Agenda

• Understand the activity of programming
• Learn about the architectures of computers
• Learn about abstractions of programming languages
• Become familiar with meaning of Java
• Understand differences between Java compilation and interpretation
• The "Hello World" example in Java
• How Will Java Change My Life?

Prerequisites

• Computer savvy (file management, text editing)
• Problem solving skills
• Time management
• High school math (algebra, trigonometry)
• No prior programming background required

What is a computer?

• Conventionally:
  • Central processing unit
  • Memory
  • Peripherals
  • Executes very simple instructions
  • Executes instructions very rapidly
  • General purpose device
  • Programs describe specific actions

Schematic Diagram of a Computer

What is a computer?

The computer is the network
(8 Fallacies of Distributed Computing)

1. The network is reliable
2. Latency is zero
3. Bandwidth is infinite
4. The network is secure
5. Topology doesn't change
6. There is one administrator
7. Transport cost is zero
8. The network is homogeneous

What Is Programming?

• Computers are programmed to perform tasks
• Different tasks = different programs
• Program
  • Sequence of basic operations executed in succession
  • Contains instruction sequences for all tasks it can execute
• Sophisticated programs require teams of highly skilled programmers and other professionals

Programming Languages

• Machine/Virtual Machine
  21 40 16 100 163 240
• Assembler
  iload intRate
  bipush 100
  if_icmpgt intError
• High-level language
  if (intRate > 100) . . .

Computers are mind magnification tools

• The tools are beginning to look less like machines and more like part of our minds
• Like other forms of expression such as writing, painting, sculpture, animation, and filmmaking
• OOP is part of this movement toward using computers as an expressive medium

The Progress of Abstraction

All programming languages provide abstractions.

• Assembly language is a small abstraction of the underlying machine.
• "Imperative" languages are abstractions of assembly languages.
• Problem solving: mapping from "problem space" to "solution space"
• A solution space is a machine - it is very constrained
  • programs are difficult to write
  • programs are expensive to maintain
• Alternative to modeling the machine is to model the problem you are trying to solve.
• C, PASCAL - all problems are procedures
• LISP - all problems are ultimately lists
• PROLOG - all problems are logical decisions (formulas)
• Smalltalk - represent solution elements in your problem as experts - social metaphor
• The elements in the problem space and their representations in the solution space are objects.
• SORCER: represent solution elements as distributed services (service providers) as network objects

SORCER Vision

Object Abstraction

• OOP: a higher level of abstraction
• Bjarne Stroustrup: Higher level of abstraction allows details to be hidden, which allows code to be shorter. The more details, the more mistakes. Plus, the more code you have, the harder it is to maintain. And, code at higher levels of abstraction is amenable to tools that analyze and optimize.
• Can think in terms of problem, not solution
• Vocabulary facilitates communication: A bank has Accounts, Customers, Balances, etc...

What is Java?

• 
• Island of Indonesia
• Object-Oriented Philosophy
• Programming language
• API
• Platform
• Freedom
• Security
• Internet networking

Object-Oriented Philosophy

• Everything is object (active data in your problem space)
• A program is a bunch of objects telling each other what to do by sending messages
• Each object has its own memory made up of other objects
• Every object has a type (has its origin - class)
• All objects of a particular type can receive the same messages

• What Is an Object?

  An object is a software bundle of variables and related methods. Software objects are often used to model real-world objects you find in everyday life.

• What Are Messages?

  Software objects interact and communicate with each other using messages.

• What Are Classes?

  A class is a blueprint or prototype that defines the variables and the methods common to all objects of a certain kind.

Java Programming Language

• Is very object-oriented
• Enforces type safety at run-time (safe)
• Platform-independent (highly portable - "write once, run anywhere")
• Designed for the Internet
• Supports exceptions
• Supports multi-threading
• Rich library (API)
• Uses garbage collection
• Is dynamically linked
• Is dynamically extensible
• 5 data types (primitives, array, class, interface, null)
• Includes eight primitive types
• Low-coupling; high-cohesion APIs

Exceptions

• Error handling that's "structured"
• Like a "goto" from error to handler
• Built into the Java language
• Java compiler forces client programmers to deal with potential errors

Multi-threading

• Multi-threading built into Java
• Like multiple processes in same address space
• Synchronization built into Java
• Helps you do several things at once:
  responsive UIs, animations, server apps, ...
• Designed to work cross-platform

Java APIs

• Sun's goal: abstract OS interface
• I/O: datat to/from files, strings, sockets, ...
• GUI: AWT, 1.1 event model, Swing
• Software Components: JavaBeans
• Net programming: Applets, java.net, RMI
• Accessing SQL databases: JDBC

Compiling and Running

Compiler machine dependent environment

The JVM model

 
Java is also unusual in that each Java program is both compiled and interpreted. With a compiler, you translate a Java program into an intermediate language called Java bytecodes--the platform-independent codes interpreted by the Java interpreter. With an interpreter, each Java bytecode instruction is parsed and run on the computer. Compilation happens just once; interpretation occurs each time the program is executed.

