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The history of Java starts with the Green Team. Java team members (also known as Green Team), initiated this project to develop a language for digital devices such as set-top boxes, televisions, etc. However, it was best suited for internet programming. Later, Java technology was incorporated by Netscape.

The principles for creating Java programming were "Simple, Robust, Portable, Platform-independent, Secured, High Performance, Multithreaded, Architecture Neutral, Object-Oriented, Interpreted, and Dynamic". Java was developed by James Gosling, who is known as the father of Java, in 1995. James Gosling and his team members started the project in the early '90s.

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James Gosling, Mike Sheridan, and Patrick Naughton initiated the Java language project in June 1991. The small team of sun engineers called Green Team.

Initially it was designed for small, embedded systems in electronic appliances like set-top boxes.

Firstly, it was called "Greentalk" by James Gosling, and the file extension was .gt.

After that, it was called Oak and was developed as a part of the Green project. Oak is a symbol of strength and chosen as a national tree of many countries like the U.S.A., France, Germany, Romania, etc.

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In 1995, Oak was renamed as "Java" because it was already a trademark by Oak Technologies.

The team gathered to choose a new name. The suggested words were "dynamic", "revolutionary", "Silk", "jolt", "DNA", etc. They wanted something that reflected the essence of the technology: revolutionary, dynamic, lively, cool, unique, and easy to spell, and fun to say.

According to James Gosling, "Java was one of the top choices along with Silk". Since Java was so unique, most of the team members preferred Java than other names.

Java is an island in Indonesia where the first coffee was produced (called Java coffee). It is a kind of espresso bean. Java name was chosen by James Gosling while having a cup of coffee nearby his office.

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Java Version History

JDK Alpha and Beta (1995)

JDK 1.0 (23rd Jan 1996)

JDK 1.1 (19th Feb 1997)

J2SE 1.2 (8th Dec 1998)

J2SE 1.3 (8th May 2000)

J2SE 1.4 (6th Feb 2002)

J2SE 5.0 (30th Sep 2004)

Java SE 6 (11th Dec 2006)

Java SE 7 (28th July 2011)

Java SE 8 (18th Mar 2014)

Java SE 9 (21st Sep 2017)

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Java SE 10 (20th Mar 2018)

Java SE 11 (September 2018)

Java SE 12 (March 2019)

Java SE 13 (September 2019)

Java SE 14 (Mar 2020)

Java SE 15 (September 2020)

Java SE 16 (Mar 2021)

Java SE 17 (September 2021)

Java SE 18 March 2022)

Java SE 19 (2023)

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Top 10 Java IDE

IntelliJ IDEA
Eclipse
Apache NetBeans
MyEclipse IDE
BlueJ IDE
Xcode IDE
Jdeveloper IDE
JCreator IDE
DrJava IDE
Greenfoot IDE

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What is Bytecode in Java?

Can you imagine a world where we have to write code multiple times for each device with varying specifications like operating system, processor architecture, etc.? It will be a tedious process. Keeping these things in mind, Java developers came up with the concept of Write Once Read Anywhere, which got incorporated as a feature in the Java language. To achieve this, a code known as bytecode gets generated after compiling our Java source code. We will now discuss the same.

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Bytecode in Java is a set of instructions for the Java Virtual Machine. Java Virtual Machine, abbreviated as JVM, enables a computer to run code written in Java. When a Java program is compiled, the bytecode gets generated. It is equivalent to the assembler in C++.

Bytecode is a platform-independent set of instructions primarily because it is interpreted and executed by the JVM. Code that runs on multiple computer architectures without any modification is called machine or platform-independent code.

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How Java Works

Java's platform independence is achieved by the use of the Java Virtual Machine
A Java program consists of one or more files with a .java extension

these are plain old text files

When a Java program is compiled the .java files are fed to a compiler which produces a .class file for each .java file
The .class file contains Java bytecode.
Bytecode is like machine language, but it is intended for the Java Virtual Machine not a specific chip such as a Pentium or PowerPC chip

Java Basics

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A Picture is Worth…

Java Basics

The Interpreter is sometimes referred to as the Java Virtual Machine

The output of the compiler is .class file

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So What!

