Answers for "how to add an option to quit while program is running java"

install composer on linux

# The following method has been tested on Ubuntu 20.04
# But i think it should work fine with any other distribution

# Ensure you're on Desktop, to prevent issues with permissions
cd ~/Desktop

# Download the installer script
php -r "copy('https://getcomposer.org/installer', 'composer-setup.php');"

# Verify intergrity to check whether an error happened during the fetch
php -r "if (hash_file('sha384', 'composer-setup.php') === '8a6138e2a05a8c28539c9f0fb361159823655d7ad2deecb371b04a83966c61223adc522b0189079e3e9e277cd72b8897') { echo 'Installer verified'; } else { echo 'Installer corrupt'; unlink('composer-setup.php'); } echo PHP_EOL;"

# Download composer script, which is the actual composer file
php composer-setup.php

# Remove the installer script as it's no longer needed
php -r "unlink('composer-setup.php');"

# To use composer globally, it's a good idea to move it to the path
# /usr/local/bin
sudo mv composer.phar /usr/local/bin/composer

# Try running composer to see if everything works fine
composer -V
# If you see the following output, then you're good to go:
# Composer version 1.10.10 2020-08-03 11:35:19

composer install ubuntu

sudo curl -s https://getcomposer.org/installer | phpmixed

java quit application

System.exit(n);