week 2019 9:16

First, what is the programming language

1, the language can be divided into two categories:

Natural language - communication tool between people

For example: Chinese, English, Japanese, Korean and so on;

Programming languages ​​- Tools and computer programmers to communicate

For example: c, c ++, c #, jave, net, python and so on;

2, software development model

Front-end development: developed for web (b) or client software (c) of

Web development language -HTML, CSS, JaceScript and other
client development languages -C, C ++, Android, ISO etc.

Back-end development: the positive development of the back-end server (s) of

Common server development languages: jave, C #, NET, Python, etc.

4, each programming language applications

>    C语言用于编写计算机底层开发，主要编写计算机操作系统、系统软件；
 >  C++语言适用于多种类型的开发，主要用于编写PC客户端软件，如：QQ、爱奇艺、迅雷等；并且C++还是大型游戏（单机游戏、网游）开发的首选，如：魔兽、LOL、PUBG；
  >  Android、IOS语言主要编写移动端软件；
  >  Java、C#、.NET语言主要用于编写大型服务器后台开发，其中Java占据主导地位，Java还是大数据库开发、物联网开发、云计算开发等领域的基础性语言；
  >  php语言主要用于编写中小型网站后台；
  >  Python语言主要用于自动化服务器运维、自动化测试、数据分析、人工智能等领域；

5, Java language origin and development

• In 1995, Sun's James Goasling (Java father), who developed a C-based language developed specifically for the site, named Java (formerly known as Oak language);
• In 1996, Sun JDK1.0 company developed software was nearly tens of thousands of websites use Java technology, the same year ten major operating system vendors declare their products directly embedded Java technology. sun company held the first "JavaOne Conference" in San Francisco, the conference is the world's millions of Java programmers annual technology event;
• In 1998, JDK1.2, Java technology and will be subdivided into three directions:
• J2SE (Java SE) ------------- desktop software development
• J2EE (Java EE) ------------- enterprise-class server development
• J2ME (Java ME) ----------- mobile device development technology, derived from the latter part of the direction of Android
• In 2006, JDK6.0 birth (Java SE6.0, Java EE6.0, Java ME6.0);
• In 2009, Oracle acquired Sun Microsystems, Java language all owned by Oracle;
• In 2011, Java 7.0;
• 2014, Java 8.0;
• 2017, Java 9.0;
• March 2018, Java 10;

• September 2018, Java 11;

  6, Java development and employment orientation?

  Employment orientation:
  
  the Java programmers to develop the direction of development:
  
  the Java programmer to select the direction:
  

  7、JDK

  JDK is the Java development environment software, is available to, included in Java JDK and JRE Java development tools used by programmers to start the program;
  the JRE is the Java runtime environment, Java programs are available to the user for use, JRE included JVM and system libraries. Wherein JVM is the Java virtual machine, the virtual machine is to provide support for Java bytecode runtime files required; system libraries (Java source code) is a common feature of Java-written in advance, directly used in the use of it can be used.
  

  7.1, the role of the JDK ---- cross-platform (systems, servers) to develop and run

  C language compilation process: .c source code file, directly after the compiler to generate 0 and 1

  QQ: C language to write the
  Windows version of QQ ------------ only run on a Windows system
  Linux version of QQ ---------------- - you can only run on a Linux system
  IOS version of the QQ -------------------- only run on IOS system
  software using C language it, a system It corresponds to a separate version of the software. Because different operating systems 0 and 1 for parsing compiled is different:
  Windows version 10101010 QQ ------------
  Linux version of QQ ------------ 01010101 ------
  IOS version of the QQ --------------------- 11110000

Java language compilation process:
1) the source .java files, after compiled Java byte code files (.class);
2) loading the JVM (0 and 1) and the byte code files

Assuming that QQ is written in Java: Java version of QQ, QQ after the compiler generates bytecode files:

Windows版的JDK------------运行在Windows系统上
Linux版的JDK-----------------运行在Linux系统上
IOS版的JDK-------------------运行在IOS系统上

7.2、JDK的安装和配置

桌面右击“计算机”----“属性”----“高级系统设置”----“环境变量”

7.2.2、JDK的配置内容

• 新建一个名为JAVA_HOME的变量

  变量名：JAVA_HOME
  变量值：电脑中JDK的安装路径，指向JDK文件夹
  

• 修改path中的内容

  path变量中规定内容是系统的所有可执行程序的路径信息，在配置path时不要删除path中原有的内容，在配置时只能在path的前后增加新的配置，建议在path的前面配置。path中新增的JDK配置内容为：指向JDK下的bin文件夹，通常写法为：%JAVA_HOME%\bin。在具体书写时，注意bin后面必须以分号结尾，分号代表配置结果。
  

  7.3、JDK环境的检测

  Windows系统在CMD窗口下进行JDK的检测
  java -version：检测JAVA_HOME
  

  javac（编译工具）、java（运行工具）：检测path

  

  8、Java入门----编写第一个Java程序

  使用记事本+CMD进行Java开发，这种方式是早期Java开发的常用形式。

  1. 首先，使用记事本编写Java源代码文件
     例如：编写一个Java程序，实现输出“HelloWorld”这句话
     
     

  2. 然后，在CMD窗口下进行编译运行程序
     1、编译----javac
     语法：javac 源文件名（必须加后缀）
     
     2、运行----java
     语法：java 类名（不加后缀）
     

     9、使用eclipse进行Java开发

     eclipse 开源免费的，适用于多种语言（安装语言插件）开发的软件
     myeclipse 不开源不免费的，内置一套JDK环境
     ideas 适用于JavaEE框架开发
     NetBeans

     IBM's eclipse is spent tens of millions of funds to develop and open source software has a project in eclipse, the package, the concept of class:
     Project name ---- the equivalent of a cell
     pack ------- equivalent to the inside of the cell house unit
     class corresponds ------- floor unit inside each household

     9.1, create a Java project

     
     
     
     

     9.2, create a package in the project

     
     

     9.3, create a class in a package