IFI7184.DT lesson1- Programming languages

IFI7184.DT – Lesson 1
Introduction and contextualization
@ slides adapted from Isaías da Rosa sources

Outline
Java programing language
Object-oriented concepts
Java IDEs
Eclipse working environment
Variables and Types
Strings
Variables and Assignment
Primitive Data Types
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Java programming language
• Dynamic Web applications
– Servlets, JSP
• Native applications
– Android and blackberry
• Java is not
– Javascript
– Native IOS
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Java is…
• A complied language
– Has restrictive rules but is not difficult
• Similar languages
– C, C + +, c#, Javascript, PHP
• Although…
– You need to understand
• Rules – basic programming vocabulary
• The principles of object-oriented language
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First steps on Java
• Basic Structure
– Object-oriented concepts
• Understand programming concepts like
– What is a statement
– What is a variable
– What is a function
– What is a condition
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Development Environments
• Applications that support Java development:
– Eclipse SE Development Kit (JDK)
• Runtime, compiler and other tools
– NetBeans
– BlueJ
• Though the details of these environments
differ,
– the basic compilation and execution process is
essentially the same
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Java Translation
• Java is an
– interpreted language
– Is portable
• The Java compiler translates into
– Java bytecode
• We will use a Java virtual machine
– Eclipse
7
Java source
code Java
bytecode
Java
compiler
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Basic Program Development
errors?
errors?
Edit and
save program
Compile program
Execute program and
evaluate results
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Runtime Architecture
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Operating System
Java Virtual Machine (JVM)
Core runtime and additional libraries
Compiled bytecode

Java Translation
Java source
code
Machine
code
Java
bytecode
Bytecode
interpreter
Bytecode
compiler
Java
compiler
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Outline
Java IDEs
Variables and Types
Strings
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• What is an Object?
– An object-oriented -> aims to -> model real-world
objects
• examples of real-world objects: dog, desk, computer,
bicycle
– Characteristics of real-world object
• have state and behaviour
– State = name, color, breed, hungry
– Behaviour = barking, fetching, wagging tail
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A bicycle modeled as a object
State
Variables (fields)
behaviours
functions (methods)
speed
Pedal cadence
gear
that allow to change the state
Function to change the gear (bicycle has 3 gears)
1. Reject values < 1
or > than 3
2. Verify what is the
current gear
3. Change the gear

What we know
• What are variables -> state
– state of an object in real-world
• What are functions (methods) -> behaviours
– Behaviour of that object in real world
• But…
– Take the bicycle example
• 1 model/brand can have similar types of bicycle
• How to represent in object-oriented terms?
– Using classes

What Is a Class?
• A Class represent 1 object (bicycle)
– or 1 or more objects (bicycles)
• Objects with similar characteristics of Object bicycle:
– Same model, same company, same set of blueprints, same
components
Instance
Of
class of objects known as bicycles
object

What Is a Inheritance?
• Represent 1 object (bicycle)
– Which shares
• general and specific characteristics
– Object bicycle:
• Shared characteristics
– class bicycles
• Specific characteristics
– superclass – MountainBike and TandemBike
– How do you represent as object term?
inherit
characteristics
class of objects known as bicycles
Superclass of objects known as specific characteristic

A class in java
• Java includes a library of classes
• Java program is made of an aggregation of
– 1 or + classes - package
– Most common used is
• Java.lang (Packages)
• Search on google for java 6 api docs
• We are going to use
– The System class -> belongs to Java.lang
– The out variable -> PrintStream class -> System class
– Print method - println

Outline
Java IDEs
Variables and Types
Strings
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Java Development kit
• Includes
– Compiler - command javac
– Runtime - java
– Package - jar
– Documentation builder - javadoc

Java Application
• Consists
– Of many classes (.java) – command line runtime
– The packager (jar) – aggregates the many
classes
– The javadoc – the documentation builder
– The command line compiler - javac

