COMP 14 Introduction to Programming

1
COMP 14Introduction to Programming

• Basic Elements of Java, Part 1
• Jason Jerald
• Monday June 26, 2006

2
Announcements

• Pledge
• If you have not handed in your pledge please do
  so ASAP
• New office hours
• Tues/Thurs 200-300
• Mon/Wed/Friday 1130-1230
• By appointment
• Assignment 1
• Some of you have not handed in yet
• This time I will only deduct 10 per day
• Assignment 2?
• Questions?

3
Review Exercise

• Execution of c2ab in a computer
• Take the value of a
• Multiply it by 2
• Take the value of b
• Add b to the previous result
• Put final result into c

4
Reading Check-Up

• The ________ rules of a language determine which
  instructions are valid.
• True or False? Hello! is an example of a legal
  Java identifier. _______
• If an operator has an integer and a
  floating-point operand, the result of the
  operation is a ___________ number.
• The expression (int) (9.2) evaluates to ___.

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Lecture Objectives

• Overview of Java
• Discover what a compiler is and what it does
• Examine how a Java program is processed
• Examine a Java program
• Java Syntax and Semantics
• Become familiar with the basic components of a
  Java program, including methods, special symbols,
  and identifiers.
• Explore primitive data types.
• Discover how to use arithmetic operators.
• Examine how a program evaluates arithmetic
  expressions.
• Explore how mixed expressions are evaluated.
• Learn about type casting.
• Introduction to the String class

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Programming Languages

• Programming language
• a set of rules, symbols, and special words
• Yesterday we talked about
• machine language
• assembly language
• High-level languages make programming easier
• Closer to spoken languages
• Examples
• Basic
• FORTRAN
• COBOL
• C/C
• Java

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Java and Machine Language

• To run a Java program
• Java instructions need to be translated into an
  intermediate language called bytecode.
• The bytecode is interpreted into a particular
  machine language.

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Compiler

• Compiler
• A program that translates a program written in a
  high-level language into the equivalent machine
  language.
• In the case of Java, this machine language is the
  bytecode.
• Java Virtual Machine (JVM)
• A hypothetical computer developed to make Java
  programs machine independent.

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Processing a Java Program

• Program
• written in Java using the Editor and compiled to
  Bytecode using the Compiler.
• Loader
• transfers the compiled code (bytecode) into main
  memory and loads the necessary Libraries.
• Interpreter
• reads and translates each bytecode instruction
  into machine language and then executes it.

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A Java Program

• 1 public class DebuggerExample
• 2
• 3 public static void main(String args)
• 4
• 5 int sumOfTwoAndThree, sumOfSevenAndEight
• 6
• 7 System.out.println("A simple Java
  program.")
• 8
• 9 sumOfTwoAndThree 23
• 10 System.out.println("The sum of 2 and 3
  " sumOfTwoAndThree)
• 11
• 12 sumOfSevenAndEight 7 8
• 13 System.out.println("7 8 "
  sumOfSevenAndEight)
• 14
• 15
• Sample Run
• My first Java program.
• The sum of 2 and 3 5

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Debugger / Breakpoints

• Demo

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Programming Languages

• Programming languages have rules of grammar just
  as English does
• syntax rules - which statements are legal and
  which are not
• semantic rules - determine the meaning of the
  instructions
• token - smallest individual unit of a program
• special symbols
• word symbols
• identifiers

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The Java Programming Language

• Java program A collection of classes
• There is a main method in every Java application
  program
• Token The smallest individual unit of a program

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Basic Java Syntax and Semantics

• Java Basics
• Tokens
• special symbols
• word symbols
• Identifiers
• data types
• boolean
• integer
• float-point
• Arithmetic operators and expressions
• , -, , /,

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Special Symbols
- / . ? , lt ! gt
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Word Symbolsaka reserved words, or keywords

• int
• float
• double
• char

• void
• public
• static
• throws
• return

• reserved words are always all lowercase
• each word symbol is considered to be a single
  symbol
• cannot be used for anything other than their
  intended
• purpose in a program
• shown in blue typewriter font in textbook
• full table in Appendix A

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Identifiers

• Names of things (variables, constants, methods)
  in your programs
• Can be composed of any combination of letters,
  digits, underscore (_), and dollar sign ()
• Cannot begin with a digit
• May be any length
• Java is case-sensitive
• Total, total, and TOTAL are different identifiers

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Illegal Identifiers
19
Questions

• Classify the following as legal or illegal
  identifiers
• My First Program ____
• my1stProgram ____
• 1stProgram ____
• money ____
• an_identifier ____
• Jane'sProgram ____

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Primitive Data TypesWhats A Data Type?

