Chapter 1 Introduction to Java and JBuilder

Introduction to Java Programming Y. Daniel Liang Introduction  What is a computer? – Electronic devices that stores and process data – Includes both hardware and software  Hardware – physical aspects that you can see – – – – Central Processing Unit (CPU) Memory (main memory) Storage Devices (hard disk, floppy disk, CDs, tapes) Input and Output Devices (monitors, keyboards, mice, printers) – Communication Devices (modems and network interface cards) Hardware  Central Processing Unit (CPU) – Brain of a computer – Retrieves instructions from memory and executes them – 2 components:  control unit – controls and coordinates the actions of the other components  arithmetic/logic unit – perform numeric operations (addition, subtraction, multiplication, division) – Perform logic operations (comparison)  Built on semiconductor chip with millions of transistors Hardware  Memory (main memory) – Data are encoded as a series of bits. – Bit – binary digit: zero and one – Stores data and program instructions for CPU to execute – A memory unit is an ordered sequence of bytes, each holding 8 bits – Encoding scheme: ASCII Hardware  Memory (main memory) – A program and its data must be brought to memory before they can be executed – The content of memory is lost when new infor is placed in it. – Each byte has a unique address, used to locate the byte. – Can be accessed in any order, thus is called RAM (Random-access memory) – 1 Megabyte (MB) is about 1 million bytes. – Also built on silicon semiconductor ships containing thousands of transistors, but less complicated. – Memory is volatile, the content is lost when the power is turned off. Hardware  Storage Devices (hard disk, floppy disk, CDs, tapes) – Programs and data are stored permanently on storage devices and moved to memory when computer actually uses them. – 4 main types of storage devices: Disk drives (hard disks, floppy disks)  CD drives (CD-R, CD-RW, DVD). DVD stands for Digital versatile disc.  Tape drives  USB flash drives  Hardware  Input and Output Devices (monitors, keyboards, mice, printers) – Allows user to communicate with the computer – Common input devices: keyboards, mice – Common output devices: monitors, printers. Hardware  Communication Devices (modems and network interface cards) – To create network of computers Software  Software/computer program – invisible instructions that control the hardware and make it perform specific tasks. – Tell computer what to do in computer/machine language Software  Computer languages 1. Machine language 2. Assembly language 3. High level language Software  Machine language – a set of primitive instructions built into every computer – Different for different types of computers. – The instructions are in the form of binary code, e.g. to add 2 numbers (very tedious):  1101101010011010 Software  Assembly language – Low-level programming language which uses mnemonic to represent machine-language instructions – E.g.: ADDF3 R1, R2, R3 – Assembly code need to be converted into machine code by using an assembler – Assembly program platform dependent  Combination of mnemonic and machine instruction  is Software  High-level language – English-like and easy to learn and program. – E.g.:  Area = 5 * 5 * 3.1415; – COBOL, FORTRAN, BASIC, Pascal, Ada, C, Visual Basic, Delphi, C++, C#, Java – Source program is compiled into machine code by a compiler and linked to supporting library code by a linker to form an executable file. Fig. 1.4 Software  High-level language (continue) – Can port/move a source program to any machine with appropriate compilers but the source program must be recompiled – Java program, compiled it once into intermediate machine code known as bytecode. Bring the bytecode to any computer with a JVM (Java Virtual Machine). JVM interprets the bytecode into the machine codes and execute them. An overview of the java development process. Source: http://java.sun.com/docs/books/tutorial/getStarted/intro/definition.html Through the Java VM, the same application is capable of running on multiple platforms. Source: http://java.sun.com/docs/books/tutorial/getStarted/intro/definition.html Software  Compiling versus interpreting – Compiling translates the high-level code into a target language code as a single unit – Interpreting translates the individual steps in the high level code one at a time. Each step is execute immediately after it is translated. Software  Operating system (OS) – – – – Software that controls and manages the systems Fig. 1.6, page 36. E.g.: Windows (98, NT, XP, ME), MacOS, Linux etc. Major tasks Controlling and monitoring system activities (security, input, output, file directories, make sure programs running together do not interfere with each other)  Allocating and assigning system resources to program  Scheduling operations  – Multiprogramming – multiple programs to run simultaneously by sharing CPU – Multithreading – allows concurrency within a program; it subunits can run at the same time (e.g. editing and saving at the same time) – Multiprocessing/parallel processing – use 2 or more processors together to perform a task. What Is Java?  History  Characteristics of Java History     James Gosling Oak – 1991, for embedded consumer electronic appliances Renamed Java, 1995, for developing Internet applications HotJava – The first Java-enabled Web browser  Java applets – java programs that run from a Web browser – http://javaboutique.internet.com/movingtree/ Characteristics of Java            Java is simple Java is object-oriented Java is distributed Java is interpreted Java is robust Java is secure Java is architecture-neutral Java is portable Java’s performance Java is multithreaded Java is dynamic Java IDE Tools  Inprise JBuilder Visual J++ Café  Microsoft  Symantec  Forte by Sun MicroSystems  IBM Visual Age for Java 6.0 (free, open-source IDE, runs on  NetBeans  JCreator Windows, Linux, Solaris, and the MacOS) LE 4.0 (free) by Xinox Software Java Language Specification, API, JDK and IDE  Java Language Specification – Technical definition of the language which includes the syntax and semantics of the Java Programming language (java.sun.com/docs/books/jls)  API – Contains predefined classes and interfaces for developing Java programs. – 3 editions of Java API J2SE - version Java SE 6.0 (jdk1.6.0_02)  J2EE  J2ME  Java Language Specification, API, JDK and IDE  JDK – A set of programs for developing and testing Java program, each of which is invoked from a command line.  IDE (integrated development environment) – Software that provides integrated development environment (editing, compiling, building, debugging and online help) for rapidly developing Java program Getting Started with Java Programming A Simple Java Application Programs  Compiling  Executing Applications A Simple Application Example 1.1 //This application program prints Welcome //to Java! public class Welcome { public static void main(String[] args) { System.out.println("Welcome to Java!"); } } Source Run Creating, compiling and executing a Java Programs  Fig. 1.11, page: 44. Compiling Programs  On command line – javac file.java Java Source File Compiler Bytecode Executing Applications  On command line – java classname Bytecode Java Interpreter on Windows Java Interpreter on Linux ... Java Interpreter on Sun Solaris Example javac Welcome.java java Welcome output:... Anatomy of a Java program  Comments  Reserved  Modifier  Statement words  Block  Class  Method  The main method Anatomy of a Java program  Comments – – – – Documents the program for understanding purpose Ignored by compiler // /* */  Reserved words or keywords – Words that have specific meaning to the compiler and cannot be used for other purposes in the program – E.g: public, static, class, void Anatomy of a Java program  Modifier – Certain reserved words are modifiers that specify the properties of the data, methods and class and how they can be used. – E.g: public, private, static, final, abstract, protected.  Statement – Represents an action or a sequence of actions – Ends with semicolon (;)  Block – Groups the components of the program – Begins with opening brace { and ends with a closing brace } – Class block, method block Anatomy of a Java program  Class – Program is defined by using one or more class – Will be covered in more details later.  Method – A collection of statements that perform a sequence of operations. – Can be used without fully understanding how it works. – Invoke by calling the method name with the requirement argument  The main method – A special method where the program execution begins. – JVM invokes the main method to execute an application. Summary