Java™ How to Program, Sixth Edition - Part1

Today i started reading Java™ How to Program, Sixth Edition By H. M. Deitel - Deitel & Associates, Inc., P. J. Deitel - Deitel & Associates, Inc.

Nice book written By H. M. Deitel - Deitel & Associates, Inc., P. J. Deitel - Deitel & Associates, Inc.

I wanted to share few quotations found the book from the 1st chapter.

1) A computer is a device capable of performing computations and making logical decisions at speeds millions (even billions) of times faster than human beings can. For example, many of today's personal computers can perform a billion additions per second. A person operating a desk calculator could spend an entire lifetime performing calculations and still not complete as many calculations as a powerful personal computer can perform in one second.Today's fastest supercomputers can perform hundreds of billions of additions per second. And trillion-instructions-per-second computers are already functioning in research laboratories.

2) Computers process data under the control of sets of instructions called computer programs. These programs guide the computer through orderly sets of actions specified by people called computer programmers.

3) A computer consists of various devices referred to as hardware (e.g., the keyboard, screen, mouse, disks, memory, DVD, CD-ROM and processing units). The programs that run on a computer are referred to as software. Hardware costs have been declining dramatically in recent years, to the point that personal computers have become a commodity. Unfortunately, in the absence of significantly improved technology for software development, costs have been rising steadily as programmers develop ever more powerful and complex applications.

4) Input unit. This is the "receiving" section of the computer. It obtains information (data and computer programs) from input devices and places this information at the disposal of the other units so that it can be processed. Most information is entered into computers through keyboards and mouse devices. Information also can be entered in many other ways, including by speaking to your computer, by scanning images and by having your computer receive information from a network, such as the Internet.

5) Output unit. This is the "shipping" section of the computer. It takes information that the computer has processed and places it on various output devices to make the information available for use outside the computer. Most information output from computers today is displayed on screens, printed on paper or used to control other devices. Computers also can output their information to networks, such as the Internet.

6) Memory unit. This is the rapid-access, relatively low-capacity "warehouse" section of the computer. It retains information that has been entered through the input unit, so that it will be immediately available for processing when needed. The memory unit also retains processed information until it can be placed on output devices by the output unit. Information in the memory unit is typically lost when the computer's power is turned off. The memory unit is often called either memory or primary memory.

7) Arithmetic and logic unit (ALU). This is the "manufacturing" section of the computer. It is responsible for performing calculations, such as addition, subtraction, multiplication and division. It contains the decision mechanisms that allow the computer, for example, to compare two items from the memory unit to determine whether they are equal.

8) Central processing unit (CPU). This is the "administrative" section of the computer. It coordinates and supervises the operation of the other sections. The CPU tells the input unit when information should be read into the memory unit, tells the ALU when information from the memory unit should be used in calculations and tells the output unit when to send information from the memory unit to certain output devices. Many of today's computers have multiple CPUs and, hence, can perform many operations simultaneouslysuch computers are called multiprocessors.

9) Secondary storage unit. This is the long-term, high-capacity "warehousing" section of the computer. Programs or data not actively being used by the other units normally are placed on secondary storage devices (e.g., your hard drive) until they are again needed, possibly hours, days, months or even years later. Information in secondary storage takes much longer to access than information in primary memory, but the cost per unit of secondary storage is much less than that of primary memory. Examples of secondary storage devices include CDs and DVDs, which can hold up to hundreds of millions of characters and billions of characters, respectively.

10) As computers became more powerful, it became evident that single-user batch processing was inefficient, because so much time was spent waiting for slow input/output devices to complete their tasks. It was thought that many jobs or tasks could share the resources of the computer to achieve better utilization. This is called multiprogramming. Multiprogramming involves the simultaneous operation of many jobs that are competing to share the computer's resources. With early multiprogramming operating systems, users still submitted jobs on decks of punched cards and waited hours or days for results.

11) In the 1960s, several groups in industry and the universities pioneered timesharing operating systems. Timesharing is a special case of multiprogramming in which users access the computer through terminals, typically devices with keyboards and screens. Dozens or even hundreds of users share the computer at once. The computer actually does not run them all simultaneously. Rather, it runs a small portion of one user's job, then moves on to service the next user, perhaps providing service to each user several times per second. Thus, the users' programs appear to be running simultaneously. An advantage of timesharing is that user requests receive almost immediate responses.

