Overview of Programming and Java

Main Components of a computer

• CPU - Central Processing Unit: The "brain" of the computer
  • ISA - Instruction Set Architecture: the specific set of low-level instructions available to a CPU. Differs for various CPU types (Intel Pentium, Mac G4, etc)
• ALU - Arithmetic & Logic Unit
  • responsible for performing arithmetic calculations, as well as logical operations (comparisons for equality, inequality, for instance).
• Main Memory (RAM - Random Access Memory)
  • storage close to CPU
  • Faster to access than hard disk
  • stores executing programs and data being currently worked on
• Secondary Memory
  • hard disk, floppy disk, CD, DVD, etc.
• Input devices
  • mouse, keyboard, scanner, network card, etc.
• Output devices
  • screen/console, printer, network card, etc.
• Operating System
  • Examples: Mac OS, Windows XP, Linux
  • Controls computer operations
  • Manages allocation of resources for currently running applications

Memory Concepts

• bit: a binary digit
  • Stores the value 0 or 1
  • Smallest unit of storage in a computer
• byte: 8 bits
  • Smallest addressable unit of storage in a computer
  • Storage units (variables) in a program are 1 or more bytes
  • Each byte in memory has an address (a number that identifies the location)

Programming, and Programming Languages

• Program - a set of instructions for a computer to execute
• Evolution of Programming languages
  • Machine Language
    • Based on machine's core instruction set
    • Needed by computer, hard for humans to read (1's and 0's)
    • Example: 1110110101010110001101010
      • Say what?
  • Assembly Language
    • translation of machine instructions to symbols, slightly easier for humans to read
    • Example: ADD $R1, $R2, $R3
      • Well, we know it has something to do with addition!
  • High-level procedural languages
    • Abstraction of concepts into more human-readable terms
    • Closer to "natural language" (i.e. what we speak)
    • Easy to write and design, but must be translated for computer
    • Examples include C, Pascal, Fortran
  • Object-oriented languages
    • Abstraction taken farther than procedural languages
    • Objects model real-world objects, not only storing data (attributes), but having inherent behaviors (operations, functions)
    • Easier to design and write good, portable, maintainable code
    • Examples include Smalltalk, C++, Java
• Bridging the gap between high-level code and machine code
  • Interpreted languages -- source code is directly run on an interpreter, a program that runs the code statements
  • Compiled Languages
    • A compiler program translates source code (what the programmer writes) to machine language (object code)
    • A linker program puts various object code files together into an executable program (or other target type, like a DLL)
    • C and C++ are compiled languages
  • Java is a mix of both!

Building Programs

Software development

• Analysis and problem definition
• Design - includes design of program or system structure, algorithms, user-interfaces, and more
• Implementation (coding)
• Testing - can be done during design, during implementation, and after implementation
• Maintenance - usually the major cost of a software system. Not part of "development", but definitely part of the software life cycle

The Java Language

• Java is a programming language that evolved from C++
  • Both are object-oriented
  • They both have much of the same syntax
• Began in the early 90's, originally used for programming in intelligent consumer-electronic devices (internal chips, etc).
• Was originally named Oak by its creator, but changed when it was reliazed that there was already a language called Oak
• When the Web took off in the early 90s, Java gained popularity for use in adding dynamic content to web pages
  • While applets surely helped Java gain quick popularity, they are by no means the most important use of the language
• Java is now used for a wide variety of purposes, and its large and rich set of pre-built packages makes it a very popular choice of software developers
• The Java language specification is owned and controlled by Sun Microsystems
  • API (Application Programmer Interface) documentation for standard libraries available on the Sun web site
  • Standard Development Kit, along with other development tools can be downloaded from java.sun.com
• Latest version is Java SE 6 -- Java Standard Edition 6.0

Compiling and Running a Java program

• Java code compiled to an intermediate level -- bytecode
• bytecode runs on an interpreter -- the Java Virtual Machine
• Each platform needs its own JVM, but the same bytecode (generally speaking) runs on any JVM on any platform (i.e. the compiled version is portable)
• Typically Slower runtime than languages like C++, since running on an interpreter (and due to other factors)