First step
• Set up the workspace
• Create 1 application
– Create a project
– SRC AND BIN folders
• Every Java App Is Build Inside A Class
• Create a new class
– System.out.println(“Hello World”)
– Compile or run java application

Eclipse IDE

public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello world" );
}
}
Java Program Structure
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Hello World!
Class declaration
File name: HelloWorld.java Java is Case sensitive Language
=
Main method
Executable code
Compile results
File sources
HelloWorld.class
HelloWorld.java
Bytecode file
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Java syntax
The method can
be called
anywhere
A method contains
1 program statements
public class MyProgram
{
}
// comments about the class
public static void main (String[] args)
{
}
// Main method declaration
method header
method body
Don’t have to
create a
instance of a
class
Do not return
anything from
the class
New public
class called
MyProgram
class
body

The println Method
• The println method prints a character
string
• The System.out object represents a
destination (the monitor screen) to which
we can send output
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System.out.println ("Whatever you are, be a good one.");
information provided
(arguments)
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Resulting files

Errors
• A program can have three types of errors
1) Compile-time errors
• The compiler will find syntax errors and other basic
problems
• If compile-time errors exist, an executable version of the
program is not created
2) Run-time errors
• A problem can occur during program execution, such as
– trying to divide by zero, which causes a program to terminate
abnormally
3) Logical errors
• A program may run, but produce incorrect results, perhaps
using an incorrect formula

Comments
• Comments should always be included
– To explain the purpose of the program; and
– Describe processing steps.
• They do not affect how a program works
• Java comments can take three forms:
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// this comment runs to the end of the line
/* this comment runs to the terminating
symbol, even across line breaks */
/** this is a javadoc comment */
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Java is Case sensitive
• Java is case sensitive:
– Total, total, and TOTAL are different
identifiers
• Rules on how to…
– use different case styles for different types of
identifiers
• Class names start with upper case – MyProgram
• Variables with lower case - value

Reserved words
• Identifiers with a predefined meaning in the
language
– println
• A reserved word cannot be used in any
other way

Reserved Words
• The Java reserved words:
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abstract
assert
boolean
break
byte
case
catch
char
class
const
continue
default
do
double
else
enum
extends
false
final
finally
float
for
goto
if
implements
import
instanceof
int
interface
long
native
new
null
package
private
protected
public
return
short
static
strictfp
super
switch
synchronized
this
throw
throws
transient
true
try
void
volatile
while
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EXERCISE 1

Quick Check
Which of the following are valid Java identifiers?
grade
quizGrade
NetworkConnection
frame2
3rdTestScore
MAXIMUM
MIN_CAPACITY
student#
Shelves1&2
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Quick Check
Which of the following are valid Java identifiers?
grade
quizGrade
NetworkConnection
frame2
3rdTestScore
MAXIMUM
MIN_CAPACITY
student#
Shelves1&2
Valid
Valid
Valid
Valid
Invalid – cannot begin with a digit
Valid
Valid
Invalid – cannot contain the '#' character
Invalid – cannot contain the '&' character
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Outline
Java IDEs
Variables and Types
Strings
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Character Strings
• A string literal is represented by putting
double quotes around the text
• Examples:
"This is a string literal."
"123 Main Street"
"X”
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EXERCISE 2

