Java review--initial knowledge of Java

1. Initial knowledge of Java

1. What is Java?

Java is a computer language, which is a high-level language and is a high-level language introduced by Sun Corporation (acquired by Oracle Corporation) in 1995.

to enable software developers to develop for specific markets, Sun Company divides Java into three technology platforms, namely Javase, Java EE, javame

Javase (Java Platform standard Edition), a solution for developing common desktop applications, Javase is the most central part of three platforms, and Java EE and javame have been developed from the basis of javase, The Javase platform includes Java's core class libraries, such as collections, Io, and so on.

Java Platform Enterprise Edition is a solution for developing enterprise-class applications, including Servlets, JSPs, JavaBean, and other technologies

Javame (Java Platform Micro Edition) Small edition is a solution for the development of electronic consumer products and embedded devices. For example, add smart controls for home appliances, add new game features to your phone

2. Features of the Java language

simple, safe, cross-platform features .

3. Install JDK( Focus )

can be downloaded and installed from the official address jdk:http://www.oracle.com/technetwork/java/javase/downloads/index.html, but when downloading the installation, you need to be aware of the correspondence between the operating system (OS) version and the JDK version, As shown:

Figure -5

Directory after installation:

? bin Directory: This directory is used to store executable programs such as Javac.exe(java compiler),java.exe(Java Runtime tool),Jar.exe (packaging tools) and Javadoc.exe(document generation tools).

? DB Directory: is a pure Java Implementation, open source database management system. This database is not only lightweight, but also supports all the specifications of the JDBC 4.0, when learning jdbc, there is no need to install additional database software, you can choose to use the JAVADB directly

? include Directory: because JDK is implemented through C and C + + , so you need to introduce some C -Language header files at startup, which is used to store these header files.

? JRE Catalogue : This directory is the root directory of the Java Runtime Environment JRE, containing the Java virtual machine, the runtime's class package, theJava Application Launcher, and a bin directory, It does not include development tools in the development environment.

? Lib directory:Lib is the abbreviation for the library, meaning the Java class library or library file, which is the archive package file used by the development tool.

? Src.zip file:src.zip is a compressed file of src folder,the source code of the JDK core class is placed in src , and the file can be viewed in Java the source code for the underlying class.

JDK comes with JRE and public JRE difference: public JRE is for ordinary computer users, if you install a Java program, this Java program will invoke the JRE (Java Runtime Environment) when it starts to run If you are a Java developer, then you need to install the JDK, and when you develop the Java program you will invoke the JRE in the JDK.

4.Java compilation run process

Java programmers write files with the suffix of. Java, which the operating system does not recognize correctly, so it is first compiled to generate so-called bytecode files (. Class), and bytecode files require the JVM to provide support for the running environment.

The JVM is a software that is installed in the operating system and is built on top of the operating system, providing a running environment for bytecode files .

Java review--initial knowledge of Java