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• Module 1 introduces the Java programming language.

History of Java

• James Gosling, Mike Sheridan, and Patrick Naughton initiated the Java project June 1991.
• The team of SUN Microsystems engineers was called Green Team.
• Initially named "Greentalk" by James Gosling with the file extension ".gt".
• Later named Oak, as part of the Green project.
• In 1995, Oak was renamed Java due to a trademark conflict with Oak Technologies.
• The team wanted a name reflecting technology: revolutionary, dynamic, lively, cool, unique, easy to spell/say.
• "Java" was a top choice along with "Silk"; most favored Java for its uniqueness.
• Java is the name of an island in Indonesia where the first coffee (java coffee) was produced, chosen by Gosling while drinking coffee.
• Java is just a name, not an acronym.

Changes and Current State

• Developed by James Gosling at SUN Microsystems, later a subsidiary of Oracle, and released in 1995.
• Time magazine recognized Java as one of the Ten Best Products of 1995.
• Java Development Kit (JDK) 1.0 was released on January 23, 1996.
• Java is used in Windows, Web, enterprise, and mobile applications.
• Java continues to be used in internet programming, mobile devices, games, and e-business solutions..

Motivation

• Java aimed to be a platform-independent language for embedding in consumer electronics.
• One of the first projects was a personal hand-held remote control named Star 7.
• Gosling et al. saw Java's potential for Internet programming as the World Wide Web gained popularity.

Java Technology

• Java is a versatile programming language for creating all kinds of applications.
• Java technology provides tools like:
  • A compiler (javac)
  • An interpreter (java)
  • A documentation generator (javadoc)
  • A class file packaging tool
• Java applications are general-purpose programs running where the Java Runtime Environment (JRE) is installed.
• Two deployment environments include:
  • JRE from Java 2 Software Development Kit (SDK) for class files.
  • Web browsers with a Java technology interpreter and runtime environment.

Features of Java

• Java Virtual Machine (JVM) is an imaginary machine implemented by emulating software to provide hardware platforms to which you compile all Java technology code.
• JVM understands the special machine language called Bytecode.
• Garbage Collection automatically frees memory no longer used during the application's lifetime.
• Code security is implemented through the Java Runtime Environment (JRE).
• JRE runs code compiled for a JVM, performs class loading (via class loader) & code verification by (bytecode verifier) and does code execution.
• Class Loader loads all classes needed for the Java program.
• Bytecode verifier validates the code fragments format and checks for coding that violates access rights to objects.

Java Programs

• Writing includes:
  • Task: Write the program, Tool: Any text editor, Output: File with .java extension
  • Task: Compile the program, Tool: Java compiler, Output: File with .class extension
  • Task: Run the program, Tool: Java interpreter, Output: Program output
• The two types are:
  • Applets: designed to run on a Web browser; small, portable Java programs embedded in HTML pages that provide interactive features.
  • Application programs: Java programs that do not require a Web browser and can be executed on a stand-alone local computer without browsers/internet.

Java Tokens

• Tokens: The smallest individual program unit written in any language, used by the Java compiler for constructing expressions and statements.
• Java's tokens include:
  • Reserved Words/Keywords: Pre-defined words for specific functions.
  • Special Symbols: Characters with special meanings known to the Java compiler that cannot be used for any other purpose.
  • Literals: Similar to normal variables but values cannot be changed; these are constant variables with fixed values.
  • Identifiers: used to name variables, constants, methods, functions, classes, and arrays.
  • Operators: used for arithmetics, logical, and relations

Java Comments

• Java comments are program statements ignored by the compiler and interpreter to make the program readable.
• They allow for easy code maintenance, error finding, information or explanation about the variable, method, class, or any statement.
• Types:
  • Single-line comments: comment on one line of code, using two forward slashes (//).
  • Multi-line comments: comment on multiple lines of code, enclosed between /* and */.
  • Documentation comments: for large programs/software applications to create documentation API, enclosed between /** and */ and using the Javadoc tool.

Quick Review

• Program: sequence of statements intended to accomplish a task.
• Programming: process of planning and creating a program.
• Programming language: set of rules, symbols, and special words used to construct programs.
• Data type: set of values with a set of operations on those values.
• Package: collection of related classes.
• Class: used to create Java programs; basic unit of a Java program; collection of methods and data members.
• Method: set of instructions to accomplish a task; functional element of an object.
• Predefined Methods: nextInt(), print(), nextDouble(), println().
• Java identifier must begin with letter, underscore or dollar sign; must not be a keyword or a reserved word.
• Naming conventions are Pascal case and Camel case.
• PascalCase used in naming Classes while camelCase used in naming variables.
• Errors are bugs; syntax error is a compile-time error, and run-time error is a logical error.