//********************************************************************
// Countdown.java Author: Lewis/Loftus
//
// Demonstrates the difference between print and println.
//********************************************************************
public class Countdown
{
//-----------------------------------------------------------------
// Prints two lines of output representing a rocket countdown.
//-----------------------------------------------------------------
{
System.out.print ("Three... ");
System.out.print ("Two... ");
System.out.print ("One... ");
System.out.print ("Zero... ");
System.out.println ("Liftoff!"); // appears on first output line
System.out.println ("Houston, we have a problem.");
}
}
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//********************************************************************
// Countdown.java Author: Lewis/Loftus
//
// Demonstrates the difference between print and println.
//********************************************************************
public class Countdown
{
//-----------------------------------------------------------------
// Prints two lines of output representing a rocket countdown.
//-----------------------------------------------------------------
{
System.out.print ("Three... ");
System.out.print ("Two... ");
System.out.print ("One... ");
System.out.print ("Zero... ");
System.out.println ("Liftoff!"); // appears on first output line
System.out.println ("Houston, we have a problem.");
}
}
Output
Three... Two... One... Zero... Liftoff!
Houston, we have a problem.
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String Concatenation
• The string concatenation operator (+) is
used to append one string to the end of
another
"Peanut butter " + "and jelly"
• It can also be used to append a number to
a string
• A string literal cannot be broken across
two lines in a program
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EXERCISE 3

//********************************************************************
// Facts.java Author: Lewis/Loftus
//
// Demonstrates the use of the string concatenation operator and the
// automatic conversion of an integer to a string.
//********************************************************************
public class Facts
{
//-----------------------------------------------------------------
// Prints various facts.
//-----------------------------------------------------------------
{
// Strings can be concatenated into one long string
System.out.println ("We present the following facts for your "
+ "extracurricular edification:");
System.out.println ();
// A string can contain numeric digits
System.out.println ("Letters in the Hawaiian alphabet: 12");
continue
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continue
// A numeric value can be concatenated to a string
System.out.println ("Dialing code for Antarctica: " + 672);
System.out.println ("Year in which Leonardo da Vinci invented "
+ "the parachute: " + 1515);
System.out.println ("Speed of ketchup: " + 40 + " km per year");
}
}
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continue
// A numeric value can be concatenated to a string
System.out.println ("Dialing code for Antarctica: " + 672);
System.out.println ("Year in which Leonardo da Vinci invented "
+ "the parachute: " + 1515);
System.out.println ("Speed of ketchup: " + 40 + " km per year");
}
}
Output
We present the following facts for your extracurricular edification:
Letters in the Hawaiian alphabet: 12
Dialing code for Antarctica: 672
Year in which Leonardo da Vinci invented the parachute: 1515
Speed of ketchup: 40 km per year
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String Concatenation
• The + operator is also used for arithmetic addition
– The function that it performs depends on the type of the
information on which it operates
• If both operands are strings, or if one is a string and one is a
number,
– it performs string concatenation
• If both operands are numeric, it adds them
• The + operator is evaluated left to right, but parentheses
can be used to force the order
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EXERCISE 4

//********************************************************************
// Addition.java Author: Lewis/Loftus
//
// Demonstrates the difference between the addition and string
// concatenation operators.
//********************************************************************
public class Addition
{
//-----------------------------------------------------------------
// Concatenates and adds two numbers and prints the results.
//-----------------------------------------------------------------
{
System.out.println ("24 and 45 concatenated: " + 24 + 45);
System.out.println ("24 and 45 added: " + (24 + 45));
}
}
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//********************************************************************
// Addition.java Author: Lewis/Loftus
//
// Demonstrates the difference between the addition and string
// concatenation operators.
//********************************************************************
public class Addition
{
//-----------------------------------------------------------------
// Concatenates and adds two numbers and prints the results.
//-----------------------------------------------------------------
{
System.out.println ("24 and 45 concatenated: " + 24 + 45);
System.out.println ("24 and 45 added: " + (24 + 45));
}
}
Output
24 and 45 concatenated: 2445
24 and 45 added: 69
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EXERCISE 5

Quick Check
• What output is produced by the following?
51
System.out.println ("X: " + 25);
System.out.println ("Y: " + (15 + 50));
System.out.println ("Z: " + 300 + 50);
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Quick Check
X: 25
Y: 65
Z: 30050
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System.out.println ("X: " + 25);
System.out.println ("Y: " + (15 + 50));
System.out.println ("Z: " + 300 + 50);
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EXERCISE 6