12) These computers were "standalone" unitspeople transported disks back and forth between them to share information (often called "sneakernet"). Although early personal computers were not powerful enough to timeshare several users, these machines could be linked together in computer networks, sometimes over telephone lines and sometimes in local area networks (LANs) within an organization. This led to the phenomenon of distributed computing, in which an organization's computing, instead of being performed only at some central computer installation, is distributed over networks to the sites where the organization's work is performed. Personal computers were powerful enough to handle the computing requirements of individual users as well as the basic communications tasks of passing information between computers electronically.

13) Today's personal computers are as powerful as the million-dollar machines of just two decades ago. The most powerful desktop machinescalled workstationsprovide individual users with enormous capabilities. Information is shared easily across computer networks where computers called file servers offer a common data store that may be used by client computers distributed throughout the network, hence the term client/server computing. Java has become widely used for writing software for computer networking and for distributed client/server applications. Today's popular operating systems, such as UNIX, Linux, Apple Mac OS X (pronounced "O-S ten") and Microsoft Windows, provide the kinds of capabilities discussed in this section.

14) With the introduction of the World Wide Webwhich allows computer users to locate and view multimedia-based documents on almost any subject over the Internetthe Internet has exploded into one of the world's premier communication mechanisms.

15) Programmers write instructions in various programming languages, some directly understandable by computers and others requiring intermediate translation steps. Hundreds of computer languages are in use today. These may be divided into three general types:

Machine languages

Assembly languages

High-level languages

16) Any computer can directly understand only its own machine language. Machine language is the "natural language" of a computer and as such is defined by its hardware design. Machine languages generally consist of strings of numbers (ultimately reduced to 1s and 0s) that instruct computers to perform their most elementary operations one at a time. Machine languages are machine dependent (i.e., a particular machine language can be used on only one type of computer).

17) Machine-language programming was simply too slow and tedious for most programmers. Instead of using the strings of numbers that computers could directly understand, programmers began using English-like abbreviations to represent elementary operations. These abbreviations formed the basis of assembly languages. Translator programs called assemblers were developed to convert early assembly-language programs to machine language at computer speeds.

18) Computer usage increased rapidly with the advent of assembly languages, but programmers still had to use many instructions to accomplish even the simplest tasks. To speed the programming process, high-level languages were developed in which single statements could be written to accomplish substantial tasks. Translator programs called compilers convert high-level language programs into machine language. High-level languages allow programmers to write instructions that look almost like everyday English and contain commonly used mathematical notations.

19) The process of compiling a high-level language program into machine language can take a considerable amount of computer time. Interpreter programs were developed to execute high-level language programs directly, although much more slowly. Interpreters are popular in program-development environments in which new features are being added and errors corrected. Once a program is fully developed, a compiled version can be produced to run most efficiently.

20) The C language was evolved from B by Dennis Ritchie at Bell Laboratories and was originally implemented in 1972. It initially became widely known as the development language of the UNIX operating system. Today, most of the code for general-purpose operating systems (e.g., those found in laptops, desktops, workstations and small servers) is written in C or C++.

21) C++, an extension of C, was developed by Bjarne Stroustrup in the early 1980s at Bell Laboratories (now part of Lucent). C++ provides a number of features that "spruce up" the C language, but more important, it provides capabilities for object-oriented programming. C++ is a hybrid languageit is possible to program in either a C-like style, an object-oriented style or both.

22) The Green project ran into some difficulties. The marketplace for intelligent consumer-electronic devices was not developing in the early 1990s as quickly as Sun had anticipated. The project was in danger of being canceled. By sheer good fortune, the World Wide Web exploded in popularity in 1993, and Sun people saw the immediate potential of using Java to add dynamic content, such as interactivity and animations, to Web pages. This breathed new life into the project.

Sun formally announced Java at a major conference in May 1995. Java garnered the attention of the business community because of the phenomenal interest in the World Wide Web. Java is now used to develop large-scale enterprise applications, to enhance the functionality of Web servers (the computers that provide the content we see in our Web browsers), to provide applications for consumer devices (e.g., cell phones, pagers and personal digital assistants) and for many other purposes.

23) COBOL (COmmon Business Oriented Language) was developed in the late 1950s by computer manufacturers, the U.S. government and industrial computer users. COBOL is used for commercial applications that require precise and efficient manipulation of large amounts of data. Much business software is still programmed in COBOL.

