Your code works fine on my machine:
import java.awt.Color;
import java.awt.FlowLayout;
import javax.swing.JEditorPane;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.WindowConstants;
import javax.swing.border.Border;
import javax.swing.border.LineBorder;
public class JEditorPaneBorderExample {
public static void main(String[] args) {
JFrame jFrame = new JFrame();
jFrame.setDefaultCloseOperation(WindowConstants.DISPOSE_ON_CLOSE);
jFrame.setSize(400, 300);
JPanel panel = new JPanel(new FlowLayout());
jFrame.setContentPane(panel);
JEditorPane editor = new JEditorPane();
new JEditorPaneBorderExample().remove_border(editor);
panel.add(editor);
jFrame.setVisible(true);
}
private Border b = new LineBorder(Color.black, 1);
void remove_border(JEditorPane com) {
com.setBorder(b);
}
}