Java BASICS (1): Java webjava

Java BASICS (1): Java webjava

1. Java Overview

JavaEE refers to Java Enterprise Edition and Java Enterprise Edition, which are mostly used for Enterprise-level development, including web development. It is also called J2EE.

JavaSE generally refers to Java Standard Edition and Java Standard Edition, which is the development of general Java programs (such as desktop programs) and can be considered as a subset of JavaEE.

Java is a language, and J2EE is a technology used in Java. Java provides libraries and syntaxes for J2EE. J2EE uses Java libraries and syntaxes applied to the WEB. This is a conceptual difference.

More detailed explanation:

The Java platform has three versions, allowing software developers, service providers, and device manufacturers to develop for specific markets:
Java SE (Java Platform, Standard Edition ). Java SE is previously called J2SE. It allows the development and deployment of Java applications used in the desktop, server, embedded environment, and real-time environment. Java SE Contains classes that support Java Web service development and provides the foundation for Java Platform and Enterprise Edition (Java EE.
Java EE (Java Platform, Enterprise Edition ). This version was previously called J2EE. The Enterprise Edition helps develop and deploy portable, robust, scalable, and secure server-side Java applications. Java EE is built on the basis of Java SE. It provides Web Services, component models, management and communication APIs, and can be used to implement enterprise-level service-oriented architecture (service-oriented architecture, SOA) and Web 2.0 applications.
Java ME (Java Platform, Micro Edition ). This version was previously known as j2-based. Java ME provides a robust and flexible environment for applications running on mobile devices and embedded devices (such as mobile phones, PDAs, TV set-top boxes, and printers. Java ME includes flexible user interfaces, robust security models, many built-in network protocols, and rich support for dynamic download of network connections and offline applications. Applications Based on Java ME specifications can be used on many devices only once, and the local functions of each device can be used.

Ii. Common doscommands

The doscommand is a command used in the DOS console. the pop-up method of the DOS console is win + R, and then the cmd command is output.

　　

There are many doscommands, which are commonly used in Java. The content is as follows:

1. Clear screen: cls;

When there are too many contents in the DOS console, you can use the clear screen command, which is equivalent to "wiping the blackboard ";

For example, C: \> cls, and then press Enter.

2. Switch the drive letter ::;

By default, the drive C is used. If you want to remove another drive letter, you can use this command;

For example, C: \> E:, and then press enter to go to the drive E.

Enter the specified directory: cd;

This command can be used to access a directory;

For example, D :\> cd develop, which enters the D: \ develop directory. Of course, you must ensure that this directory exists;

For example, D :\> cd develop \ Java, and then enter the D: \ develop \ Java directory.

3. Return to the directory at the upper level: cd...; 0

This command can be used when you need to return to the upper-level directory;

For example, D: \ develop \ Java> cd..., and press enter to return to the D: \ develop directory.

4. Return the drive letter root directory: cd \;

You can use this command to return to the root directory of the current drive letter;

For example, D: \ develop \ Java> cd \, and press enter to return to the D:/directory.

5. display the file and subdirectory information in the current directory: dir;

You can use this command to view all files and subdirectories in the current directory;

6. Run the application: complete program name Parameters

This command can be used to run an application;

For example, to run the Notepad program: D: \> C: \ windows \ notepad.exe, open the Notepad program: \ double-click the program icon under the windows directory has the same effect, because the program supports double-click operation;

You can also omit the suffix ".exe", for example, D: \> C: \ windows \ notepad. The effect is the same as above;

Iii. Differences between JDK and JRE

JDK: it is a Java Development and running environment. JDK must be installed on a programmer's computer;

JRE: Java Runtime Environment. It is a Java Runtime Environment. If you do not need to develop a Java program, you can install JRE. For example, a program developed by a programmer is finally sold to the user, and the user does not need to develop, but only needs to run the program, so the user can install JRE on the computer.

JDK contains JRE.

Iv. cross-platform features of JAVA

The Platform refers to the Operating System (Windows, Linux, Mac ).

Java programs can be run on any operating system.

Java Virtual Machine (JVM)

 

V. Hello World case

 

1 public class HelloWorld{2     public static void main(String[] args){3         System.out.println("Hello  World!!!");4     }5 }

We can understand that the program is roughly as follows;