import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTabbedPane;
import javax.swing.JTextArea;



public class Main {

	static JTextArea area01, area02;
	private static JTabbedPane tabbedPane;
	private static JPanel tab;	
	
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		
		JFrame frame = new JFrame(); 
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(270,270);
        
        tabbedPane = new JTabbedPane(JTabbedPane.TOP);
		
		tabbedPane.setBounds(10, 10, 250, 250);
		frame.getContentPane().add(tabbedPane);
		
        tab = new JPanel(null);
        tabbedPane.addTab("Пример", tab);
        
        
        area01 = new JTextArea();
        area01.setLayout(null);
        area01.setBounds(20, 20, 200, 20);
        area01.getDocument().addDocumentListener(new ContentJTextAreaListener());
        tab.add(area01);
        
        area02 = new JTextArea();
        area02.setLayout(null);
        area02.setBounds(20, 50, 200, 20);
        area02.getDocument().addDocumentListener(new ContentJTextAreaListener());
        tab.add(area02);
        
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
	}

import javax.swing.JTextArea;
import javax.swing.event.DocumentEvent;
import javax.swing.event.DocumentListener;

public class ContentJTextAreaListener implements DocumentListener {

	@Override
	public void insertUpdate(DocumentEvent e) {
		// TODO Auto-generated method stub
		updateLog(e, "inserted into");
	}

	@Override
	public void removeUpdate(DocumentEvent e) {
		// TODO Auto-generated method stub
		updateLog(e, "inserted into");
	}

	@Override
	public void changedUpdate(DocumentEvent e) {
		// TODO Auto-generated method stub

	}
	
	public void updateLog(DocumentEvent e, String action) {

		System.out.println("ContentJTextAreaListener updateLog : " + e.getLength());
	}

}