L EC. 01: J AVA FUNDAMENTALS Fall Java Programming

C ONTENTS  Brief history of Java  Features of Java  JDK, JRE, JVM and bytecode  Developing and executing Java programs  Basic syntax and semantics of Java Fall Java Programming

J AVA TECHNOLOGY  Java technology is a software-only platform running on top of other hardware-based platforms.  Including  Java programming language A general-purpose, concurrent, strongly typed, class-based object- oriented language  Tools Compiler, debugger, documentation tool, launcher, web service, …  Application Programming Interfaces (APIs) Large amount ready-made software components to make programming easier  Deployment methodology Java Web Start, Java plug-in  Integration libraries JDBC, JNDI, Java RMI  Java Virtual Machine (JVM) Fall Java Programming

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P AST OF J AVA  Conceived by a design team of Sun Microsystems in 1991  Original language goal  A platform-independent language that could be used to create software to be embedded in various consumer electronic devices  Switching to Internet programming with the emergence of the World Wild Web  The syntax and object model of Java inherits from C and C++ respectively. Fall Java Programming

F EATURES OF J AVA INCLUDING …  Highly portable  Highly dynamic  Suitable for distributed architectures  Highly secure  Object-oriented  Robust  Hybrid of compiling and interpreting  Multithreaded Fall Java Programming The secret to make Java platform- independent and secure is the JVM (Java Virtual Machine) and Java bytecode.

T YPES OF J AVA PROGRAMS  Based on the usages and runtime environments, Java programs are classified as:  Stand-alone programs  Java applets  Java servelets  JavaBeans  The syntactic and semantic rules are the same for these four types of Java programs.  The differences among them are the APIs required to develop and execute programs. Fall Java Programming

S TAND - ALONE J AVA PROGRAMS  A stand-alone Java program (also called Java application) can be only executed on the computer where the program is stored.  Two types of stand-alone programs  Console mode  Window mode Fall Java Programming

J AVA APPLETS  An applet is a special kind of Java program that is designed to be transmitted over the Internet and automatically executed by a Java-compatible web browser.  An applet is downloaded automatically when users click hyperlink containing applets, without further interaction with the user.  Applets are small programs which are typically used to display data provided by the server, handle user input, or provide simple functions, such as a loan calculator, that execute locally, rather than on the server.  Applets greatly reduce the load of servers. Fall Java Programming

J AVA SERVELETS  A java servlet runs within a Web server which receives and responds to requests from Web clients, where the requests are transmitted via HTTP (Hyper Text Transport Protocol). Fall Java Programming

J AVABEANS  A bean is a Java class with method names that follow the JavaBeans API specifications.  Since all the beans follow the same specifications, they are easily to be integrated with other programs.  For example, all the Java classes supported by IDE (Integrated Development Environment), such as Eclipse and NetBeans, are Java beans.  A bean is used as a help class, instead of a driven class.  A help class is used to provide specific functions such as JButton, JFrame.  A driven class is used to control the process of a task. Fall Java Programming

JDK  Java Development Kit (JDK) is a collection of software which constructs an environment for developing Java programs.  JDK editions  Java Standard Edition (J2SE) J2SE can be used to develop client-side standalone applications or applets.  Java Enterprise Edition (J2EE) J2EE can be used to develop server-side applications such as Java servlets and Java ServerPages.  Java Micro Edition (J2ME) J2ME can be used to develop applications for mobile devices such as cell phones. Fall Java Programming

JRE  The JRE (Java Runtime Environment) is a collection of software which creates an environment for running Java program.  The JRE consists of the Java Virtual Machine (JVM), Java platform core classes, and supporting Java platform libraries. Fall Java Programming

J AVA BYTECODE AND JVM  Java bytecode is a intermediate language, instead of the executable code of any specific platform, generated from Java compiler.  Currently, some other languages, such as Python and Ada, can be translated into Java bytecode.  JVM is a virtual machine (i.e. a software implemented abstraction of a specific underlying platform) which supports the running environment for interpreting Java bytecodes.  JVMs may be developed by any company as long as it adhere to the JVM specification published by Oracle Corporation and to related contractual obligations.  To execute Java bytecodes, they are either interpreted by JVM or translated to native language, by using JIT (Just-In-Time) compiler, for execution. Fall Java Programming

Fall Java Programming 14 The output of the compiler is.class file