import javax.swing.JTextPane;
import javax.swing.text.Style;
import javax.swing.text.StyleConstants;
import javax.swing.text.StyledDocument;
public class Main {
public static void main(String[] argv) throws Exception{
JTextPane textPane = new JTextPane();
StyledDocument doc = (StyledDocument) textPane.getDocument();
// Create a style object and then set the style attributes
Style style = doc.addStyle("StyleName", null);
StyleConstants.setFontSize(style, 30);
doc.insertString(doc.getLength(), "Some Text", style);
}
}