What is Java? What can Java do?

What is Java?

Java is both a programming language and a platform.

　　Java programming language

Java is a high-level programming language with the following characteristics:

Simple
Object oriented
can be distributed
Can explain
Strong
Security
Structure of
Light
Powerful features
Multithreading
Dynamic

Java can be either compiled or interpreted. With the compiler, you can translate a Java program into an intermediate code-called a bytecode-that can be interpreted by the Java interpreter
Explains the platform-independent code. Through the interpreter, each Java byte instruction is parsed and then run on the computer. Just compile once and the program runs to explain
Perform. Explains how it works:

You can think of Java bytecode as a machine code instruction running on a Java Virtual machine (Java VM). Each Java interpreter, whether it is a Java development tool or can be shipped
A Web browser for Java applets is an instance of a Java VM. JAVAVM can also be implemented by hardware.

Java bytecode makes it possible to write once and run everywhere. Java programs can be compiled into bytecode on any platform that has a Java compiler. This byte code can be
Run on any Java VM. For example, the same Java program can run on WindowsNT, Solaris, and Macintosh.

　　Java Platform

A platform is a hardware or software environment in which programs run. The Java platform differs from most other platforms in that it is a pure software platform that runs on other hardware-based platforms. Big
Most other platforms are a combination of hardware and operating systems.

　　The Java platform consists of two parts: Java Virtual machine (Java VM) Java application interface (Java API)

We have introduced Java VMS, which are the foundation of the Java platform and can be ported to a variety of hardware-based platforms.

The Java API is a collection of software components that provide a number of useful functions, such as the graphical user interface (GUI). The Java API is grouped into libraries (packages) of related components.

Describes a Java program that runs on the Java platform, such as an application (application) or a small application (applet). , JAVAAPI and VMS separate Java programs from hardware dependencies.

As a platform-independent environment, Java is a bit slower than native code. However, smart compilers, well-modulated interpreters and instant byte-code compilers can
Keep Java's performance close to the local code without sacrificing portability.

//==============================================

As a learning Java person, first of all we need to understand what Java is, what Java can do, and the historical background of Java, only when we understand the basics of Java, we learn Java to do less.

Java the historical background

Java is a generic term for the Java object-oriented programming language (hereinafter referred to as the Java language) and the Java platform introduced by Sun Microsystems Corporation. Co-developed by James Gosling and co-workers, and was formally launched in 1995. Originally known as Oak, Java was designed for embedded chips in consumer electronics in the 1991. Renamed Java in 1995 and redesigned to develop Internet applications. Java-enabled HotJava browser (Java applet support) shows the charm of Java: Cross-platform, dynamic web, Internet computing. Since then, Java has been widely accepted and promoted the rapid development of the web, commonly used browsers support Javaapplet. Java technology, on the other hand, is constantly being updated. Since the advent of Java is very popular, rapid development, the C + + language to form a strong impact. In the global cloud computing and mobile Internet industry environment, Java has a significant advantage and broad prospects. 2010 Oracle Company acquires Sun Microsystems.

Since Sun was acquired by Oracle, the future of Java has become confusing, and many programmers are confused. On April 9, 2010, James Goslin, the father of Java, announced his departure from Oracle on his personal blog, adding a layer of fog to the outlook for Java. But after entering the May, everything began to become clear.

On the active publishing site of Oracle, multiple campaigns on Java have been published continuously. May 12, Oracle main product Owner

Dave

Hofert will talk about the improvement and innovation of javase commercial application. According to the literature, in this presentation, Davehofert will address the following issues: platform support between business and Community editions

The difference between the holders. How to get expert help to help enterprises enhance their Java applications. Security patching issues for older versions. The publishing tools and updates that you can use. June 18, 19, 20, 27th, respectively

In Helsinki, Stuttgart, Budapest,

A meeting of Oracle, sun experts and users will be held in London to discuss Java's development path with users. The main issues discussed include how Oracle will continue to invest and improve

Java technology, and also informs users about the latest news from Javase, javame experts, JavaFX and JDK7, and Oracleberkeley

Information about the DB. May 3, the father of Java, who has left oracle for nearly one months, James Goslin on his blog about NetBeans 6.9 and

FX1.3 released care. The release of the latest version of these two projects proves that Oracle has begun to deliver on its original commitments. James Goslin in its early blog, also revealed that will not give up

Java business, just need to address some of the legal issues with Oracle. All these indications are that Oracle will never easily abandon Java's huge cake, and Oracle

Also began to learn more about the open source community

Respect. First in terms of the commercial version of the JDK, Oracle will continue to dig deeper into Java's business interests and integrate with its inherent offerings. With respect to the Community version, Oracle will

Java developers to explore and develop Java technologies. One of the products that needs to be specifically mentioned here is Oracle

BerkeleyDB, the product is an open-source, non-relational database product that Oracle has always supported, and if Oracle can integrate BerkeleyDB with Java in depth today, it will bring more vitality and life to Java. Judging from James Goslin's performance, he seems to have reached an understanding with Oracle, and Android, which is the first built-in Java-enabled operating system, is written in the Java language. The level of Android development is largely dependent on

Is the Java language Core competency solid. On the other hand, 3G applications are often combined with enterprise-class applications. Therefore, in the 3g-android course system, the Android course will be

The Java EE course is closely integrated with Android courses, supplemented by Java EE courses, with real enterprise-level projects, not only to gain a deep grasp of the Android platform-based smartphone development technology, but also to master the Intelligent Mobile Terminal and Java EE server retransmitting combines many areas of commercial application possibilities.