The platform independence of Java may be a huge marketing tool, but is actually of little use to people learning Object Oriented Programming and Abstract Data Types
What is of use is the simplicity of the Java syntax and programming concepts
Java is a "pure" Object Oriented Language

encapsulation, inheritance, and polymorphism
all code must be contained in a class
no free functions (functions that do not belong to some class) like C++, although someone who wants to write messy Java code certainly can
Is OO the best programming paradigm?

Java Basics

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HelloWorld.java

Java Basics

/**

* A simple program

public class HelloWorld

{

public static void main(String[] args)

{

System.out.println("HELLO World!");

}

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Java Language�Review of Basic Features

Java Basics

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Basic Features

Identifiers
Data Types

primitives
classes / objects

Expressions and operators
Control Structures
Arrays
Methods
Programming for correctness

pre and post conditions
assertions

Java Basics

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Identifiers in Java

letters, digits, _, and $ (don't use $. Can confuse the runtime system)
start with letter, _, or $
by convention:

start with a letter
variables and method names, lowercase with internal words capitalized e.g. honkingBigVariableName
constants all caps with _ between internal words e.g. ANOTHER_HONKING_BIG_INDENTIFIER
classes start with capital letter, internal words capitalized, all other lowercase e.g HonkingLongClassName

Why? To differentiate identifiers that refer to classes from those that refer to variables

Java Basics

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Java Data Types

Java Basics

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Data Types

Primitive Data Types

byte short int long float double boolean char

��

stick with int for integers, double for real numbers

Classes and Objects

pre defined or user defined data types consisting of constructors, methods, and fields (constants and fields (variables) which may be primitives or objects.)

Java Basics

//dataType identifier;

int x;

int y = 10;

int z, zz;

double a = 12.0;

boolean done = false, prime = true;

char mi = 'D';

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Java Primitive Data Types

Java Basics

Data Type	Characteristics	Range
byte	8 bit signed integer	-128 to 127
short	16 bit signed integer	-32768 to 32767
int	32 bit signed integer	-2,147,483,648 to 2,147,483,647
long	64 bit signed integer	-9,223,372,036,854,775,808 to- 9,223,372,036,854,775,807
float	32 bit floating point number	+ 1.4E-45 to�+ 3.4028235E+38
double	64 bit floating point number	+ 4.9E-324 to�+ 1.7976931348623157E+308
boolean	true or false	NA, note Java booleans cannot be converted to or from other types
char	16 bit, Unicode	Unicode character, \u0000 to \uFFFF Can mix with integer types

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What are Classes and Objects?

Class is synonymous with data type
Object is like a variable

The data type of the Object is some Class
referred to as an instance of a Class

Classes contain:

the implementation details of the data type
and the interface for programmers who just want to use the data type

Objects are complex variables

usually multiple pieces of internal data
various behaviors carried out via methods

Java Basics

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Creating and Using Objects

Declaration - DataType identifier

Rectangle r1;

Creation - new operator and specified constructor

r1 = new Rectangle();

Rectangle r2 = new Rectangle();

Behavior - via the dot operator

r2.setSize(10, 20);

String s2 = r2.toString();

Refer to documentation for available behaviors (methods)

Java Basics

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Built in Classes

Java has a large built in library of classes with lots of useful methods

Ones you should become familiar with quickly

String
Math
Integer, Character, Double

System
Arrays
Scanner
File
Object
Random
For rest of the classes look at the Java API page

Java Basics

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import

import is a reserved word
packages and classes can be imported to another class
does not actually import the code (unlike the C++ include preprocessor command)
statement outside the class block�import java.util.ArrayList;�import java.awt.Rectangle;�public class Abc{� // code for class Abc�}�

Java Basics

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The String Class

String is a standard Java class

a whole host of behaviors via methods

also special (because it used so much)

String literals exist (no other class has literals)�String name = "Mike D.";
String concatenation through the + operator�String firstName = "Mike";�String lastName = "Scott";�String wholeName = firstName + lastName;
Any primitive or object on other side of + operator from a String automatically converted to String

Java Basics

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Standard Output

To print to standard output use

System.out.print( expression ); // no newline

System.out.println( expression ); // newline

System.out.println( ); // just a newline

common idiom is to build up expression to be printed out

System.out.println( "x is: " + x + " y is: " + y );

Java Basics

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Constants

Literal constants - "the way you specify values that are not computed and recomputed, but remain, well, constant for the life of a program."

true, false, null, 'c', "C++", 12, -12, 12.12345

Named constants

use the keyword final to specify a constant
scope may be local to a method or to a class

