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Introducing the Javaand Oracle Platforms

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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

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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

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Key Benefits of Java

• Object-oriented

• Interpreted and platform-independent

• Dynamic and distributed

• Multithreaded

• Robust and secure

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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 Implementation Integrationand testingDesign

CLASS MODELS

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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

Movie.java

JVM

Running programMovie.class

(javac) (java)

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Using Java with EnterpriseInternet Computing

Web server

Application server

PresentationBusiness

logic

• Servlets• JavaServer Pages (JSPs)

• Enterprise JavaBeans (EJB)• CORBA

Client Data

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Using the Java Virtual Machine

Operating system

JVM

Application

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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.

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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

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Implementing Securityin the Java Environment

Interface-specific access

Class loader

Bytecode verifier

Language and compiler

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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

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Using Java with Oracle 10g

Oracledatabase

Web serverClient

Application server

PresentationBusiness

logic

Data

OracleApplication Server

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Java Software Development Kit

Sun Java J2SE (known as JDK and Java SDK) provides:

• Compiler (javac)

• Core class library– classes.zip– rt.jar

• Debugger (jdb)

• Bytecode interpreter: The JVM (java)

• Documentation generator (javadoc)

• Java Archive utility (jar)

• Others

J2SE

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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

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Integrated Development Environment

Development

UML

ADF

XML

SCM

Debug

Exchange

Database

HTML

Deployment

Synchronized changes

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Exploring the JDeveloper Environment

System Navigator Code Editor Property Inspector

Component Palette

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Oracle 10g Products

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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.