Reading a comma delimited file (CSV) using the regex package

Use the method Pattern.split which creates an array of strings around your regular expression.

Main.java:

import java.util.regex.*;
import java.io.*;
 
public class Main
{
   public static void main(String []args) throws Exception {
      if (args.length != 1) {
         System.err.println("Usage: java Main filename.csv");
         System.exit(1);
      }
 
      Pattern p = Pattern.compile(",");
 
      BufferedReader br = new BufferedReader(new FileReader(args[0]));     
      String line = null;
      while ((line = br.readLine()) != null) {
         String[] arr = p.split(line); 
         for (int i=0; i<arr.length; i++) {
            System.out.print("t" + arr[i]);
         } 
         System.out.println();
      }
      br.close();
   }
}

Example CSV file, test.csv:

OrionServer,20.03,190.9,1000
WebLogic,190.22,234.2,93244
WebSphere,223.59,32.2,283
JBoss Server,33,44,55

Output:

	OrionServer	20.03	190.9	1000
	WebLogic	190.22	234.2	93244
	WebSphere	223.59	32.2	283
	JBoss Server	33	44	55

Alternatively, you can use the method split that was introduced in the String class since 1.4.

Main.java:

import java.io.*;
 
public class Main
{
   public static void main(String []args) throws Exception {
      if (args.length != 1) {
         System.err.println("Usage: java Main filename.csv");
         System.exit(1);
      }
 
      BufferedReader br = new BufferedReader(new FileReader(args[0]));     
      String line = null;
      while ((line = br.readLine()) != null) {
         String[] arr = line.split(","); 
         for (int i=0; i<arr.length; i++) {
            System.out.print("t" + arr[i]);
         } 
         System.out.println();
      }
      br.close();
   }
}

Compressing using the GZIP algorithm at runtime in Java

Use the standard API class GZIPOutputStream. Internally, it uses Deflater to compress data. The following example asks the user a file to compress and writes the compressed stream of data to file.gzip. If you want to compress multiple files to the same outputstream, you need to call finish to write the remaining compressed data without closing the stream. Otherwise, call close.

Main.java:

import java.util.zip.*;
import java.io.*;
 
public class Main {
   public static void main(String args[]) {
      if (args.length != 1) {
         System.out.println("Usage: java Main <file>");
         System.out.println("<file>.gzip will be created");
         System.exit(1);
      }
 
      try {
         FileInputStream fis = new FileInputStream(args[0]);
         FileOutputStream fos = new FileOutputStream(args[0] + ".gzip");
 
         GZIPOutputStream gos = new GZIPOutputStream(fos); 
         byte []buffer = new byte[1024];
         int l;
         while ((l = fis.read(buffer)) >= 0) {
            gos.write(buffer, 0, l);
         }
 
         // not necessary unless you want to write more files to the GZIPOutputStream
         // gos.finish();  
         gos.close();
         fis.close();
      }
      catch(IOException e) {
         System.out.println(e);
      }
   }
}

Getting events when a JOptionPane is closing

Embed your JOptionPane in a dialog and add a PropertyChangeListener.

Main.java:

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.beans.*;
  
public class Main
{
   public static void main(String []args) {
      JFrame frame = new JFrame();
 
      final JOptionPane pane = new JOptionPane("Are you sure you want to import this file?n" +
                                               "(try presssing the x button!)", 
                                               JOptionPane.QUESTION_MESSAGE,
                                               JOptionPane.YES_NO_CANCEL_OPTION);
      final JDialog dialog = new JDialog(frame, "Question", true);
      dialog.setContentPane(pane);
  
      dialog.addWindowListener(new WindowAdapter() {
         public void windowClosing(WindowEvent we) {
            pane.setValue(new Integer(JOptionPane.CLOSED_OPTION));
         }
      });
 
      pane.addPropertyChangeListener(new PropertyChangeListener() {
         public void propertyChange(PropertyChangeEvent e) {
            String prop = e.getPropertyName();
            if (dialog.isVisible() 
             && (e.getSource() == pane)
             && (prop.equals(JOptionPane.VALUE_PROPERTY) ||
                 prop.equals(JOptionPane.INPUT_VALUE_PROPERTY)))
            {
               System.out.println("Caught, JOptionPane is ready to close!");
               dialog.setVisible(false);
            }
         }
      });
 
      dialog.pack();
      dialog.setVisible(true);
      Object value = pane.getValue();
      System.out.println("Option " + value + " selected!");
      
      System.exit(1);
   }
}

Creating a scrollable JPanel

Create a JScrollPane and pass your panel to its constructor. Then add the scrollpane to the container. Make sure your panel has a size in case you use the null layout manager (with setSize and setPreferredSize). Here’s an example that uses a BorderLayout.

