title: How do I enable X11 display on Ubuntu 20.04? (I have it installed locally)
body: <p>Any time I'd like to run a file that opens a window, I get the following error:</p>
  <p>No X11 DISPLAY variable was set, but this program performed an operation which requires it.
  at java.desktop/java.awt.GraphicsEnvironment.checkHeadless(GraphicsEnvironment.java:208)
  at java.desktop/java.awt.Window.(Window.java:548)
  at java.desktop/java.awt.Frame.(Frame.java:423)
  at java.desktop/java.awt.Frame.(Frame.java:388)
  at java.desktop/javax.swing.JFrame.(JFrame.java:180)
  at hw04.GameOfLife.(GameOfLife.java:23)
  at hw04.GameOfLife.main(GameOfLife.java:147)</p>
  <p>EDIT: I ran sudo apt-get install libx11-dev and it says I already have it installed... I don't know where to go from here</p>