OpenJDK 21 : インストール2024/06/21

	OpenJDK 21 をインストールします。
[1]	OpenJDK 21 のインストールと動作確認です。

root@dlp:~#

apt -y install openjdk-21-jdk

root@dlp:~#

cat > /etc/profile.d/java.sh <<'EOF'
export JAVA_HOME=$(dirname $(dirname $(readlink $(readlink $(which java)))))
export PATH=$PATH:$JAVA_HOME/bin
EOF

root@dlp:~#

source /etc/profile.d/java.sh

root@dlp:~#

java --version

openjdk version "21.0.3" 2024-04-16
OpenJDK Runtime Environment (build 21.0.3+9-Ubuntu-1ubuntu1)
OpenJDK 64-Bit Server VM (build 21.0.3+9-Ubuntu-1ubuntu1, mixed mode, sharing)

# テストプログラムを作成して動作確認

root@dlp:~# cat > java_test.java <<'EOF'
class java_test {
    public static void main(String[] args) {
        System.out.println("Hello Java World !");
    }
}
EOF

root@dlp:~#

javac java_test.java

root@dlp:~#

java java_test

Hello Java World !

[2]	公式リポジトリから複数バージョンをインストールしている場合は [update-alternatives] で切り替え可能です。

root@dlp:~#

update-alternatives --config java

There are 4 choices for the alternative java (providing /usr/bin/java).

  Selection    Path                                            Priority   Status
------------------------------------------------------------
  0            /usr/lib/jvm/java-21-openjdk-amd64/bin/java      2111      auto mode
  1            /usr/lib/jvm/java-11-openjdk-amd64/bin/java      1111      manual mode
* 2            /usr/lib/jvm/java-17-openjdk-amd64/bin/java      1711      manual mode
  3            /usr/lib/jvm/java-21-openjdk-amd64/bin/java      2111      manual mode
  4            /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java   1081      manual mode

Press <enter> to keep the current choice[*], or type selection number: 3
update-alternatives: using /usr/lib/jvm/java-21-openjdk-amd64/bin/java to provide /usr/bin/java (java) in manual mode

root@dlp:~#

update-alternatives --config javac

There are 4 choices for the alternative javac (providing /usr/bin/javac).

  Selection    Path                                          Priority   Status
------------------------------------------------------------
  0            /usr/lib/jvm/java-21-openjdk-amd64/bin/javac   2111      auto mode
  1            /usr/lib/jvm/java-11-openjdk-amd64/bin/javac   1111      manual mode
* 2            /usr/lib/jvm/java-17-openjdk-amd64/bin/javac   1711      manual mode
  3            /usr/lib/jvm/java-21-openjdk-amd64/bin/javac   2111      manual mode
  4            /usr/lib/jvm/java-8-openjdk-amd64/bin/javac    1081      manual mode

Press <enter> to keep the current choice[*], or type selection number: 3
update-alternatives: using /usr/lib/jvm/java-21-openjdk-amd64/bin/javac to provide /usr/bin/javac (javac) in manual mode

root@dlp:~#

java -version

openjdk version "21.0.3" 2024-04-16
OpenJDK Runtime Environment (build 21.0.3+9-Ubuntu-1ubuntu1)
OpenJDK 64-Bit Server VM (build 21.0.3+9-Ubuntu-1ubuntu1, mixed mode, sharing)

root@dlp:~#

javac -version

javac 21.0.3