralsValue representations for primitive
numeric types

• Java has built in types for numbers, characters
  and Booleans.
• It also has a built in class for String.
• Literals are the value representations for the
  primitive numeric types, the Boolean and
  character as well as the standard class type of
  String.
• String "Carrot
• String "Emily
• char 'a
• char 'b
• Boolean true
• Boolean false
• double 3.21
• int 12
• int 234234

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Operators Mathematical

• Operators
• /, , , -,
• Precedence
• Hierarchy that determines the order in which
  operators are evaluated
• Associativity
• Order in which operators of equal precedence are
  evaluated (Left to Right or Right to Left)
• BODMAS
• Binary operation of Division, Multiplication,
  Addition, Subtraction

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Operators Relational

• They determine the relationship between two
  operands (values).
• They are used in a condition expression in order
  to test whether a particular kind of relationship
  exists between two operands.
• All relational operators return a Boolean Value,
  which evaluates if the relationship between the
  operands is true or false.
• Java utilizes a conditional expression, which
  uses one or more relational operators to discover
  if the statement is true or false.

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Operators Relational

• Relational Operators
• Equal to
• Not equal to !
• Greater than gt
• Less than lt
• Greater than or equal to gt
• Less than or equal to lt
• Example The if..else statement. If the
  expression is true, execute the if statement, and
  if it is false, execute the else statement.
• b lt a
• If b is less than or equal to a, then the
  expression is true, and the if statement is
  executed. If b is greater than a, then the
  expression is false, and the else statement is
  executed.

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Operators Logical

• In order for Java to assess two relational
  expressions, they must be linked together using a
  logical operator.
• Logical Operators
• And
• OR ll
• And
• OR l
• Ternary if-then-else ?
• The AND Logical Operator ()- For the statement
  to be true, both relational expressions have to
  be true. If one or both of the expressions is
  false, then the AND logical operator returns a
  Boolean false.

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Operators Logical

• The OR Logical Operator (ll)- For the statement
  to be true, only one of the relational
  expressions has to be true. If both of the
  expressions are false, then the OR logical
  operator returns a Boolean false.
• The Single AND and OR Logical Operators (,l)-
  When using the and ll Operators, only the
  first expressions are evaluated. If the first
  expression is false in the Operator, then the
  second does not need to be evaluated. If the
  first expression is true in the ll Operator, then
  the second does not need to be evaluated.
  However, when using the single AND and OR
  Operators, both expressions need to be evaluated
  regardless of if they return a Boolean true or
  false.
• The Ternary Operator (?)- Uses a relational
  expression and two values. If the relational
  expression is true, the ternary operator uses the
  first value. If it is false, it uses the second
  value.

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Operators Bitwise

• Bitwise Operators help the programmer change the
  value of a bit (binary digit) from zero to one,
  or one to zero.
• Bitwise AND Operator ()- It compares two bits.
  If both of the bits are 1s, then the AND
  operator returns a 1. If only one bit is 1 or
  both are 0, then it returns a 0.
• Example 00001111
• 00001010
• 00001010
• Bitwise Inclusive OR Operator (l)- If one or both
  bits are a binary 1, then a binary 1 is returned.
  If both bits are a binary 0, then a binary 0 is
  returned.
• Example 00001111
• l 00001010
• 00001111

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Operators Bitwise

• Bitwise Exclusive OR Operator ()- If one bit is
  a binary 1, then a binary 1 is returned. If both
  bits are a binary 1, then a binary 0 is returned.
  If both bits are a binary 0, then a binary 0 is
  returned.
• Example- 00001111
• 00001010
• 00000101
• Bitwise Left Shift Operator (ltlt)- This operator
  moves bits one position to the left. Then
  leftmost bit then drops, and the rightmost bit is
  replaced with a 0.
• Example- 00001111 ? 00011110

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Operators Bitwise

• Bitwise Signed Right Shift Operator (gtgt)- This
  operator moves bits one position to the right.
  The empty position on the left is filled with a
  value that represents the same sign as the
  rightmost bit that was shifted. (positive bit
  0, negative bit 1)
• Example- 10001111 ? 10000111
• Bitwise Unsigned Right Shift Operator (gtgtgt)- This
  operator moves bits one position to the right.
  The empty position on the left is always filled
  with a binary 0 (the sign of the bit is not
  significant).
• Bitwise Complement Operator ()- This operator
  reverses the values of the bits. Binary 1s
  become Binary 0s, and vice versa.
• Example- 00001111 ? 11110000
• Twos Complement- This term refers to reversing
  all of the bits, and then adding 1 to the result.

