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Introducing the Java and Oracle Platforms Copyright © 2004, Oracle. All rights reserved. Objectives After completing this lesson, you should be able to do the following: • Identify the key elements of Java • Describe the Java Virtual Machine (JVM) • Examine how Java is used to build applications • Identify the key components of the J2SE Java Development Kit (known as JDK or SDK) • Describe Java deployment options 1-2 Copyright © 2004, Oracle. All rights reserved. What Is Java? Java: • Is a platform and an object-oriented language • Was originally designed by Sun Microsystems for consumer electronics • Contains a class library • Uses a virtual machine for program execution 1-3 Copyright © 2004, Oracle. All rights reserved. Key Benefits of Java • • • • • 1-4 Object-oriented Interpreted and platform-independent Dynamic and distributed Multithreaded Robust and secure Copyright © 2004, Oracle. All rights reserved. An Object-Oriented Approach • Objects and classes – An object is a run-time representation of a “thing.” – A class is a “static definition of things.” • Class models elaborate: – – – – • Existing classes and objects Behavior, purpose, and structure Relationships between classes Relationships between run-time objects Same models exist throughout the project. Analysis Design Implementation CLASS MODELS 1-6 Copyright © 2004, Oracle. All rights reserved. Integration and testing Platform Independence • • • • Java source code is stored as text in a .java file. The .java file is compiled into .class files. A .class file contains Java bytecodes (instructions). The bytecodes are interpreted at run time. – The Java .class file is the executable code. Compile (javac) Movie.java 1-7 JVM (java) Movie.class Running program Copyright © 2004, Oracle. All rights reserved. Using Java with Enterprise Internet Computing Client Web server Application server Presentation Business logic • Servlets • JavaServer Pages (JSPs) 1-8 • Enterprise JavaBeans (EJB) • CORBA Copyright © 2004, Oracle. All rights reserved. Data Using the Java Virtual Machine Operating system JVM Application 1-10 Copyright © 2004, Oracle. All rights reserved. How Does JVM Work? • The class loader loads all required classes. – JVM uses a CLASSPATH setting to locate class files. • • JVM Verifier checks for illegal bytecodes. JVM Verifier executes bytecodes. – JVM may invoke a Just-In-Time (JIT) compiler. • Memory Manager releases memory used by the dereferenced object back to the OS. – JVM handles Garbage collection. 1-12 Copyright © 2004, Oracle. All rights reserved. Benefits of Just-In-Time (JIT) Compilers JIT compilers: • Improve performance • Are useful if the same bytecodes are executed repeatedly • Translate bytecodes to native instruction • Optimize repetitive code, such as loops • Use Java HotSpot VM for better performance and reliability 1-14 Copyright © 2004, Oracle. All rights reserved. Implementing Security in the Java Environment Language and compiler Class loader Bytecode verifier Interface-specific access 1-16 Copyright © 2004, Oracle. All rights reserved. Deployment of Java Applications • Client-side deployment: – JVM runs stand-alone applications from the command line. – Classes load from a local disk, eliminating the need to load classes over a network. • Server-side deployment: – Serves multiple clients from a single source – Is compatible with a multitier model for Internet computing. 1-18 Copyright © 2004, Oracle. All rights reserved. Using Java with Oracle 10g Client Web server Application server Presentation Business logic Oracle Application Server 1-19 Copyright © 2004, Oracle. All rights reserved. Data Oracle database Java Software Development Kit Sun Java J2SE (known as JDK and Java SDK) provides: • Compiler (javac) • Core class library – classes.zip – rt.jar 1-20 • Debugger (jdb) • • • Bytecode interpreter: The JVM (java) Documentation generator (javadoc) Java Archive utility (jar) • Others Copyright © 2004, Oracle. All rights reserved. J2SE Using the Appropriate Development Kit Java2 comes in three sizes: • J2ME (Micro Edition): Version specifically targeted at the consumer space • J2SE (Standard Edition): Complete ground-up development environment for the Internet • J2EE (Enterprise Edition): Everything in the J2SE plus an application server and prototyping tools 1-21 Copyright © 2004, Oracle. All rights reserved. Integrated Development Environment Development Debug UML Exchange ADF Database Synchronized changes XML SCM 1-22 HTML Deployment Copyright © 2004, Oracle. All rights reserved. Exploring the JDeveloper Environment Component Palette System Navigator 1-23 Code Editor Copyright © 2004, Oracle. All rights reserved. Property Inspector Oracle10g Products 1-24 Copyright © 2004, Oracle. All rights reserved. Summary In this lesson, you should have learned the following: • Java code is compiled into platform-independent bytecodes. • Bytecodes are interpreted by JVM. • Java applications can be stand-alone or implemented across an Internet-computing model. 1-25 Copyright © 2004, Oracle. All rights reserved.