Java the role

Java programming is a huge, fast-growing field. Since the release of Java, as an object-oriented programming language, whether in the Internet programming, or in the teaching of programming, has shown significant advantages. Java 2 leveling is a mature software that has a significant impact on the development of supporting applications. In fact, Java itself is not complicated, just slightly more content. It is faster and better to use it for software development.

Another major feature of Java might be object oriented. Programming with an object-oriented approach is an implicit feature of all Java programs, and in the later part of this chapter we will see what it means. Java is not only object-oriented, but it also tries to avoid the difficulty and complexity of inheritance in other object-oriented languages, so you will find that Java is a very simple and easy-to-learn language.

In the present stage, the most promising development language is Java,java language is cross-platform, write Once,run anywhere is a phrase in Java, learn application programming, you can write programs on a computer, learn applets can be embedded in a small program on the Web page    , learn J2ME, can run the program on the mobile phone, everywhere has the shadow of Java ... Broadly divided into three versions j2me for embedded development such as mobile phone programs, J2SE Standard version of small and medium-sized software should be more for the C/s structure, but also the best start to learn Java; Simply speaking, you can do game software, chat tools and so on.

Java The development prospects

1. Become a management person, such as product development manager, Technical manager, project manager, etc.

2. Continue the path of Java technology work, become a senior software engineer, demand engineer, etc.

According to IDC statistics, in all software development talent's demand, to the Java Engineer's demand to reach the full demand 60%~70%. At the same time, Java engineers pay relatively high salaries. Java software engineers generally monthly salary range of 4000-10000 yuan, far more than the fresh graduates monthly salary of 2500 yuan average level. Generally speaking, the salary of a senior Java software engineer with one year's working experience is roughly 10.13 million of the annual salary.

Java technical training can be engaged in JSP web development, Java programming, Java game development, Java Desktop programming, and other Java language programming related work, employment is very wide.

//==============================================================

Java technology is both an advanced object-oriented programming language and a platform. Java technology is based on the concept of Java Virtual machine (Java MACHINE,JVM)-a translator between language and the underlying software and hardware. All implementations of the Java language must implement the JVM, allowing Java programs to run on any system that has a JVM.

The Java programming language (Java programming language) is unique in that Java programs are both compiled (compiled)(converted to an intermediate language called Java bytecode) and interpreted (interpreted)(the JVM parses and runs the bytecode). Compilation occurs only once, and interpretation occurs every time the program is run. The compiled bytecode uses a form of machine code optimized for the JVM, and the interpreter is the implementation of the JVM.

The Java platform (Java platform) is a pure software platform that can run on a variety of hardware-based platforms. It has three versions (see Multiple versions of the Java platform later). It consists of the JVM and Java application programming interfaces (Java application Programming Interface,api). The Java API is a large, off-the-shelf software component (Class) collection that simplifies the development and deployment of applets and applications, including robust, secure, interoperable enterprise applications. It covers everything from basic objects to networking and security to XML generation and WEB services. Java APIs are organized into libraries of related classes and interfaces, and libraries are also known as packages.

In addition to the Java API, each complete Java platform implementation includes:

• Development tools for compiling, running, monitoring, debugging applications, and building application documentation.
• A standard mechanism for deploying applications.
• A user interface toolkit that is used to create a complex graphical user interface (GUI).
• An integrated library for enabling database access and manipulating remote objects.

Java technology was originally developed by Sun Microsystems Corporation. Java Community Process (JCP, an open organization of Java developers and licensed personnel from around the world) develops and amends Java technical specifications, reference implementations, and technical compatibility packs. In August 2006, Sun Microsystems announced its intention to open the source code for the Java platform and began to solicit feedback on the licensing agreement and the way it was administered.