24) The Ada programming language was developed under the sponsorship of the U.S. Department of Defense (DOD) during the 1970s and early 1980s. Hundreds of separate languages were being used to produce the DOD's massive command-and-control software systems. The DOD wanted a single language that would fill most of its needs. The Ada language was named after Lady Ada Lovelace, daughter of the poet Lord Byron. Lady Lovelace is credited with writing the world's first computer program in the early 1800s (for the Analytical Engine mechanical computing device designed by Charles Babbage). One important capability of Ada, called multitasking, allows programmers to specify that many activities are to occur in parallel. Java, through a technique called multithreading, also enables programmers to write programs with parallel activities.

25) The BASIC (Beginner's All-Purpose Symbolic Instruction Code) programming language was developed in the mid-1960s at Dartmouth College as a means of writing simple programs. BASIC's primary purpose was to familiarize novices with programming techniques.

26) The Java compiler translates the Java source code into bytecodes that represent the tasks to be performed during the execution phase (Phase 5). Bytecodes are executed by the Java Virtual Machine (JVM)a part of the JDK and the foundation of the Java platform. A virtual machine(VM) is a software application that simulates a computer, but hides the underlying operating system and hardware from the programs that interact with the VM. If the same VM is implemented on many computer platforms, applications that it executes can be used on all those platforms. The JVM is one of the most widely used virtual machines.

27) The program must be placed in memory before it can executea process known as loading. The class loader takes the .class files containing the program's bytecodes and transfers them to primary memory. The class loader also loads any of the .class files provided by Java that your program uses. The .class files can be loaded from a disk on your system or over a network (e.g., your local college or company network, or the Internet).

28) As the classes are loaded, the bytecode verifier examines their bytecodes to ensure that they are valid and do not violate Java's security restrictions. Java enforces strong security, to make sure that Java programs arriving over the network do not damage your files or your system (as computer viruses and worms might).

29) JVM executes the program's bytecodes, thus performing the actions specified by the program. In early Java versions, the JVM was simply an interpreter for Java bytecodes. This caused most Java programs to execute slowly because the JVM would interpret and execute one bytecode at a time. Today's JVMs typically execute bytecodes using a combination of interpretation and so-called just-in-time (JIT) compilation. In this process, The JVM analyzes the bytecodes as they are interpreted, searching for hot spotsparts of the bytecodes that execute frequently. For these parts, a just-in-time (JIT) compilerknown as the Java HotSpot compilertranslates the bytecodes into the underlying computer's machine language. When the JVM encounters these compiled parts again, the faster machine-language code executes. Thus Java programs actually go through two compilation phasesone in which source code is translated into bytecodes (for portability across JVMs on different computer platforms) and a second in which, during execution, the bytecodes are translated into machine language for the actual computer on which the program executes.

About the Authors

Dr. Harvey M. Deitel, Chairman and Chief Strategy Officer of Deitel & Associates, Inc., has 43 years experience in the computing field, including extensive industry and academic experience. Dr. Deitel earned B.S. and M.S. degrees from the Massachusetts Institute of Technology and a Ph.D. from Boston University. He worked on the pioneering virtual-memory operating-systems projects at IBM and MIT that developed techniques now widely implemented in systems such as UNIX, Linux and Windows XP. He has 20 years of college teaching experience, including earning tenure and serving as the Chairman of the Computer Science Department at Boston College before founding Deitel & Associates, Inc., with his son, Paul J. Deitel. He and Paul are the co-authors of several dozen books and multimedia packages and they are writing many more. With translations published in Japanese, German, Russian, Spanish, Traditional Chinese, Simplified Chinese, Korean, French, Polish, Italian, Portuguese, Greek, Urdu and Turkish, the Deitels' texts have earned international recognition. Dr. Deitel has delivered hundreds of professional seminars to major corporations, academic institutions, government organizations and the military.

Paul J. Deitel, CEO and Chief Technical Officer of Deitel & Associates, Inc., is a graduate of the MIT's Sloan School of Management, where he studied Information Technology. Through Deitel & Associates, Inc., he has delivered Java, C, C++, Internet and World Wide Web courses to industry clients, including IBM, Sun Microsystems, Dell, Lucent Technologies, Fidelity, NASA at the Kennedy Space Center, the National Severe Storm Laboratory, Compaq, White Sands Missile Range, Rogue Wave Software, Boeing, Stratus, Cambridge Technology Partners, Open Environment Corporation, One Wave, Hyperion Software, Adra Systems, Entergy, CableData Systems and many other organizations. Paul is one of the most experienced Java corporate trainers having taught about 100 professional Java training courses. He has also lectured on C++ and Java for the Boston Chapter of the Association for Computing Machinery. He and his father, Dr. Harvey M. Deitel, are the world's best-selling Computer Science textbook authors.