Basic Creation and Execution of a Java program

1. Create source code with a text editor, store to disk
   • Source code is just a plain text file. In Java, we give the filename an extension of .java to identify it as a source code file
2. Compilation -- The compiler does syntax checking, translation to bytecode in files with the .class extension
   • bytecode is a translation of the source code to an intermediate level of code
3. Execution of Java program
   • The loader is part of the Java Virtual Machine
   • It loads the bytecode into memory and executes the instructions via an interpreter for the given platform (Windows, Mac, Linux, etc)

Integrated Development Environments

• An Integrated Development Environment (IDE) is a software package that includes all necessary tools for creating a program. Typcially includes:
  • Text editor
  • Compiler
  • Loader
  • Debugger
  • ability to launch and run applications from within IDE environment
  • Other useful tools
• Java IDEs frequently use the Java Standard Development Kit (SDK) tools underneath, and provide a graphical interface through menus to access the underlying tools.
• Examples of Java IDEs
  • NetBeans
  • Eclipse

Some Important Java Tools

• javac - java compiler
• java - java interpreter
• jar - the java archive utility
• javadoc - utility for auto-generating Java documentation API pages
• JSP - Java Server Pages
• JRE - Java Runtime Environment
• J2SDK - Java 2 Standard Development Kit (sometimes JDK, Java Development Kit, for short) -- includes JRE

Comparisons

Some benefits of Java (over C++) -- IMHO

• Vast collection of packages available in the Standard Development Kit (SDK)
  • Easy-to-use API descriptions in HTML format on the Sun web site
  • Standard format for building API descriptions for classes
• Easier to build programs with graphic interfaces (GUI)
  • latest packages for GUI (Swing classes) not platform specific
  • compiled bytecode runs on multiple platforms
  • In C++, one would commonly have to use the GUI libraries for each different platform
• Some syntax has been made simplified
• Java Runtime Environment (JRE) does some things for you
  • Automatic garbage collection (for dynamically allocated objects)
  • more dynamic run-time checking
  • automatic dynamic binding and polymorphic behavior

Some benefits of C++ (over Java) -- IMHO

• Programmer has more control and power in C++
  • In C++, programmer responsible for the details
  • Control over addresses with pointers
  • More control over efficient execution time and resource allocation/deallocation
• C++ programs will typically run faster, because
  • compiled to machine's native instruction set
  • dynamic allocation doesn't have to be used for all objects
  • programmer has more power to optimize what they want
• C++ still has some extra and versatile features (that Java doesn't), like operator overloading and multiple inheritance

Programming is about Problem Solving

• Algorithm - a finite sequence of steps to perform a specific task
  • To solve a problem, you have to come up with the necessary step-by-step process before you can code it
  • This is often the trickiest part of programming
• Some useful tools and techniques for formulating an algorithm
  • Top-down Refinement: Decomposing a task into smaller and simpler steps, then breaking down each step into smaller steps, etc
  • Pseudocode: Writing algorithms informally in a mixture of natural language and general types of code statements
  • Flowcharting: If you can visualize it, it's often easier to follow and understand!
• Testing - algorithms must also be tested!
  • Does it do what is required?
  • Does it handle all possible situations?
• Syntax vs. Semantics
  • Syntax -- the grammar of a language.
    A syntax error: "I is a programmer."
  • Semantics -- the meaning of language constructs
    Correct syntax, but a semantic error: "The car ate the lemur."

A sample Java program

import java.util.Scanner;                 // brings in a library

class Sample                              // class that contains this program
{

  public static void main(String[] args)  // main function, start of program
  {
    Scanner input = new Scanner(System.in);  // creation of object to
                                             // read keyboard input

    int year = 2014;                      // an integer variable declaration
    String entry;                         // a String variable

    System.out.println("Welcome to Java Programming " + year);
    System.out.print("Type 'Q' to quit: ");
    entry = input.next();                 // read input from user

    System.out.print("Goodbye!\n");
  }                                       // end of main()

}                                         // end of class block