Java Programming Concepts

• At the end of the lesson, the learner will be able to identify and learn: Reserved Words, Identifiers, Data Types, Operators, Assignment Statements, Expressions, Class String, Packages, Classes, Methods, and the Import statement.

Introduction to Java

• Java is an object-oriented language used for web-based internet and general-purpose programs
• Key attributes are security features and architectural neutrality (platform independent)
• Java started as the programming language Oak
• The Green Project members, James Gosling, Patrick Naughton, and Mike Sheridan, developed Oak in 1991
• Sun Microsystems' chief programmer, James Gosling, was tasked to create software for controlling consumer electronic devices
• The team aimed for a new way of computing based on network power that could operate on different computer platforms
• Due to patenting issues, Oak was renamed Java

Characteristics of Java

• Simple and easy to learn
• Object-oriented with classes and objects, featuring abstraction, encapsulation, polymorphism, and inheritance
• Distributed, allowing Java programs to access data across a network
• Code is compiled to bytecode and interpreted when executed
• Robust, making programs less prone to errors
• Architecture neutral and portable; bytecode runs on various operating systems
• Secure, preventing programmers from manipulating system memory
• A high-performance language, faster than other interpreter-based languages
• Multithreaded, enabling simultaneous execution of program parts
• Dynamic, facilitating easy maintenance of different application versions

Java Program Types

• Applets can be written, which are programs embedded in a Web Page.
• Servlets extend the functionality of Web servers.
• Java Applications are stand-alone programs
• Java Applications have two subdivisions:
• Console applications, supporting character or text output to a computer screen
• Windowed Applications, creating a GUI with such elements as menus, toolbars, and dialog boxes

Java Identifier

• A Java identifier must begin with a letter of the English alphabet, a non-English letter, an underscore, or a dollar sign
• Class names may not start with a digit.
• A Java identifier consists of letters, digits, underscores (_), or dollar signs ($)
• It cannot be a reserved keyword like public or class
• Java identifier must not use true, false, or null as they are reserved
• Variable: a named memory location to store a value.
• Variables can hold only one value, but the value can be changed
• Data type: describes the data type stored, the memory used, and the operations allowed
• Java provides eight primitive data types

Declaring Variables

• Datatype + identifier + assignment operator (optional) + an ending semicolon (;)
• Example: int myAge = 25;

Java Identifier - Constant

• Constant has an unchangeable value while a program is running
• For example, System.out.println(459); includes the constant 459
• Programmers refer to the 459 as a literal constant since its value is taken literally each use
• The number 459 is also a numeric constant as opposed to a character or string constant
• It is an unnamed constant as opposed to a named one, because no identifier is associated with it.

Declaring Constants

• A named constant differs from a variable, as it uses the keyword final
• Assign a value only once, it can never be changed
• Named constants are typically initialized when declared; if not, it's a blank final
• Conventionally given identifiers in all uppercase with underscores to separate words
• For example: final int NUMBER_OF_DEPTS = 20;

Java Keywords

• Consist of words in the Java programming language, like abstract, continue, etc
• Keywords like const and goto are reserved, but are not currently in use
• Values true, false, and null are literals but cannot be used as identifiers

Java Data Types

• Classified in two types:
• Primitive/Standard
• Abstract/Derived

Java Data Types - Primitive

• Built into the Java language
• The Java compiler contains detailed instructions on each legal operation supported by the data type.
• The eight primitive data types: byte, short, int, long, float, double, char, and Boolean
• Byte is 8-bit, a byte-length integer with a range of -128 to +127.
• Short is 16-bit, a short integer with a range of -32768 to +32767.
• Int is 32-bit, an integer with a range of -231 to 231 - 1.
• Long is 64-bit, a long integer with a range of -263 to 263 - 1.
• Float is 32-bit, single-precision floating point with a range of +/- about 1039.
• Double is 64-bit, double-precision floating point with a range of +/- about 10317.
• Char is 16-bit, representing a single character.
• Boolean is 1-bit, representing a boolean value (true or false).

Java Data Types - Abstract

• Based on primitive types, having more functionality
• The String data type can store letters, digits, and other characters, such as /, () : ; $ and #
• Cannot perform calculations on a string variable, even if it has digits
• String provides methods for concatenating, searching, and extracting
• Primitive data types don't have these features

Java Operators

• Arithmetic
• Assignment
• Unary
• Comparison
• Logical
• Conditional
• New

Java Operators - Arithmetic:

• Operator (+) performs addition, adding values and storing the result.
• Operator (-) performs subtraction.
• Operator (*) performs multiplication.
• Operator (/) performs division.
• Operator (%) performs modulo, dividing and storing the remainder.

Java Operators - Assignment

• (=): Assigns the right operand's value to the left.
• (+=): Adds operands, assigns the result left.
• (-=): Subtracts right operand, stores the result left.
• (*=): Multiplies operands, stores the result left.
• (/=): Divides operands, stores the result left.
• (%=): Divides left operand, stores the remainder left.

Java Operators - Unary

• (++) increments the value of operand by one (=operand + 1)
• (--) decrements value of operand by one (=operand - 1)
• Increment and decrement operators have two uses: prefix and postfix

Java Operators - Comparison

• (==) Evaluates if the operands are equal
• (!=) Evaluates if the operands are not equal
• (>) Evaluates if the left operand is greater than the right
• (<) Evaluates if the left operand is less than the right
• (>=) Evaluates if the left operand is greater than/equal to the right

Java Operators - Logical

• (&&) Evaluates if both evaluate to be true
• (||) Evaluates to true if at least one of the conditions evaluate to be true

Java Operators - Conditional

• (condition ? true_val : false_val) Evaluates to true_val if the condition returns true and false_val if the condition returns false

Java Operators - New

• Allocates memory for a class instance, requiring the new operator
• Declaring an object simply states the data type
• Syntax: <class_name><object_name> = new <class_name>();

This lesson covers fundamental Java concepts, including servlets, identifiers, primitive data types, and memory management. It also addresses Java's platform independence and object-oriented paradigm. Key figures like James Gosling and important features like multithreading are discussed.