Why is Java technology important?
The main benefit of the Java language is that Java applications can be ported across hardware platforms and operating systems because the JVM installed on each platform can understand the same bytecode.
The Java language and platform are highly scalable. At the low end, existing applications can easily adapt to memory resources with limited equipment. This language is the ideal framework for server-side WEB programming. Because it is designed to operate over the network in a safe way, it provides a degree of security when operating over the Internet. In essence, Java technology extends the computing power of the user from the desktop to the Web resources. Web Components are supported by the run-time platform called the Web container (Web container), which includes request dispatch, security, concurrency, lifecycle management, and access to APIs such as naming, transactions, and e-mail. At the high end, the Java Application Server (application Server) acts as a web container for Java components, XML, and Web services that can interact with the database and provide dynamic Web content, and they also provide an application development environment for enterprise applications with transaction management, security , clustering, performance, availability, connectivity, and scalability.
The Java language is one of the first technologies to support enterprise open standards, enabling the use of XML and WEB services to share information and applications across lines of business (see the relationship between Java technology and Soa/web services below). Java technology is at the heart of many IBM product and Technology consulting Services (see the IBM Tools and products available to Java programmers below) and is an important part of IBM's development plan:
Learn more about IBM's service-oriented Architecture (SOA) initiatives and how SOA can help users build composite applications that combine features from multiple sources in the enterprise to support horizontal business processes.
IBM Business Innovation and optimization provides a comprehensive, component-based approach to strategic tuning. The solution provided is based on a flexible, extensible, open-standards-based software (including Java technology) and a hardware infrastructure.
The Java platform has three versions of the Java platform, which enables software developers, service providers, and device manufacturers to develop for specific markets:
Java SE (Java platform,standard Edition). Java SE was formerly known as J2SE. It allows you to develop and deploy Java applications that are used in desktops, servers, embedded environments, and live environments. Java SE contains classes that support Java WEB Service development and provides the foundation for Java platform,enterprise Edition (Java EE). Most Java developers use Java SE 5, also known as Java 5.0 or "Tiger" (June 2006, Java SE 6 or "Mustang" released the beta version. ）
The new feature series for Java SE 6 focuses on some of the new features of Java SE 6 in the API library.
The Tame Tiger column gives a wonderful overview of Java SE 5.
Merlin's Magic Series discusses previous versions of the Java SE platform, J2SE 1.4 or "Merlin". Many existing Java applications are based on J2SE 1.4, and most of the concepts in this series are related to Java SE 5 programming.
Java EE (Java platform,enterprise Edition). This version was formerly known as the Java EE. The Enterprise Edition helps develop and deploy portable, robust, scalable, and secure server-side Java applications. Built on the Java SE, Java EE provides Web services, component models, management, and communication APIs that can be used to implement enterprise-class service-oriented architecture (service-oriented Architecture,soa) and Web 2.0 applications.
The EE Explorer column provides knowledge about Java EE.
Embark on the open road: Migrating to the Java Platform Article series helps developers of. NET, Windows client/server, and ASP applications migrate to the Java EE platform.
Java ME (Java platform,micro Edition). This version was formerly known as J2ME. Java ME provides a robust and flexible environment for applications running on mobile devices and embedded devices such as mobile phones, PDAs, TV set-top boxes, and printers. Java ME includes a flexible user interface, robust security model, many built-in network protocols, and rich support for Web and offline applications that can be dynamically downloaded. Applications based on the Java ME specification need to be written once, can be used for many devices, and can take advantage of the native capabilities of each device.
This comprehensive four-part series contains two tutorials and two companion articles that focus on J2ME and Mobile information Device profile (MIDP).
You can also find many J2ME references in the DeveloperWorks Wireless technology zone, such as the two-part tutorial "Building a flexible J2ME mobile application."

//=====================

Many years ago, when I was self-taught, I was very dazed, asked questions on the Internet, always a bunch of layman said difficult ah, you need to do so, otherwise, a bunch of people say some empty words, more read more write, buy books, I have no language, in addition to some of their own ideas?
First of all, many people think that learning Java to the basis of C, but actually do not, learn to drive, I do not want to learn to ride a bicycle, there is no need.

First stage:
1. Java syntax and basics, including loops: And the related content of the class, such as implementation, inheritance, etc.
2. You need to master a few key points of the collection, the list interface of the two subclass Linkedlist,arraylist; then the two sub-classes of the Map Hashmap,hashtable;set interface Mastering list after the set is easy To master the difference between collection and collections.
3. Master IO Chapter, focus on a few flow inputstream,ouputstream; Bufferedreader,bufferedwrite;
ObjectInputStream, Objectoutputstream,,printwriter,filereader,filewriter understand the serialization of Java, master the Java file class
4. JDBC is very important, focusing on connection,preparedstatement, Statement,resultset,
Others can be learned in a study or project if they meet again, but the early emphasis is on the front few, others understand enough,
Database recommended for beginners with MySQL, download navicat for MySQL management tool
5. If you want to get started quickly, then you need to skip these,
Includes: threading, network programming, GUI programming

Okay, now you can go to phase two.

1. Html+javascript Needless to say, master how much to see oneself grasp, css do understand
2. Jsp+servlet, you need to focus on a few, request,response,session, followed by application.

Also you need to know the difference between redirect,forward, the life cycle of the servlet, etc.
3. Label aspects: (1) Master El Expression, (2) It is best to master the JSTL tag, will not, but if the JSP tag is mastered, learning Jstl is also very simple, focusing on iterative labels and formatting tags,
4. Learn Ajax, simply click on the line, without further research
5. Master the above, you can continue to learn the framework: Struts2.0;hibernate3;spring 2.0
6. If you do it above and you do 2 to 3 projects in the meantime, OK, you can go to work.
It's just a little bit of guidance for new people, not everything Java needs to learn.

What is Java? What can Java do?