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PunctuationSeparators

• These are the separators used in expressions i.e.
  
• ""
• ","
• "

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Data Types and Variable Declarations
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Data Types and Variable DeclarationsIntroduction

• Data type determines how data is represented in
  computer memory. Each variable has to have a
  defined type
• There are 8 primitive types.
• Numeric - byte, short, int, long, float, double
• Character char
• Logic - boolean (can have value of true or false)
• In addition there are built in classes like
  Button, Frame, Point, String.
• There are more than a few thousand classes and
  new classes are added continuously.
• There is a SUN community process that determines
  what new classes to add.
• The data values of classes are called objects.

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Data Types and Variable DeclarationsVariables

• These are identifiers that are used to refer to
  values stored in the computers memory.
• e.g. int i
• int j, k
• Variables can be initialized also
• e.g. int j 10
• boolean flag true, iflag false
• String sentence "Who am I"

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Number Types
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Number TypesTypes of Numbers

• Two types
• Integer representations
• Floating point representations
• A binary digit (bit) is the smallest unit of
  information that can be stored on the computer
  and can have a binary value i.e. 0 or 1.
• A combinations of bits is used to represent
  larger range of values.
• For integers bits are interpreted with the binary
  number system.
• Integers can be represented as a combination of
  binary digits or bits.
• Different precisions are used to store different
  numbers
• Negative numbers use twos complement
  representation
• Allows use of binary arithmetic operations on
  signed integers
• Positive 2's complement numbers are represented
  as simple binary.
• Negative 2's complement numbers are represented
  as the binary number that when added to a
  positive number of the same magnitude equals zero.

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Number TypesNegative Numbers and Floating Point
Types

• Integral Types

byte 8 -128 to 127
short 16 -32768 to 32767
char 16 0 to 65536
int 32 -2147483648 to 2147483647
long 64 -9223372036854775808 to 9223372036854775807

• Floating point types

Float 32 Precision 7 digits
Double 64 Precision 15 digits
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Number TypesArithmetic Expressions

• There are 5 basic arithmetic operators
• Addition
• Subtraction
• Multiplication
• Division
• Modulus

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Number TypesConversion

• Any primitive numeric types can be used with
  these arithmetic operators.
• If the operators are of different types the types
  are converted so that they are of the same type.
• This conversion scheme is called the binary
  numeric promotion.
• if either operand is double the other operand is
  converted to double
• else if either operand is float other operand is
  converted to float
• else if either operand is long other operand is
  converted to long
• else both operands are converted to int.

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Number TypesExplicit Type Conversions

• There are two type of conversions
• Widening primitive conversions
• These go from a lower resolution to a higher
  resolution type and thus there is no loss of
  information.
• These conversions are sometimes done via binary
  numeric promotion
• Example
• int x 1, y 2
• float z x y

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Number TypesExplicit Type Conversions contd

• Narrowing primitive conversions
• These go from a higher resolution type to a lower
  resolution type and can lead to loss of
  resolution.
• An explicit conversion is required via a cast
  operator to achieve this.
• This is dangerous and should be done carefully
• int i 127, j 128
• byte iAsByte (byte)i
• byte jAsByte (byte)j
• System.out.println(i)
• System.out.println(j)
• output
• 127
• -128
• Since the max positive number is 127 the number
  representation gets screwed up in memory.)

