Java study prelude daysof01

Let's talk a few nonsense words before you start. The prelude to Java learning has actually been read yesterday. However, it was very late. So I didn't sort out my notes in time. The Java prelude provides a few simple lessons.

The first is the definition of software development. Software development is a collection of computer data and commands organized in a specific order. Therefore, the role of software is to make human-computer interaction better. Software classification includes system software and application software.

The second is to explain in detail how to use related commands in the doscommand line. DOS is the initial interface of Windows systems. due to complicated operations and poor user experience, the following graphic interface Windows system appears. However, DOS still inherits from windows. It is also used sometimes. To cope with some common operations, there are some common commands: ① dir: list files and folders in the current directory; ② CD: enter a specific object; ③ CD ..: return the parent directory; ④ CD ..: return the parent directory; ⑤ Exit: exit the DOS interface.

The third point is the Java language. Java is one of the computer languages. It is an object-oriented Solution invented by jamesgosling under sun (Stanford University Network ).Programming Language. Since the popularity of the Internet in 1995, Java has been very popular since then. Java sets three branch architectures: J2EE (JAVA Platform Enterprise Edition), j2se (Java platform Standard Edition), and j2( Java platformmicro Edition). After jdk1.5, It is renamed javaee, the same is true for the other two. The reason why the Java language is very popular is that Java can run across platforms. The so-called "cross-platform" means that Java can run on different operating systems, such as Windows, Linux, and Mac. Then you may want to ask why cross-platform access is allowed? The principle is to install JVM (Java Virtual Machine) on the system platform, and the JVM will explain and execute JavaProgram. Therefore, from the definition of the principle, we know that Java programs run on JVM, while JVM is relatively platform-specific. It cannot be cross-platform.

the first thing to learn a language is to configure the language environment. There are two names in the Java environment: JDK and JRE. JRE is a Java runtime environment that includes the core class libraries required by JVM and Java programs. JDK (Java Development Kit) is used by programmers, including development tools and running JRE. You can configure the environment variables. There are two configuration methods. One is temporary configuration (in the doscommand line) and the other is configured in the System Properties dialog box.
currently, two environment variables need to be configured. Add a java_home environment variable:
You can also add a java_home environment variable before the path value
.
there are a lot of related environment variable configurations on the Internet. At first, I found resources from the Internet. Since the environment has been configured, is there an impulse to write a program. Development tools are required to develop programs. If you are good enough, you can use Notepad for development. Of course, at first I used notepad for development. Because the developed program is very simple, I can still bear it with notepad. Now that the network is so developed, those who love computers should have some powerful notebooks. Just select what you like. A simple Java Source Code is:

Note the following points for this class: ① JavaCodeThey are all embodied in the form of classes, and classs is a Java keyword to indicate classes. ② The Java program runs from the main function. ③ Java is case-sensitive, and Class are irrelevant. ④ The suffix of the Java source program is. java. After the program is written, the compiler must compile the program. The environment variables have been configured before, so you only need to go to the directory where the source program is located and execute javac demo. java. After compiling, an oke will appear in this directory. class file, which is run by JVM. class file. After running the command: Java demo, you will see hello
World.

The last question is annotations. Many languages have the following format: single-line comment (Format: //) and multi-line comment (/**/). Multi-line comment cannot be nested. A special annotation in Java is a document annotation (/***/).

My Mind Map:

 

 

PS: As Mr. Bi said, the more questions he will learn, the more he will eventually learn. If there is something wrong with it, please check it out. Hey hey ·····

A lot of nonsense. I thought it was useless, and there were a lot of details left empty. But the main thing is here.