Linking, Optimization, and Execution

Java Virtual Machines

You can think of Java bytecodes as the machine code instructions for the Java Virtual Machine (Java VM). Every Java interpreter, whether it's a Java development tool or a Web browser that can run Java applets, is an implementation of the Java VM. The Java VM can also be implemented in hardware.

Java bytecodes help make "write once, run anywhere" possible. You can compile your Java program into bytecodes on any platform that has a Java compiler. The bytecodes can then be run on any implementation of the Java VM. For example, the same Java program can run on Windows NT, Solaris, and Macintosh.

Java virtual machines (JVMs), Java development kits (JDKs), Java runtime environments (JREs)

• Compilers for the Java programming language
  • bytecode compilers — tools that translate Java source code (.java files) to bytecode (.class files)
  • native compiler — tools that translate either source code or bytecode to native executables (e.g. .exe files under Windows)
• Java virtual machines (JVM), development kits (JDK) and runtime environments (JRE)
  • JDKs and JREs - complete packages to either develop (JDK) or run (JRE) Java applications, applets etc.
  • standalone JVMs - mostly research projects that rely on an external class library implementations
  • embedded systems - environments that run on systems with limited memory and CPU resources, sometimes integrated into the operating system
  • just-in-time (JIT) compilers - mostly integrated in the JVM, they convert bytecode on demand to faster machine code
  • HotSpot JVM - It features techniques such as just-in-time compilation and adaptive optimization designed to improve performance
• Java class file optimization and compression - tools and techniques to reduce the size of Java class files

Just-in-time (JIT) compilers

Just-in-time (JIT) compilers are essentially fast traditional compilers that translate the Java technology bytecodes into native machine code on the fly. A JIT running on the end user's machine actually executes the bytecodes and compiles each method the first time it is executed.

The Java HotSpot VM Architecture

Rather than compiling method by method, just in time, the Java HotSpot VM immediately runs the program using an interpreter, and analyzes the code as it runs to detect the critical hot spots in the program. Then it focuses the attention of a global native-code optimizer on the hot spots.

The Java HotSpot Client VM, on the left, and the Java HotSpot Server VM, on the right, use a different compiler but otherwise interface to the same virtual machine, using the same garbage collection (GC) routine, interpreter, thread and lock subsystems, and so on.

The J2SE SDK contains both of the these systems in the distribution, so developers can choose which system they want by specifying -client or -server

Java Related Compilation Summary

Benchmarking programming languages?
"There are lies, damn lies and Benchmarks".

How can we benchmark a programming language?
We can't - we benchmark programming language implementations.

How can we benchmark language implementations?
We can't - we measure particular programs.

The Computer Language Shootout Benchmarks

The Java is Faster than C++ and C++ Sucks Unbiased Benchmark

Performance Comparison of Java/.NET Runtimes
Linpack Benchmark FAQ

Self Check

1. Does a person who uses a computer for office work ever run a compiler?
4. Where is a program stored when it is not currently running?

Answers

1. No–a compiler is intended for programmers, to translate high-level programming instructions into VM (byte) code.
   Yes–a JVM compiler can compile opcodes into a physical machine code.
2. In secondary storage, typically a hard disk on a local host or a remote host . Class loaders are used when a program is located on of remote hosts.

The Java Platform

The Java platform has two components:

• The Java Application Programming Interface (Java API)
• The Java OS (implemented by JVM)
• The Java Runtime Environment (implements Java VM)

• "Write Once, Run Anywhere" -> Java Platform
• All kinds of systems can talk to each other -- from smart cards to supercomputers -- regardless of the underlying hardware or system software.
• When software written in the Java programming language is compiled with Java technology, byte code results. The Java virtual machine, can explain (interpret) that byte code to any platform on which the Java virtual machine is installed. This means no more porting of programs to platforms.