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Number TypesOperators

• Assignment operator "
• assigns the rhs to the lhs
• i.e. i 10
• - gtgt ltlt ! 
• Increment and decrement operators
• i --i i i--

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Number TypesAssociativity and precedence

• Precedence - hierarchy of evaluation
• Associativity - If level is the same what is the
  order of evaluation
• You can make the expression more explicit by
  using parentheses.
• e.g. a b c vs. (a b) c

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Building a Program
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Building a ProgramSample Program

• Let us examine a simple program
• Prior to dissecting this let us look at the
  various structures in the program.
• Just like in writing a book you construct the
  basic characters into words, words into
  statements, statements into paragraph and
  paragraphs into chapters and chapters into books.
  
• Similarly we can arrange the program constructs
  into a hierarchy.

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Building a ProgramMethods

• Methods are group of instructions with a name.
• You can write very simple programs in a single
  monolithic block but programs can get large and
  as large as a few million lines.
• You need to separate pieces out for ease of
  development and maintenance.
• The way to separate them is writing methods which
  are a group of instructions with a name and
  signature.
• Depending on the size of the program there can be
  many methods.
• Some methods are already defined in the language.
• main method
• The main method is a special method. The program
  starts execution from the main method.
• public static void main(String args)

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Building a ProgramWriting to console

• System.out.print(ln)
• System.out.print("I want to test without
  carriage return")
• System.out.println("I want to test with carriage
  return")

• Hello World program
• / Hello world program for class lecture
• _at_author Sanjay Goel
• _at_created August 26, 2001
• /
• import java.io.
•  
• public class HelloWorld
• public static void main(int args)
• String string1 "Hello "
• String string2 "World"
• System.out.println(string1 string2)

/ Program to sum two numbers
_at_author Sanjay Goel _at_created August 26,
2001 / import java.io.   public class
Sum int a 10 int b 30   int sum
a b   System.out.println("a " a " b
" b " Sum " sum)
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Review
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RecapKeywords and Identifiers

• Keywords
• Reserved words which have special purpose and
  cant be used for any thing else
• 47 in total new words may be added as language
  expands
• Identifiers
• Also called variables are names of the data
  elements which you have stored in memory
• Formed by sequence of Java letters and digits
• All keywords and three literals (true, false,
  null) can not be used as identifiers
• Note Java letters are A-Z, a-z, underscore
• Java numbers 0-9

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RecapLiterals

• Literals
• These are the values you assign to the variables
• The variables have to be of specific types
• Types of Literals
• Numeric
• Whole Numbers integer type numerics
• Fractional Numbers floating point type numerics
  
• Char
• single character, digit, symbol
• Boolean logic
• Strings
• Text

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RecapNumeric Types

• The numeric types are
• Byte 8 bits
• Short 16 bits
• Int 32 bits
• Char 32 bits
• Long 64 bits
• Float 32 bit
• Double 64 bits
• Why do we have so many different types?
• To economize on use of memory
• We use more memory for larger whole numbers or
  for fractional numbers with higher precision.
• The ranges were discussed in the previous class.

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RecapOperators, Punctuation, White Space
Comments

• Operators
• These are the symbols used for arithmetic
  operations on numbers
• Unary operators operate only on one number , --
• Binary operators operate on two numbers , -, /,
  
• Punctuation
• These are the elements that act as separators
• ,
• White Space
• Spaces, tabs, newline
• Comments
• Three types Single line, multiline, Javadoc
  comment

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RecapInitialization, Methods, and I/O

• Variable initialization
• Specify type, value, and name
• Terminated by a semicolon
• Methods
• User Defined
• System Defined
• Simple I/O
• System.out.println(This is a test)
• Console.in.readInt()

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RecapArithmetic Expressions and Conversion

• Arithmetic Expressions
• Syntax
• Mixed mode arithmetic
• Binary numeric promotion
• Type conversion
• Widening primitive conversions
• Goes from lower precision to higher precision
• Can be automatic or an explicit cast
• Narrowing primitive conversions
• Has to be explicit

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RecapArithmetic Operators, Associativity and
Precedence

• Arithmetic Operators
• Variable expression (a b c)
• Assignment (, , -, , /, )
• Increment and Decrement Operators (, -)
• Precedence
• order in which operators are evaluated
• Associativity
• Order in which operators of same precedence are
  evaluated (L-gtR, R-gtL)
• You can make the expression more explicit by
  using parentheses.