Ao iniciar o netbeans a partir do terminal, o seguinte erro é recebido.
rishabh@rishabh-HP-Notebook:~$ netbeans
WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by org.netbeans.ProxyURLStreamHandlerFactory (file:/opt/netbeans/platform/lib/boot.jar) to field java.net.URL.handler
WARNING: Please consider reporting this to the maintainers of org.netbeans.ProxyURLStreamHandlerFactory
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release
Eu tive o mesmo problema ao tentar usar o NetBeans 8.1 com o Java 9. Se java -version disser 1.9, você poderá fazer o downgrade para 1.8 algo assim:
# Install Java 8 if you don't already have it.
sudo apt install openjdk-8-jdk
# Switch to Java 8
sudo update-alternatives --config java
# Attempt to run Netbeans again.
netbeans