Java Card Technology

End-to-End Computing

Java™ Technology Leads the Way…

New application development by language ( Soundview TG, 2001)
 

Freedom

• Hardware (CPU)
• Operating system
• Object mobility
• Network protocols
• Internationalization

Security

• Two Levels of Security
  • Low-level intrinsic security
  • Resource level security
• Sandbox Security Model
  • Class loaders
  • Verification
  • Security Manager
• Language (including, type safety)
• Beyond the Sandbox - protection domains
• JAAS, JSSE, GSS, JCE, JCA, JERI, Jini Security

Internet Networking

• URLs, TCP, UDP, multicast networking
• Applets/Plug-ins/Servlets/JSP/JSF
• RMI, JERI, RMI Activation
• EJBs
• Java IDL, RMI/IIOP
• Jini Network Technology
• JXTA P2P Computing
• Web Services (JAX...)
• Java Database Connectivity (JDBC)

Three Laws of Computing

• Moore's Law
  • Computing power doubles every 18 months
• Gilder's Law
  • Network bandwidth capacity doubles every 12 months
• Metcalfe's Law (Net Effect)
  • Value of network increases exponentially as number of participants increases

Waves of Computing

Many Kinds of Networks and Technologies

Applets on a Web Page

Jmol is a free, open source molecule viewer written in Java. It is a collaboratively developed visualization and measurement tool for chemical scientists.

Features

• Available as both a Java application and as a web browser applet
• Reads many types of files: ABINIT, ACES II, ADF (Amsterdam Density Functional), CML (Chemical Markup Language), Dalton, GAMESS, Gaussian 90/92/94/96/98, Ghemical, Jaguar, MDL molfiles, MOPAC 7/97/2002, PDB, XYZ (XMol).
• Animates the results of simulations.
• Displays measurements inter-atomic distances, bond angles, and dihedral angles from atomic coordinates as a simulation progresses.
• Animates the computed vibrational modes from any of the quantum chemistry packages mentioned above.
• Supports RasMol/Chime scripting
• Displays vectors (velocity, dipole, etc.), charges, atomic symbols, or atomic indexes during animation.
• Prints or exports images in these formats: GIF, JPG, PPM, BMP, PNG, PDF, PostScript, and PovRay (including animations).
• Can display unit cell boxes, and energy bands.

 

File Hello.java

1	public class Hello
2	{
3	public static void main(String[] args)
4	{
5	// display a greeting in the console window
6	System.out.println("Hello, World!");
7	}
8	}

 

A simple program

• public class ClassName
• public static void main(String[] args)
• // comment
   
• Method call
  object.methodName(parameters)
• System class
• System.out object
• println method

 

Syntax: Method Call

object.methodName(parameters) Example:   System.out.println("Hello, Dave!"); Purpose: To invoke a method of an object and supply any additional parameters

Compiling and Running

• Type program into text editor
• Save
• Open command shell
• Compile into byte codes
  javac Hello.java
• Execute byte codes
  java Hello

From Source Code to Running Program

 

Errors

• Syntax errors
  System.ouch.print("...");
  System.out.print("Hello);
• Detected by the compiler
• Logic errors
  System.out.print("Hell");
• Detected (hopefully) through testing

The Edit-Compile-Test Loop

How Will Java Change My Life?

I can't promise you fame, fortune, or even a job if you learn Java. Still, Java is likely to make your programs better and requires less effort than other languages. I believe that Java will help you do the following:

• Get started quickly: Although Java is a powerful object-oriented language, it's easy to learn, especially for programmers already familiar with C or C++.
• Write less code: Comparisons of program metrics (class counts, method counts, and so on) suggest that a program written in Java can be four times smaller than the same program in C++.
• Write better code: The Java language encourages good coding practices, and its garbage collection helps you avoid memory leaks. Java's object orientation, its JavaBeans component architecture, and its wide-ranging, easily extendible API let you reuse other people's tested code and introduce fewer bugs.
• Develop programs faster: Your development time may be as much as twice as fast versus writing the same program in C++. Why? You write fewer lines of code with Java and Java is a simpler programming language than C++.
• Avoid platform dependencies with 100% Pure Java: You can keep your program portable by avoiding the use of libraries written in other languages.
• Write once, run anywhere: Because 100% Pure Java programs are compiled into machine-independent bytecodes, they run consistently on any Java platform.
• Distribute software more easily: You can upgrade applets easily from a central server. Applets take advantage of the Java feature of allowing new classes to be loaded "on the fly," without recompiling the entire program.
• Learn selectively APIs: Focus on learning those parts of the library that you need for your programming projects.