import java.util.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.table.*;
  
/**
 * @version 1.0 11/09/98
 */
public class MultiLineHeaderExample extends JFrame {
  MultiLineHeaderExample() {
    super( "Multi-Line Header Example" );
 
    DefaultTableModel dm = new DefaultTableModel();
    dm.setDataVector(new Object[][]{{"a","b","c"},
                                    {"A","B","C"}},
                     new Object[]{"1st\nalpha","2nd\nbeta","3rd\ngamma"});
 
    JTable table = new JTable( dm );
    MultiLineHeaderRenderer renderer = new MultiLineHeaderRenderer();
    Enumeration enum = table.getColumnModel().getColumns();
    while (enum.hasMoreElements()) {
      ((TableColumn)enum.nextElement()).setHeaderRenderer(renderer);
    }   
    JScrollPane scroll = new JScrollPane( table );
    getContentPane().add( scroll );
    setSize( 400, 110 );
    setVisible(true);
  }
 
  public static void main(String[] args) {
    MultiLineHeaderExample frame = new MultiLineHeaderExample();
    frame.addWindowListener( new WindowAdapter() {
      public void windowClosing( WindowEvent e ) {
        System.exit(0);
      }
    });
  }
}

import java.io.*;
import java.util.*;
import java.awt.*;
import javax.swing.*;
import javax.swing.table.*;


/**
 * @version 1.0 11/09/98
 */
public class MultiLineHeaderRenderer extends JList implements TableCellRenderer {
  public MultiLineHeaderRenderer() {
    setOpaque(true);
    setForeground(UIManager.getColor("TableHeader.foreground"));
    setBackground(UIManager.getColor("TableHeader.background"));
    setBorder(UIManager.getBorder("TableHeader.cellBorder"));
    ListCellRenderer renderer = getCellRenderer();
    ((JLabel)renderer).setHorizontalAlignment(JLabel.CENTER);
    setCellRenderer(renderer);
  }
 
  public Component getTableCellRendererComponent(JTable table, Object value,
                   boolean isSelected, boolean hasFocus, int row, int column) {
    setFont(table.getFont());
    String str = (value == null) ? "" : value.toString();
    BufferedReader br = new BufferedReader(new StringReader(str));
    String line;
    Vector v = new Vector();
    try {
      while ((line = br.readLine()) != null) {
        v.addElement(line);
      }
    } catch (IOException ex) {
      ex.printStackTrace();
    }
    setListData(v);
    return this;
  }
}