Download Java - ELTE

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
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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
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Integrated Development Environment
Development
Debug
UML
Exchange
ADF
Database
Synchronized changes
XML
SCM
1-22
HTML
Deployment
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Exploring the JDeveloper Environment
Component Palette
System Navigator
1-23
Code Editor
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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.