[Java] Build Java development environment on Ubuntu & check execution

environment

Ubuntu VSCode

things to do

--Java, Maven, Intellij installation --vscode settings --Execution confirmation --Error handling

reference

This is very helpful!

Installation

Please note that apt update, java installation and java version check are performed together below.

Java

Installation

sudo apt update && sudo apt install default-jdk && java -version

openjdk version "11.0.6" 2020-01-14
OpenJDK Runtime Environment (build 11.0.6+10-post-Ubuntu-1ubuntu118.04.1)
OpenJDK 64-Bit Server VM (build 11.0.6+10-post-Ubuntu-1ubuntu118.04.1, mixed mode)

JAVA_HOME setting

Since the installation location of jdk is in / usr / lib / jvm /, add this path to the 〇〇rc file.

~/.〇〇rc file

# ------------------------------------------------------------------
# java
# ------------------------------------------------------------------
export JAVA_HOME=/usr/lib/jvm/java-version-xxx-jdk
export PATH="$PATH:$JAVA_HOME/bin"

Maven

Installation

sudo apt update && apt install maven && mvn -version

Apache Maven 3.6.0
Maven home: /usr/share/maven
Java version: 11.0.6, vendor: Ubuntu, runtime: /usr/lib/jvm/java-11-openjdk-amd64
Default locale: ja_JP, platform encoding: UTF-8
OS name: "linux", version: "4.15.0-54-generic", arch: "amd64", family: "

IntelliJ IDEA Community Edition

Installation

① From PPA

sudo add-apt-repository ppa:mmk2410/intellij-idea-community
sudo apt update
sudo apt install intellij-idea-community

② From the software center

Search with intellij and click install

VSCode

Installation

wget -q https://packages.microsoft.com/keys/microsoft.asc -O- | sudo apt-key add -

sudo add-apt-repository "deb [arch=amd64] https://packages.microsoft.com/repos/vscode stable main"

sudo apt update && sudo apt install code

VS Code settings

Extensions

Java Extension Pack ――Put this in without thinking. --The minimum required tools for Java development will be installed together. https://marketplace.visualstudio.com/items?itemName=vscjava.vscode-java-pack

Code Runer

--You can debug the selected range. --You can run Code Runner with Ctrl + Alt + N.

https://marketplace.visualstudio.com/items?itemName=formulahendry.code-runner

settings.json

• java.home You will be able to run JAVA on VS Code.

• maven.executable.path Maven commands can now be executed on VS Code.

• code-runner.runInTerminal Enables CodeRunner input / output with terminal.

~~code-runner.executorMap code runner Sets the run-time command. With the default settings, the target file is considered to have no fileNameWithoutExt extension, so an error (java.lang.NoClassDefFoundError) may occur depending on where the debug is executed. This can be avoided by using $ fileName ~~

Find out the execution path of maven

which mvn
> /usr/bin/mvn

settings.json

[
  // Java
  "java.home":"/usr/lib/jvm/java-version-xxx-jdk",

  // Maven
  "maven.executable.path": "/usr/bin/mvn",

  // Code Runner
  "code-runner.runInTerminal": true,
]

Execution confirmation

--Use VS Code. --Create an appropriate directory and create a HelloWorld.java file. --The part where the main method is located is debugged.

Main method public static void main(String[] args) Be sure to describe this.

~/java_lessons/hello_java/HelloWorld.java

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

Run

Either of the following can be executed. Compile & run.

--Run with Code Runner (Ctrl + Alt + N)

• Run > Start Debugging ( F5 )

[Done] exited with code=1 in 1.227 seconds

[Running] cd "/home/user/java_lessons/hello_java/" && javac HelloWorld.java && java HelloWorld

Hello World!

Without the main method It will be as follows.

error:The main method cannot be found in class HelloWorld. Define the main method as follows:
   public static void main(String[] args

Error example

Remedy etc.

The compiler compliance specified is x.x but a JRE x.y is used

Match the corresponding number in .settings/org.eclipse.jdt.core.prefs to the JRE version

eclipse.preferences.version=1
org.eclipse.jdt.core.compiler.codegen.targetPlatform= x.y
org.eclipse.jdt.core.compiler.compliance= x.y
org.eclipse.jdt.core.compiler.problem.enablePreviewFeatures=disabled
org.eclipse.jdt.core.compiler.problem.forbiddenReference=warning
org.eclipse.jdt.core.compiler.problem.reportPreviewFeatures=ignore
org.eclipse.jdt.core.compiler.processAnnotations=disabled
org.eclipse.jdt.core.compiler.release=disabled
org.eclipse.jdt.core.compiler.source= x.y

Recommended

You can try it out!