• A set of values and the operations that can be
  performed on those values
• Primitive data are fundamental values such as
  numbers and characters
• Operations are performed on primitive types using
  built-in operators

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Primitive Data Types

• 8 primitive data types in Java
• 4 represent integers
• byte, short, int, long
• 2 represent floating point numbers
• float, double
• 1 represents characters
• char
• 1 represents boolean values
• boolean

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Primitive Data TypesBooleans

• Only two valid values
• true or false
• uses 1 bit for storage
• Represent any situation that has 2 states
• on - off
• true - false
• true and false are reserved words

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Primitive Data TypesNumeric Types

• The difference between the various numeric
  primitive types is their size, and therefore the
  values they can store

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Integers

• Examples -6728, -67, 0, 78, 36782
• Positive integers do not require a '' sign in
  front of them (but they can)
• No commas are used in an integer
• commas in Java are used to separate items in a
  list

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Primitive Data TypesCharacters

• A char stores a single character from the Unicode
  character set
• an ordered list of characters, and each character
  corresponds to a unique number
• uses 16 bits per character, allowing for 65,536
  unique characters
• Character literals are delimited by single
  quotes
• 'a' 'X' '7' ' ' '' ',' '\n'

newline character (we'll discuss later)
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Floating-Point Data Types

• Two types of floating-point data types
• float
• double
• A double is more precise than a float but
• A double takes up more space
• A double calculation takes longer to computer

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Break

• Do something here to keep people from falling
  asleep

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Arithmetic Expressions

• Expression - a combination of one or more
  operands and their operators
• Arithmetic expressions compute numeric results
  and make use of the arithmetic operators
• If either or both operands associated with an
  arithmetic operator are floating point, the
  result is a floating point

Addition Subtraction - Multiplication Div
ision / Modulus (Remainder)
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Division and Remainder

• If both operands to the division operator (/) are
  integers, the result is an integer (the
  fractional part is discarded)
• The modulus, or remainder, operator () returns
  the remainder after dividing the second operand
  into the first (only works with integer types)

0
8 / 12 equals?
14 / 3 equals?
4
8
8 12 equals?
14 3 equals?
2
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Unary vs. Binary Operators

• Unary operators
• has only one operand
• example - (negative, not subtraction)
• -5
• Binary operators
• has two operands
• example - (subtraction)
• 5 - 3

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Operator Precedence

• Order in in which operators are evaluated
• multiplication, division, and remainder
• addition, subtraction
• arithmetic operators with the same precedence are
  evaluated from left to right
• Parentheses can be used to force the evaluation
  order (just like in math)

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Operator Precedence

• What is the order of evaluation in the following
  expressions?

a b c d e
a b c - d / e
1
4
3
2
3
2
4
1
a / (b c) - d e
2
3
4
1
a / (b (c (d - e)))
4
1
2
3
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Integral Expressions

• All operands are integers
• Result is an integer
• Examples
• 2 3 5
• 3 x y / 7
• x 2 (y z) 18

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Floating-point Expressions

• All operands are floating-point numbers
• Result is a floating-point
• Examples
• 12.8 17.5 34.50
• x 10.5 y - 16.2
• 7.0 / 3.5

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Mixed Expressions

• Integer operands yield an integer result
• Floating-point operands yield a floating-point
  result
• If both types of operands are present, the result
  is a floating-point number
• implicit type coercion
• Precedence rules are followed
• Examples
• 2 3.5 ________
• 6 / 4 3.9 ________________

2.0 3.5
1 3.9 1.0 3.9
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Type Conversion (Casting)

• Used to avoid implicit type coercion
• Syntax
• (dataTypeName) expression
• Expression evaluated first, then type converted
  to dataTypeName
• Examples
• (int) (7.9) (int)(6.7) 13
• (int) (7.9 6.7) 14

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QuestionsEvaluate These Expressions
9 6 3

• (5 4) 6
• (5 6) 3.5
• (double) (13) / 2
• (double) (13 / 2)

11 3.5 not possible
13.0 / 2 6.5
(double) (6) 6.0
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The class String

• The class String is used to manipulate strings
• String
• sequence of zero or more characters
• enclosed in double quotation marks
• null or empty strings have no characters
• numeric strings consist of integers or decimal
  numbers
• length is the number of characters in a string
• Examples
• "Hello World"
• "1234"
• "45.67"
• ""

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Strings

• Every character has a position in the string
  (starting with 0)
• "Hello World"
• The length of the string is the number of
  characters in it
• what's the length of "Hello World"?

0123456789...
11 (count the space)
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Parsing Numeric Strings

• In Java, input from the user often comes in the
  form of a string
• we need to know how to get the number values out
  of the string
• Numeric String
• a string with only integers or decimal numbers
• "6723", "-823", "345.76"

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Parsing Numeric Strings

• String to int
• Integer.parseInt(strExpression)
• Integer.parseInt("6723") 6723
• String to float
• Float.parseFloat(strExpression)
• Float.parseFloat("345.76") 345.76
• String to double
• Double.parseDouble(strExpression)
• Double.parseDouble("1234.56") 1234.56

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Summary

• Identifiers
• can be composed of any combination of letters,
  digits, underscore (_), and dollar sign ()
• cannot begin with a digit
• Java is case-sensitive
• Data Types
• main integer type int
• main floating-point type double
• others char, boolean

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Summary

• Arithmetic Operators
• If one of the operands is floating-point, the
  result is a floating-point
• Can only use with two integer operands
• Casting
• (int) (54.9) - truncates the floating-point
  number
• (double) (23) - adds a .0 to the integer

addition subtraction - multiplication div
ision / remainder (mod)
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To do

• Homework 2 due Wednesday night
• Finish reading ch. 2 (pp. 64-99)
• Quiz tomorrow
• Covering chapters 1 and 2
• Write in your own words an overview (1/2 page)
  of chapter 2
• Write a simple algorithm
• Basic Java syntax
• Other basic questions
• Questions?