Java 101 Intro to Java Programming

Java 101: Intro to Java
Programming

Introduction
• Your Name
• Your day job
• Your last holiday destination?

Java 101
• Java Fundamentals
– Setting up your development environment
– Language Overview
– How Java Works
– Writing your first program
– Built-in Data Types
– Conditionals and Loops

Java 102
• Object-oriented Programming
– Classes and Objects
– Polymorphism, Inheritance and Encapsulation
– Functions and Libraries

Java 103
• Data Structures
– Arrays
– Collections
– Algorithms

Java 101: Introduction to Java
Setting up your Development
Environment

Installing Java Development Kit
• Download latest Java SE 8 JDK (not JRE) from
http://www.oracle.com/technetwork/java/javase/downloads/jdk8-
downloads-2133151.html
• For Windows,
– download the X86 version, double click the .exe file and follow the
instructions, accepting all default
• For MACs,
– check if java already installed (javac –version) and if not, download the
JDK dmg file, run it and follow the instructions.
• After installation is complete, type javac –version in the Command
window (Terminal window on MAC OS)-
– The reported version should be 1.8....
– If not, you may need to modify the system variable PATH to include the
bin directory of JDK

What is an IDE?
• IDE = Integrated Development Environment
• Makes you more productive
• Includes text editor, compiler, debugger,
context- sensitive help, works with different
Java SDKs
• Eclipse is the most widely used IDE
• Alternatives:
– IntelliJ IDEA (JetBrains)
– NetBeans (Oracle)

Installing Eclipse
• Download and install the latest Eclipse for Java
EE (32 Bit version) from
http://www.eclipse.org/downloads
• Unzip the content of the archive file you
downloaded
• To start Eclipse
– On PC, double-click on Eclipse.exe
– On Mac, double click Eclipse.app in Application
folder

Hands-on Exercise
Eclipse Setup & Demo

Language Overview

Java Language Overview
• Object-oriented
• Statically typed
• Widely available
• Widely used

Java Versions
• Brief History…
– 1990 : Small team at Sun
Microsystems start work on
C/C++ replacement
• Major Version Releases
– JDK 1.0 (January 21, 1996)
– JDK 1.1 (February 19, 1997)
– J2SE 1.2 (December 8, 1998)
– J2SE 1.3 (May 8, 2000)
– J2SE 1.4 (February 6, 2002)
– J2SE 5.0 (September 30, 2004)
– Java SE 6 (December 11, 2006)
– Java SE 7 (July 28, 2011)
– Java SE 8 (March 18, 2014)

Java Editions
• Java SE: Java Standard Edition
• Java EE: Java Enterprise Edition (a.k.a. J2EE)
– includes a set of technologies built on top of Java
SE: Servlets, JSP, JSF, EJB, JMS, et al.
• Java ME: Java Micro Edition
• Java Card for Smart Cards
• All Java programs run inside the Java Virtual
Machine (JVM)

JDK vs. JRE
• Java Development Kit (JDK) is required to
develop and compile programs
• Java Runtime Environment (JRE) is required to
run programs.
• Users must have JRE installed,
• Developers must have the JDK installed
• JDK includes the JRE

How Java Works

Writing Your First Program

Writing Your First Java Program
• Create a new project in your IDE named Java101
• Create a HelloWorld class in the src folder inside the Java101
project as illustrated below.

Compiling Your First Java Program
• Save the HelloWorld class in the IDE
• This automatically compiles the HelloWorld.java file
into into a HelloWorld.class file
• Go to the folder you created the Java101 project on
your hard disk and open the src folder.
• What do you see?

Running Your First Java Program
• Run your program in Eclipse by right-clicking
and selecting Run As>Java Application.

Java 101 Intro to Java Programming

Anatomy of a Java Application
Comments Class Name
Access
modifier
Function/static
method
Arguments

Introduction to Java
Built-in Data Types

Built-in Data Types
• Data type are sets of values and operations
defined on those values.

Basic Definitions
• Variable - a name that refers to a value.
• Assignment statement - associates a value
with a variable.

String Data Type
Data Type Attributes
Values sequence of characters
Typical literals “Hello”, “1 “, “*”
Operation Concatenate
Operator +
• Useful for program input and output.

String Data Type
• Meaning of characters depends on context.

String Data Type
Expression Value
“Hi, “ + “Bob” “Hi, Bob”
“1” + “ 2 “ + “ 1” “ 1 2 1”
“1234” + “ + “ + “99” “1234 + 99”
“1234” + “99” “123499”

Hands-on Exercise
Command Line Arguments

Exercise: Command Line Arguments
• Create the Java program below that takes a name as command-line
argument and prints “Hi <name>, How are you?”

Integer Data Type
Values Integers between -2E31 to +2E31-1
Typical literals 1234, -99 , 99, 0, 1000000
Operation Add subtract multiply divide remainder
Operator + - * / %
• Useful for expressing algorithms.

Integer Data Type
Expression Value Comment
5 + 3 8
5 – 3 2
5 * 3 15
5 / 3 1 no fractional
part
5 % 3 2 remainder
1 / 0 run-time error
3 * 5 - 2 13 * has
precedence
3 + 5 / 2 5 / has
precedence
3 – 5 - 2 -4 left associative
(3-5) - 2 -4 better style
3 – (5-2) 0 unambiguous

Double Data Type
• Useful in scientific applications and floating-
point arithmetic
Values Real numbers specified by the IEEE 754 standard
Typical literals 3.14159 6.022e23 -3.0 2.0 1.41421356237209
Operation Add subtract multiply divide
Operator + - * /

Double Data Type
Expression Value
3.141 + 0.03 3.171
3.141 – 0.03 3.111
6.02e23 / 2 3.01e23
5.0 / 2.0 1.6666666666667
10.0 % 3.141 0.577
1.0 / 0.0 Infinity
Math.sqrt(2.0) 1.4142135623730951

Java Math Library
Methods
Math.sin() Math.cos()
Math.log() Math.exp()
Math.sqrt() Math.pow()
Math.min() Math.max()
Math.abs() Math.PI
http://java.sun.com/javase/6/docs/api/java/lang/Math.html

Hands-on Exercise
Integer Operations

Exercise: Integer Operations
• Create a Java class named IntOpsin the Java101 project that performs integer
operations on a pair of integers from the command line and prints the results.

