Java? __java

One: what is Jvva.

1.Java is an object-oriented programming language.

2.Java is not only a programming language on which applications can be developed and run on the Internet or in the enterprise's internal network

The 3.Java Development Toolkit (JDK&JRE) is a complete set of tools for developing, debugging, compiling, and running Java programs : Java application area. 1. Distribution of three major systems:

The Java platform has three versions, enabling software developers, service providers, and device manufacturers to develop for specific markets:

(1): 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. The Java SE contains classes that support Java WEB Service development and provides a foundation for Java platform,enterprise Edition (Java EE).
(2): Java EE (Java platform,enterprise Edition). This version was formerly called Java EE. The enterprise version helps develop and deploy portable, robust, scalable, and secure server-side Java applications. Java EE is built on the basis of Java SE, which provides Web services, component models, management, and communication APIs that can be used to implement enterprise-class service-oriented architectures (service-oriented Architecture,soa) and Web 2.0 applications.
(3): Java ME (Java platform,micro Edition). This version was formerly known as J2ME. The 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. The Java ME includes a flexible user interface, robust security model, many built-in network protocols, and rich support for networking and offline applications that can be downloaded dynamically. Applications that are based on the Java ME specification are written once, can be used with many devices, and can take advantage of the native capabilities of each device.References: HTTP://ZHIDAO.BAIDU.COM/QUESTION/46247870.HTML?FR=QRL Three: The characteristics of Java 1.Java is a simple, object-oriented, distributed, interpreted, robust, secure, structurally neutral, portable, efficient, multi-threaded and dynamic language 2.Java's important features: Cross-platform, object-oriented, open source 3.Java Important mechanism JVM Garbage Collection Four: Introduction to the JVM 1.Java virtual Machine (JVM) is the abbreviation of Java Virtual machine, refers to the use of hardware or software means to implement virtual computers. Java Virtual machine has its own perfect hardware architecture, such as processor, stack, register and so on, but also has the corresponding instruction system 2.Java source code and byte code are not machine-independent 3.JVM is machine-related and is installed on different operating system machines and requires a JVM developed specifically for the operating system The JVM can be viewed as a virtual computer system that can run Java bytecode, and he has a parser component that enables communication between Java bytecode and computer operating systems. Five: Garbage collection 1. In C + +, programmers need to manage their own memory, Java provides a system-level thread to track memory allocations, and memory areas that are no longer used will be automatically recycled 2. Different implementations of the JVM, garbage collection mechanism very different 3. If you need to make an object recyclable, you must remove all references on it, usually by placing it null 4. However, even with the garbage collection mechanism, there may still be a memory overflow situation VI: Writing the first Java program using the editor to write Java source programs Source FileName: Main class name. Java Compiling source code into bytecode using the compiler byte-code filename: source filename. class run with virtual machine (interpreter) work process: Load, code checksum, interpret execution commands that must be mastered skillfully javac Command: The compiler compiles Java source files into bytecode files java command: JVM interprets execution of a compiled bytecode file switch to the directory where the *.java file is located through cmd, compile the *.java source file with the Javac command, and run the application using the Java command.