[LINUX] [Latest] How to build Java environment on Ubuntu

1. Prior knowledge

-[Super easy] How to install VirtualBox on Windows -[2019 latest] How to create an Ubuntu virtual environment with VirtualBox

As prior knowledge, the contents of the above link are required.

2. What is Java?

―― Java is a class-based object-oriented programming language, which is characterized by being generic and ʻOS independent. -- Java is a fast and reliable language in terms of security. --The advantage of choosing Java is that it is used in a wide range of areasdue to its high reliability, and it has abundantlibraries and so on`.

3. Advance preparation

#Add repository
$ sudo add-apt-repository ppa:webupd8team/java

#Get the package list from the repository
$ sudo apt-get update

Start ʻOracle VM VirtulaBox and start the virtual machine`.
Start command line.
Enter the above code.

4. Install JRE

#Install JRE
$ sudo apt-get install openjdk-6-jre
$ sudo apt-get install openjdk-7-jre
$ sudo apt-get install openjdk-8-jre

Select one of the above version and enter the command.

5. Install the JDK

#Install the JDK
$ sudo apt install openjdk-6-jdk
$ sudo apt install openjdk-7-jdk
$ sudo apt install openjdk-8-jdk

Enter the command same version as the version selected in` 3. Install JRE``.

6. Java verification

`Hello.java`


public class Hello{
   public static void main(String[] args){
     System.out.println("Hello World!!");
   }
}

Start File and right-click.
Click New Folder and change Folder Name to Java.
Confirm that the folder has been created and start the text editor.
Enter the above source code in the text editor and click the save button.
Enter Hello.java as the file name and click the Save button.
Start command line and enter the code below.

#Move to Java folder
$ cd Java

# Hello.Compile java
$ javac Hello.java

#Run
$ java Hello

If Hello World !! is displayed as shown in the image, it is successful.

7. Code that is useful to know

#java version check
$ java -version

#javac version check
$ javac -version

#Java management
$ sudo update-alternatives --config java

#Javac management
$ sudo update-alternatives --config javac

-- java -version can check the version of java. --javac -version allows you to check the version of javac. -- sudo update-alternatives --config java allows you to manage multiple java versions. --sudo update-alternatives --config javac allows you to manage multiple javac versions`.