Boolean Data Type
• Useful to control logic and flow of a program.
Values true or false
Typical literals true false
Operation and or not
Operator && || !

Truth-table of Boolean Operations
a !a a b a && b a || b
true false false false false false
false true false true false true
true false false true
true true true true

Boolean Comparisons
• Take operands of one type and produce an
operand of type boolean.
operation meaning true false
== equals 2 == 2 2 == 3
!= Not equals 3 != 2 2 != 2
< Less than 2 < 13 2 < 2
<= Less than or
equal
2 <= 2 3 <= 2
> Greater than 13 > 2 2 > 13
>= Greater than
or equal
3 >= 2 2 >= 3

Type Conversion
• Convert from one type of data to another.
• Implicit
– no loss of precision
– with strings
• Explicit:
– cast
– method.

Type Conversion Examples
expression Expression type Expression value
“1234” + 99 String “123499”
Integer.parseInt(“123”) int 123
(int) 2.71828 int 2
Math.round(2.71828) long 3
(int) Math.round(2.71828) int 3
(int) Math.round(3.14159) int 3
11 * 0.3 double 3.3
(int) 11 * 0.3 double 3.3
11 * (int) 0.3 int 0
(int) (11 * 0.3) int 3

Hands-on Exercise
Leap Year Finder

Exercise: Leap Year Finder
• A year is a leap year if it is either divisible by 400
or divisible by 4 but not 100.
• Write a java class named LeapYear in the Java101
project that takes a numeric year as command
line argument and prints true if it’s a leap year
and false if not

Data Types Summary
• A data type is a set of values and operations on those
values.
– String for text processing
– double, int for mathematical calculation
– boolean for decision making
• In Java, you must:
– Declare type of values.
– Convert between types when necessary
• Why do we need types?
– Type conversion must be done at some level.
– Compiler can help do it correctly.
– Example: in 1996, Ariane 5 rocket exploded after takeoff
because of bad type conversion.

Introduction to Java
Conditionals and Loops

Conditionals and Loops
• Sequence of statements that are actually
executed in a program.
• Enable us to choreograph control flow.

Conditionals
• The if statement is a common branching structure.
– Evaluate a boolean expression.
• If true, execute some statements.
• If false, execute other statements.

While Loop
• A common repetition structure.
– If true, execute some statements.
– Repeat.

For Loop
• Another common repetition structure.
– Execute initialization statement.
• If true, execute some statements.
– And then the increment statement.
– Repeat.

Hands-on Exercise
Powers of Two

Exercise: Powers of Two
• Create a new Java project in Eclipse named Pow2
• Write a java class named PowerOfTwo to print powers of 2 that are
<= 2N where N is a number passed as an argument to the program.
– Increment i from 0 to N.
– Double v each time

Control Flow Summary
• Sequence of statements that are actually
executed in a program.
• Conditionals and loops enable us to choreograph
the control flow.
Control flow Description Example
Straight line
programs
all statements are executed in the
order given
Conditionals certain statements are executed
depending on the values of certain
variables
If
If-else
Loops certain statements are executed
repeatedly until certain conditions
are met
while
for
do-while

Homework Exercises

Hands-on Exercise
Random Number Generator

Exercise: Random Number Generator
• Write a java class named RandomInt to generate a
pseudo-random number between 0 and N-1 where N is
a number passed as an argument to the program

Solution: Random Number Generator

Hands-on Exercise
Array of Days

Exercise: Array of Days
• Create a java class named DayPrinter that
prints out names of the days in a week from an
array using a for-loop.

Solution: Arrays of Days
public class DayPrinter {
public static void main(String[] args) {
//initialize the array with the names of days of the
week
String[] daysOfTheWeek =
{"Sunday","Monday","Tuesday","Wednesday",
"Thuesday","Friday”,"Saturday"};
//loop through the array and print their elements to
//stdout
for (int i= 0;i < daysOfTheWeek.length;i++ ){
System.out.println(daysOfTheWeek[i]);
}
}
}
% javac DayPrinter.java
% java DayPrinter
Sunday
Monday
Tuesday
Wednesday
Thuesday
Friday
Saturday

Hands-on Exercise
Print Personal Details

Exercise: Print Personal Details
• Write a program that will print your name and
address to the console, for example:
Alex Johnson
23 Main Street
New York, NY 10001 USA

Hands-on Exercise
Sales Discount

Exercise: Sales Discount
• Create a new project in Eclipse named Sale
• Create, compile, and run the FriendsAndFamily class as illustrated below
• Debug this program in your IDE to find out how it works

Further Reading
• Java Tutorials - https://docs.oracle.com/javase/tutorial/
• Java Language Basics -
http://docs.oracle.com/javase/tutorial/java/nutsandbolts/index.html
• Eclipse IDE Workbench User Guide -
http://help.eclipse.org/kepler/index.jsp
• Eclipse Tutorial - http://www.vogella.com/tutorials/Eclipse/article.html

Java 101 Intro to Java Programming

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