By convention any numerical constant besides -1, 0, 1, or 2 requires a named constant

final int NUM_SECTIONS = 3;

Java Basics

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Expressions and Operators

Java Basics

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Operators

Basic Assignment: =
Arithmetic Operators: +, -, *, /, %(remainder)

integer, floating point, and mixed arithmetic and expressions

Assignment Operators: +=, -=, *=, /=, %=
increment and decrement operators: ++, --

prefix and postfix.
avoid use inside expressions.

int x = 3;�x++;

Java Basics

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Expressions

Expressions are evaluated based on the precedence of operators
Java will automatically convert numerical primitive data types but results are sometimes surprising

take care when mixing integer and floating point numbers in expressions

The meaning of an operator is determined by its operands

is it integer division or floating point division?

Java Basics

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Casting

Casting is the temporary conversion of a variable from its original data type to some other data type.

Like being cast for a part in a play or movie

With primitive data types if a cast is necessary from a less inclusive data type to a more inclusive data type it is done automatically.

int x = 5;�double a = 3.5;�double b = a * x + a / x;�double c = x / 2;

if a cast is necessary from a more inclusive to a less inclusive data type the class must be done explicitly by the programmer

failure to do so results in a compile error.�double a = 3.5, b = 2.7;�int y = (int) a / (int) b;�y = (int)( a / b );�y = (int) a / b; //syntax error

Java Basics

CS 307 Fundamentals of Computer Science

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Primitive Casting

Java Basics

CS 307 Fundamentals of Computer Science

double

float

long

int

short,�char

byte

Outer ring is most�inclusive data type.�Inner ring is least

inclusive. ��In expressions

variables and

sub expressions

of less inclusive

data types are

automatically cast

to more inclusive.�

If trying to place

expression that is

more inclusive into

variable that is less

inclusive, explicit cast

must be performed.

From MORE to LESS

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Java Control Structures

Java Basics

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Control Structures

linear flow of control

statements executed in consecutive order

Decision making with if - else statements

if(boolean-expression)� statement;�if(boolean-expression)�{ statement1;� statement2;� statement3;�}�A single statement could be replaced by a statement block, braces with 0 or more statements inside

Java Basics

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Boolean Expressions

boolean expressions evaluate to true or false
Relational Operators: >, >=, <, <=, ==, !=
Logical Operators: &&, ||, !

&& and || cause short circuit evaluation
if the first part of p && q is false then q is not evaluated
if the first part of p || q is true then q is not evaluated

//example�if( x <= X_LIMIT && y <= Y_LIMIT)� //do something

Java Basics

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More Flow of Control

if-else:�if(boolean-expression)� statement1;�else� statement2;
multiway selection:�if(boolean-expression1)� statement1;�else if(boolean-expression2)� statement2;�else� statement3;
individual statements could be replaced by a statement block, a set of braces with 0 or more statements
Java also has the switch statement, but not part of our subset

Java Basics

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for Loops

for loops�for(init-expr;boolean-expr;incr-expr)� statement;
init-expr and incr-expr can be more zero or more expressions or statements separated by commas
statement could be replaced by a statement block

Java Basics

execute� init-expr

evaluate �boolean-expr

false

skip to 1^st statement after�body of loop

true

execute�body of loop

execute�incr-expr

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while loops

while loops�while(boolean-expression)� statement; //or statement block
do-while loop part of language�do� statement;�while(boolean-expression);
Again, could use a statement block
break, continue, and labeled breaks

referred to in the Java tutorial as branching statements
keywords to override normal loop logic
use them judiciously (which means not much)

Java Basics

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Enhanced for loop

New in Java 5.0
Also known as the for-each loop
useful short hand for accessing all elements in an array (or other types of structures) if no need to alter values
alternative for iterating through a set of values

for(Type loop-variable : set-expression)

statement

logic error (not a syntax error) if try to modify an element in array via enhanced for loop

Java Basics

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Enhanced for loop

Java Basics

public static int sumListEnhanced(int[] list)

{ int total = 0;

for(int val : list)

{ total += val;

System.out.println( val );

}

return total;

}

public static int sumListOld(int[] list)

{ int total = 0;

for(int i = 0; i < list.length; i++)

{ total += list[i];

System.out.println( list[i] );

}

return total;

}