Initial knowledge of Java learning -002-java

This article focuses on what is Java, and Java Common sense knowledge, to facilitate the parents to further understand the Java language-related common sense.

First, Java overview

The Java language is the object-oriented programming language introduced by Sun Microsystems Corporation in 1995, which takes into account the characteristics of the Internet era and is suitable for the development of the Internet. The Java-enabled HotJava browser (Java Applet support) shows the potential of Java: cross-platform, dynamic WEB, Internet computing. In the design of cross-platform, security, object-oriented and other characteristics received the majority of programming enthusiasts love, but also become a number of corporate programming language preferred. In addition, many of the open-source testing tools now have Java figure (such as jmeter,selenium, etc.).

Java is the Java object-oriented programming language (hereinafter referred to as the Java language) and Java platform introduced by Sun Microsystems Company, and is a pure object-oriented programming language.

The Java platform consists of a Java virtual machine (Java VM) and a Java application Programming interface (application Programming Interface, API). The Java application Programming Interface provides a standard operating system-independent interface for Java applications, enabling the Java language to implement cross-platform.

Second, Java can be divided into the following three systems:

2. javase (Java Platform,Standard Edition,java Edition). 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).
4. java EE (platform,enterprise Edition,java Enterprise Edition). 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.
6. javame (Java platform,micro Edition,java Mobile device edition). 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.

Third, the characteristics of the Java language:

Java is an excellent programming language, is a simple, object-oriented, distributed, interpreted, robust, secure, platform-independent (cross-platform), architecture-neutral, portable, high-performance, multi-threading, automatic memory management, dynamic language.

2. simplicity of: Java is a simple and easy to learn language. Its syntax is very close to the C and C + + languages, is easier to learn and use, and discards the seldom-used, difficult-to-understand, confusing features of C + +, such as operator overloading, multiple inheritance, and so on. In addition, the Java language no longer uses pointers, and provides an automatic garbage collection processing mechanism, so that programmers do not have to worry about memory management.
4. Object-oriented: Java is an object-oriented language, and for Java everything is an object. The Java language provides primitives such as classes, interfaces, and inheritance, supports only single inheritance between classes, supports multiple inheritance between interfaces, and supports the implementation mechanism between classes and interfaces (the keyword is implements). The Java language fully supports dynamic binding, and C + + supports dynamic binding of virtual functions only. If you understand the basic concepts of Java object-oriented, learning Java will be much easier.
6. Distributed: Java can be applied to distributed internet environments. The Java language supports the development of Internet applications, and there is a network application programming interface (java.net) in the basic Java application programming interface, which provides a class library for network application programming, including URLs, URLConnection, sockets, ServerSocket and so on. The RMI (remote method Activation) mechanism of Java is also an important tool for developing distributed applications.
8. Explanatory type: Java programs are compiled into bytecode format on the Java platform and can be run on any system that implements the Java platform. At runtime, these bytecode are interpreted by the Java interpreter in the Java platform, and the classes required during execution are loaded into the runtime environment during the connection phase.
10. Robustness: Java mainly by the compile time and run-time error check, to the extent possible to exclude unknown errors. Java's strong type mechanism, exception handling, garbage automatic recovery mechanism, security check mechanism and so on are the important guarantee of Java program robustness.
12. Security: The Java language provides a security mechanism to prevent malicious code from attacking. In addition to the many security features of the Java language, Java has a security mechanism (class ClassLoader) for classes that are downloaded over the network, such as assigning different namespaces to prevent substitution of local names, byte code checks, and providing security management mechanisms (class SecurityManager) becomes a security guarantee for Java. Java's security features ensure that Java can be used to develop virus-free, hard-to-tamper systems. The authentication technology of Java is based on public key cryptography.
14. platform agnostic: The Java language is not designed to be specific to a particular platform structure, unlike a programming language such as C + +. At compile time, Java programs are compiled into byte codes that are independent of the specific architecture. Bytecode can be published on the Internet and interpreted by the Java virtual machine (JVM).
16. Architecture Neutrality: The Java compiler generates platform-independent bytecode format files (files with the suffix CALSS) that can be run on any system that implements the Java platform and is suitable for heterogeneous network environments and software distribution.
18. portability: derived from architectural neutrality. The Java language is platform agnostic, and the Java language Specification does not stipulate any specific implementation-related content, which makes Java portable. Compilers and Java are written in ANSI C language based on the limitations of POSIX portability.
    
20. High performance: Java is high-performance compared to interpreted advanced scripting languages. At the same time, with the rapid development of JIT (JUST-IN-TIME) Instant compilation technology, Java will have high performance features.
22. Multithreading: Java supports multithreaded programming, and Java allows you to write programs that perform multiple tasks at the same time. This feature allows developers to build stable, interactive applications.
24. Dynamic Nature: Java is a language that is more dynamic than C + + and adapts to changing environments. Java programs can carry a large amount of runtime information that is used to validate and parse run-time objects.

Initial knowledge of Java learning -002-java