Download Fundemental Programming Structures in Java (Chapter 3)

Introduction to Java
Tavaris J. Thomas Ph.D.
BNAI ZION SCIENTISTS DIVISION
JOB ORIENTATION & TERMINOLOGY CLASSES
Fall 2012
Contact Info
• Tavaris J. Thomas
– [email protected]
– www.ee.cooper.edu/~tthomas/java
• Google Group
– http://groups.google.com/group/bz-java
Any Programming Experience?
Class Logistics
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Lectures will run every Tues 6:00pm – 9:00pm
The Cooper Union Microlab 602
Approx 4+ programming assignments.
Class Lectures will be available on the class group
page or on the class webpage
• Textbook:
– Core Java ,Volume 1 – Fundamentals (8th edition)
– Cay S. Horstmann and Gary Cornel
– ISBN: 0132354764
Course Topics
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Introduction to Java
Fundamentals
Objects and Classes
Inheritance
Interfaces and Inner Classes
Deploying Applications
Debugging and Exceptions
Multithreading
Week 1
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Introduction
What is Java?
Installing the Java SDK and Eclipse IDE
Language Fundamentals
History of Java
• Began as a Sun Microsystems project called
“Green”
• James Gosling
• Intended to be used on a variety of architectures
• All code is translated to the same “Virtual
Machine” code, and specific interpreters are
written for the VM
• Chose to make it object-oriented like C++ instead
of like Pascal
• First commercial application: applets (1995)
Java’s Evolution
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Java 1.0 First release
Java 1.1 Inner classes
Java 1.2-1.3 (no additions)
Java 1.4 Assertions
Java 5.0 [“1.5”] Generic classes, for each loops, variable
arguments, autoboxing, metadata, enums, static import
• Java 6 Performance improvements, library enhancements
update 37
• Java 7 More security and library enhancements – update 9
• Java 8 TDA September 2013
Versions of Java
• Java SE – Standard Edition
• Java ME – Micro Edition – embedded devices
or resource constrained devices – set top
boxes, blu-ray players, mobile devices
• Java EE – Enterprise Edition – For server side
processing
Uses of Java
• “Write Once, Run Anywhere”
– Stand alone applications
– Applets (java code embedded into webpages run
via we browser)
– Servlets (server side Java code that interact with
clients typically using HTTP)
• Android development
Programming Languages
• Interpreted languages
– Perl
– Python
– PHP
• Compiled languages
– BASIC
– C/C++
– Fortran
– Java (to bytecode)
JVM Approach
• Architecture neutral
– Only need an implementation of JVM for the native
machine
– Same Java code will run on all platforms
• Portable
– The results on x86 = results on ARM = results on PPC
– Caveat: don’t always fully utilize architecture capabilities
• Object oriented
– Everything is a class
• Doesn’t this all mean Java is slow?
– On average: slower than compiled languages
– But, using just-in-time (JIT) compiler Java is fast!
Grabbing Java and Eclipse
1. Go to
http://www.oracle.com/technetwork/java/javase/do
wnloads/index.html
2. Download Java SE 6 Update 37 JDK (includes the JRE)
3. Install the JDK
4. Install the JRE
5. Download Eclipse from:
http://www.eclipse.org/downloads/packages/eclipse-idejava-developers/heliossr2
6. Continue with installing Eclipse IDE
Hello World Example
• Simplest possible program: prints one line
• Will re-visit this program later
public class HiWorld {
public static void main(String[] args) {
System.out.println(“Hello World“);
}
}
Another Example
• Uses an array of three strings and a loop
public class Greetings {
public static void main(String[] args) {
String[] greeting = new String[3];
greeting[0] = "Welcome to BNAI ZION";
greeting[1] = “Introduction to Java";
greeting[2] = “Spring 2012 ";
for(String thisline : greeting)
System.out.println(thisline);
}
}
“Hello World” In-depth
public class HiWorld {
public static void main(String[] args) {
// this is a comment.
/* so is this, but the following is
a statement: */
System.out.println(“Hello World“);
}
}
•Java is case sensitive
•public is an access modifier
•Controls level of access other part of program have to this code
•Everything in Java is a class – used to create building blocks
•System.out is an object, calling its println method with parameter “Hello World”
Class
• Class is a container for the program logic that
defines the behavior of an application
• Building blocks with which all Java applications
and applets are built.
• Everything in a Java program must be inside a
class.
• Following the keyword class is the name of the
class.
• Names must begin with a letter, and after that,
they can have any combination of letters and
digits.
Simple Template with Javadoc
/**
* This is a simple template, documented.
* @version 0.01
* @author Your Name
*/
public class ClassName{
public static void main(String[] args){
program statements;
}
}
The 8 Primitive Data Types in Java
Variables
• For any meaningful program you need to modify data
• Variables are used to store values
• Operators operate on one or two variables
– Forming expressions
• Declare a variable called Name of type type:
– type Name;
– Example:
• String name;
int a, b;
• Assigning Name a value val:
– type Name=val;
– Example:
• String name=“Don Knuth”;
int a=3;
float k=3.3;
Integer Types
• Range depends on size of each type:
– long (8 bytes) -9,223,372,036,854,775,808 to
9,223,372,036,854,775,807
– int (4 bytes) -2,147,483,648 to 2,147,483,647
– short (2 bytes) -32,768 to 32,767
– byte (1 byte) -128 to 127
• All integer types are signed (the unsigned
keyword does not exist in Java)
• All integer types are the same size regardless of
the device’s architecture
Representing Floating Point
• Used for positive and negative numbers with
fractional parts
– Range and precision both depend on type
– float (4 bytes) ±3.40282347*1038
– double (8 bytes) ±1.79769313486231570*10308
• Float stores up to 7 fractional digits
• Double stores 15 decimal digits
– In general, doubles should be used instead of Float
– If speed or memory are constrained, floats may be
necessary
Representing Characters
• Unlike C, where char is almost always a single
byte, a Java char can hold a multi-byte Unicode
character
• Every char is 16 bits (2 bytes), and stores either a
complete character of Unicode U+0000 to U+FFFF
or half of a U+10000 to U+10FFFF character
• In most cases, String variable should be used to
avoid having to worry about character types and
lengths.
– String pi = "\u03C0”;
//π
Boolean Types
• Can only indicate two values , true or false
• Unlike C/C++, integer 0 and 1 are not equivalent to
false and true
• Avoid easy-to-create bugs. For example:
if((x=1)) {
statement;
} //this would not compile in Java
• Must use true and false when assigning boolean
variables
• No implicit conversion is possible between boolean
and other data types
Strings
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Java does NOT have a built-in string type
Standard library contains class called String
Every quoted string is an instance of this class
Java strings are sequence of Unicode
characters
– Example: “Java\u2122” consists of: J,a,v,a,™
– Example: String e = “”; //an empty string
– String planet = “Earth”;
• More later with String API
Enumerated Types
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Sometimes variable should only hold a value
from specific (restricted) set
Example:
Shirt size allowed to be small, medium, large
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You can, of course do:
int SMALL=1;
int MEDIUM=2;
int LARGE=3;
int shirtSize=one-of-the-above;
• But nothing prevents one from setting shirtSize=-1;
– Solution: enum’s:
– Enum Size {SMALL, MEDIUM, LARGE};
• Size shirtSize=Size.one-of-the-above;