Quick Check
54
System.out.println ("I said "Hello" to you.");
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Quick Check
An escape sequence begins with a backslash
character ()
55
• The compiler becomes confuse
– would interpret the second quote as the end
of the string
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EXERCISE 7

Escape Sequences
• Some Java escape sequences:
57
Escape Sequence
b
t
n
r
"
'

Meaning
backspace
tab
newline
carriage return
double quote
single quote
backslash
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//********************************************************************
// Roses.java Author: Lewis/Loftus
//
// Demonstrates the use of escape sequences.
//********************************************************************
public class Roses
{
//-----------------------------------------------------------------
// Prints a poem (of sorts) on multiple lines.
//-----------------------------------------------------------------
{
System.out.println ("Roses are red,” + “Violets are blue," +
"Sugar is sweet,ntBut I have "commitment issues",nt" +
"So I'd rather just be friendsntAt this point in our " +
"relationship.");
}
}
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//********************************************************************
// Roses.java Author: Lewis/Loftus
//
// Demonstrates the use of escape sequences.
//********************************************************************
public class Roses
{
//-----------------------------------------------------------------
// Prints a poem (of sorts) on multiple lines.
//-----------------------------------------------------------------
{
System.out.println ("Roses are red,ntViolets are blue,n" +
"Sugar is sweet,ntBut I have "commitment issues",nt" +
"So I'd rather just be friendsntAt this point in our " +
"relationship.");
}
}
Output
Roses are red,
Violets are blue,
Sugar is sweet,
But I have "commitment issues",
So I'd rather just be friends
At this point in our relationship.
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EXERCISE 8

Quick Check
• Write a single println statement that
produces the following output:
61
"Thank you all for coming to my home
tonight," he said mysteriously.
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• Write a single println statement that
produces the following output:
Quick Check
"Thank you all for coming to my home
tonight," he said mysteriously.
System.out.println (""Thank you all for " +
"coming to my homentonight," he said " +
"mysteriously.");
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Outline
Java IDEs
Variables and Types
Strings
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EXERCISE 9

Variables
• A variable is a name for a
– location in memory that holds a value
• When you declare a variable (variable declaration)
– you need to specify
65
int total;
int count, temp, result;
Multiple variables can be created in one declaration
data type variable name
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Variable Initialization
• You can add a initial value to your variable
66
int sum = 0;
int base = 32, max = 149;
data type variable name variable value = 0
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EXERCISE 10

//********************************************************************
// PianoKeys.java Author: Lewis/Loftus
//
// Demonstrates the declaration, initialization, and use of an
// integer variable.
//********************************************************************
public class PianoKeys
{
//-----------------------------------------------------------------
// Prints the number of keys on a piano.
//-----------------------------------------------------------------
{
int keys = 88;
System.out.println ("A piano has " + keys + " keys.");
}
}
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//********************************************************************
// PianoKeys.java Author: Lewis/Loftus
//
// Demonstrates the declaration, initialization, and use of an
// integer variable.
//********************************************************************
public class PianoKeys
{
//-----------------------------------------------------------------
// Prints the number of keys on a piano.
//-----------------------------------------------------------------
{
int keys = 88;
System.out.println ("A piano has " + keys + " keys.");
}
}
Output
A piano has 88 keys.
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Assignment
• An assignment statement
– Changes the value of a variable
• What happens?
• The value that was in total is overwritten
• You need to assign a value to a variable = variable's declared type
• Int , byte, short, long, float, double, boolean, char
• See more about primitive Data types
70
total = 55;
Assignment operator
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EXERCISE 11

