****Java
``Computers are divided into hardware and software.
Hardware: keyboard, mouse, host, and cpu.
Note: The hardware cannot work and requires software to drive the hardware to work.
Software: application software and system software.
System software: software that directly interacts with the hardware, such as win7 ,
application software: the operating system running on the
class notes
day01
作为程序员应该掌握相关的windows的相关dos命令：
1. 在dos命令窗口中打开并编写命令
win+R输入cmd 打开后就是dos窗口
2.常见的dos命令：
exit---退出当前的dos窗口
cls----清理都是窗口的屏幕
如何复制dos窗口中的数据：
3. 点击dos窗口中任意一个位置右键，选择标记，选中要标记的内容即可
4. dir命令是列出当前目录下所有的子目录和子文件
5.cd命令：
可以完成目录的切换
cd +路径
路径包括相对路径和绝对路径
绝对路径：表示从某个磁盘的盘符作为出发点的路径
相对路径：表示从当前所在路径下作为的出发点的路径
6. cd。。 回到上级目录
cd\ 直接回到根目录
7.怎么切换盘符？
c:+回车
e:+回车
f:+回车
g:+回车
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Regarding the setting of windos, the setting of the
file extension, as a programmer, must ensure that the end of the new document must be .java (the extension is set by yourself)
2. Java outline and content
Computer programming language:
1.1 A pre-designed one Set communication rules. Sometimes, some grammars need to be memorized by rote. You don’t need to ask why, but you only need to abide by this set of language rules. Then you can communicate well with the computer. This is the computer’s Programming language.
1.2
Machine language (binary), low-level language (assembly language), high-level language,
development history:
the development history of Java and the development history of language features that are developing in a direction that is more understandable by humans
: 1995...developed by sun company, later by ooracle The company’s acquisition of
Java consists of three major areas:
JavaSE (Java Standard Edition) Basic
JavaEE (Java Enterprise Edition) Main direction
JavaME (Java Micro Edition)
Java language features: {open source, free, pure object-oriented, cross-platform}
Simplicity: Relative In terms of, for example: Java does not support multiple inheritance, C++ supports multiple inheritance, there are pointers in C++, and pointers are shielded in Java. Relatively speaking, Java is a simple Java language. The bottom layer is
an object-oriented implementation in C++ : pure object-oriented. , More in line with people's thinking mode, easier to understand.
Portability:
One-time compilation of Java language can run on Windows and Linux operating systems without any modification. This is called Java portability, or cross-platform (write once, run everywhere)
Java programs cannot directly interact with the operating system, and the principles of the operating system are different.
Using the Java virtual machine for short: jvm can deal with different operating systems
jdk Java development kit
multithreading
Robustness: related to the automatic garbage collection mechanism, the abbreviation of the automatic garbage mechanism is: the garbage generated by the gc mechanism is automatically collected.
Security
9. About the loading and execution of the Java language (important learning starts here)
9.1 The running of a Java program includes two important stages
-compilation stage
-run stage--编译阶段： 创建文件（扩展名得是.Java 如 xxx·Java (也叫源文件） 编译阶段的主要任务是检查Java的源文件是否符合Java语法，符合则能够生成正常的字节码 字节码文件不是纯粹的二进制，无法直接在操作系统中直接运行 编译阶段的编译过程： *创建一个Java文件《简称为.Java源文件》在文件中编写源代码（不能随意编写，必须符合Java规则) *Java程序员需要使用JDK中自带的Javac.exe命令进行Java程序的编译。 Javac怎么用？在那用？ -在DOS窗口中运用 -Java的使用规则： Java Java源文件的路径 *Javac是Java的编译器工具 *一个Java源文件可以生成多个.class文件 字节码文件/.class文件是最中要执行文件，所以说class文件生成之后，Java源文件的删除并不会影响 Java程序的执行 编译结束后可以将Java文件拷贝到其他你的操作系统中进行运行