Java Learning notes Java How to get started quickly

2. What is Java?

   1. Java is a high-level computer language that has been introduced in May 1995 by Sun Corporation (now acquired by Oracle) to write cross-platform applications.

   2. Sun's division of Java into three technology platforms

      1. javase--Standard Edition, mainly for the development of ordinary desktop and business applications. Javase is the core of three platforms, including the core class libraries of Java, such as collections, IO, database connections, and network programming.

      2. javaee--Enterprise Edition provides solutions for developing enterprise-class applications. The platform is used to develop, assemble, and deploy enterprise-class applications, including Servlets, JSPs, JavaBean, JDBC, EJB, WebService, and other technologies

      3. javame--Small Edition for the development of electronic consumer products and embedded devices to provide solutions. It is mainly used for the development of software programs on small digital electronic devices, such as small games on early mobile phones, intelligent control of household appliances and networking functions.

4. What are the features of the Java language?

   1. Simple

   2. Object oriented

   3. Safety

   4. Cross-platform

   5. Support Multithreading

6. JDK and JRE

   1. Jdk:java development tools, which are available to Java developers including: compilation tools, interpreters, document authoring tools, packaging tools, and more

   2. The Jre:java operating environment, equivalent to the operating system, provides the basic requirements of the Java Runtime and many basic classes of Java, such as: IO, GUI, network class, etc.

8. Path and Classpath

   1. Path: A kind of environment variable, used to save a series of executable file path, when running an executable file, the operating system will first in the current directory look for the existence of the file, if not present, the PATH environment variable defined by the paths to find the file, if not found, the system will error

   2. Classpath: is also a kind of environment variable, used to save the path of a series of class files, when the Java virtual machine executes a class file, it will first find the class file in the file defined by the CLASSPATH environment variable, if it does not exist, it will look in the current directory, if not found, The system will get an error.

10. Operating mechanism of Java

    1. Compile-the compiler compiles a well-written Java program to generate a class file (bytecode file)

    2. Class load--java virtual machines load compiled class files into memory

    3. Explanation Execution--java Virtual machine interpretation execution for Java classes loaded into memory

12. Jvm

    The JVM (Java Virtual machine) is a specification for computing devices, a fictional computer that is implemented by simulating various computer functions on a real computer.

    Java programs are interpreted by the virtual machine, not the operating system, which reflects the Java cross-platform a bit, different operating systems need to use different versions of the virtual machine, to solve the different operating system compiled by different machine code problems. Greatly reduces the cost of program development and maintenance.

Java programs implement cross-platform features through the JVM, but Java virtual machines are not cross-platform, meaning that the JVM on different operating systems is different.

7. Configuration of environment variables

Open My Computer Properties-------Advanced system settings-------environment variables

-----New-----Variable name in the system variable: Java_home Variable Value: Installation path for JDK

Locate the path in the system variable------precede with "%java_home%\bin;" or, at the very end, add ";%java_home%\bin" (Note that the semicolon must be an English input method)

This article is from the "Five Piglets" blog, please be sure to keep this source http://wuxiaozhu.blog.51cto.com/7942143/1757221

Java Learning notes Java How to get started quickly