//********************************************************************
// Geometry.java Author: Lewis/Loftus
//
// Demonstrates the use of an assignment statement to change the
// value stored in a variable.
//********************************************************************
public class Geometry
{
//-----------------------------------------------------------------
// Prints the number of sides of several geometric shapes.
//-----------------------------------------------------------------
{
int sides = 7; // declaration with initialization
System.out.println ("A heptagon has " + sides + " sides.");
sides = 10; // assignment statement
System.out.println ("A decagon has " + sides + " sides.");
sides = 12;
System.out.println ("A dodecagon has " + sides + " sides.");
}
}
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//********************************************************************
// Geometry.java Author: Lewis/Loftus
//
// Demonstrates the use of an assignment statement to change the
// value stored in a variable.
//********************************************************************
public class Geometry
{
//-----------------------------------------------------------------
// Prints the number of sides of several geometric shapes.
//-----------------------------------------------------------------
{
int sides = 7; // declaration with initialization
System.out.println ("A heptagon has " + sides + " sides.");
sides = 10; // assignment statement
System.out.println ("A decagon has " + sides + " sides.");
sides = 12;
System.out.println ("A dodecagon has " + sides + " sides.");
}
}
Output
A heptagon has 7 sides.
A decagon has 10 sides.
a dodecagon has 12 sides.
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Constants
• A constant is an identifier
– that is similar to a variable except that it holds the
same value during its entire existence
• As the name implies, it is constant, not variable
• The compiler will issue an error if you try to
change the value of a constant
• In Java, we use the final modifier to declare a
constant
final int MIN_HEIGHT = 69;
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Constants
• Constants are useful for three important reasons
1) First, they give meaning to otherwise unclear literal
values
• Example: MIN_HEIGHT means more than the literal 69
2) Second, they facilitate program maintenance
• If a constant is used in multiple places, its value need only be
set in one place
3) Third, they formally establish that a value should not
change,
• Avoiding inadvertent errors by other programmers

Outline
Java IDEs
Variables and Types
Strings
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Primitive Data
• There are eight primitive data types in Java
• Four of them represent integers:
– byte, short, int, long
• Two of them represent floating point numbers:
– float, double
• One of them represents characters:
– char
• And one of them represents boolean values:
– boolean

Most common Types
• int
– integer (most common. no decimal)
• long
– holds a really big integer
• float
– accurate up to 7 decimal places
• double
– accurate up to 15 decimal places I do believe (at work and don't have a book)
• boolean
– false or true (also 1 = true, 0 = false)
• string
– anything from numbers to letters to whole sentences. It will take the input
literately.
• char
– character, such as f or 6 or

Numeric Primitive Data
• The difference between the numeric
primitive types is their size and the values
they can store:
Type
byte
short
int
long
float
double
Storage
8 bits
16 bits
32 bits
64 bits
32 bits
64 bits
Min Value
-128
-32,768
-2,147,483,648
< -9 x 1018
- 3.4 x 1038 3.4 x 1038
- 1.7 x 10308 1.7 x 10308
Max Value
127
32,767
2,147,483,647
> 9 x 1018

Characters
• A char variable stores a single character
• Character literals are delimited by single quotes:
'a' 'X' '7' '$' ',' 'n'
• Example declarations:
char topGrade = 'A';
char terminator = ';', separator = ' ';
• Note the difference between
– a primitive character variable, which holds only one
character, and
– a String object, which can hold multiple characters

Character Sets
• A character set is an ordered list of characters,
with each character corresponding to a unique
number
• A char variable in Java can store any character
from the Unicode character set
• The Unicode character set uses sixteen bits per
character, allowing for 65,536 unique characters
• It is an international character set, containing
symbols and characters from many world
languages

Characters
• The ASCII character set is older and smaller
than Unicode, but is still quite popular
• The ASCII characters are a subset of the
Unicode character set, including:
uppercase letters
lowercase letters
punctuation
digits
special symbols
control characters
A, B, C, …
a, b, c, …
period, semi-colon, …
0, 1, 2, …
&, |, , …
carriage return, tab, ...

Boolean
• A boolean value represents a true or false
condition
• The reserved words true and false are
the only valid values for a boolean type
boolean done = false;
• A boolean variable can also be used to
represent any two states, such as a light bulb
being on or off

IFI7184.DT lesson1- Programming languages

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