Main.java:

import java.awt.event.*;
import javax.swing.*;
import java.awt.*;
 
public class Main extends JFrame
{
   public Main() {
      getContentPane().setLayout(new BorderLayout());
 
      JPanel panel = createPanel();
 
      getContentPane().add(BorderLayout.CENTER, new JScrollPane(panel));
 
      addWindowListener(new WindowAdapter() {
         public void windowClosing(WindowEvent we) {
            System.exit(0);
         }
      });
   }
 
   public static JPanel createPanel() {
      JPanel panel = new JPanel();
      panel.setLayout(new GridLayout(20, 4, 10, 10));
 
      for (int i=0; i<20; i++) {
         for (int j=0; j<4; j++) {
            JLabel label = new JLabel("label " + i + ", " + j);
            label.setFont(new Font("Helvetica", Font.PLAIN, 30));
            panel.add(label);            
         }
      }
 
      return panel;
   }
 
   public static void main(String [] args) {
      Main main = new Main();
      main.setSize(300, 300);
      main.setVisible(true);
   } 
} 

Creating a scrollable JTabbedPane

Starting from JDK1.4, you can set the tab layout policy to either WRAP_TAB_LAYOUT or SCROLL_TAB_LAYOUT, for example:

      tabbedPane.setTabLayoutPolicy(JTabbedPane.SCROLL_TAB_LAYOUT);

Main.java:

import java.awt.event.*;
import javax.swing.*;
import java.awt.*;
import java.net.*;
 
public class Main extends JFrame implements ActionListener {
   JTabbedPane tabbedPane;
   int ntabs = 0;
 
   public Main() {
      getContentPane().setLayout(new BorderLayout());
      tabbedPane = new JTabbedPane();
      tabbedPane.setTabLayoutPolicy(JTabbedPane.SCROLL_TAB_LAYOUT);
 
      createTab();
 
      getContentPane().add(BorderLayout.CENTER, tabbedPane);
      setJMenuBar(createMenuBar());
  
      addWindowListener(new WindowAdapter() {
         public void windowClosing(WindowEvent we) {
            System.exit(0);
         }
      });
   
      setTitle("JTabbedPane Scrollable Demonstration");
      setSize(new Dimension(400, 400));
   }
 
   protected JMenuBar createMenuBar() {
      JMenuBar menuBar = new JMenuBar();
 
      JMenu menu1 = new JMenu("JTabbedPane");
      JMenuItem menuItem1 = new JMenuItem("Create new tab");
      menuItem1.addActionListener(this);
      menu1.add(menuItem1);
      JMenu menu2 = new JMenu("Change orientation");
      JMenuItem menuItem2 = new JMenuItem("TOP");
      menuItem2.addActionListener(this);
      menu2.add(menuItem2);
      JMenuItem menuItem3 = new JMenuItem("BOTTOM");
      menuItem3.addActionListener(this);
      menu2.add(menuItem3);
      JMenuItem menuItem4 = new JMenuItem("LEFT");
      menuItem4.addActionListener(this);
      menu2.add(menuItem4);
      JMenuItem menuItem5 = new JMenuItem("RIGHT");
      menuItem5.addActionListener(this);
      menu2.add(menuItem5);
      menuBar.add(menu1);
      menuBar.add(menu2);
 
      return menuBar;
   }
  
   public void actionPerformed(ActionEvent e) {
      if (e.getActionCommand().equals("Create new tab")) {
         createTab();
      }
      else if (e.getActionCommand().equals("TOP")) {
         tabbedPane.setTabPlacement(JTabbedPane.TOP);
      }
      else if (e.getActionCommand().equals("BOTTOM")) {
         tabbedPane.setTabPlacement(JTabbedPane.BOTTOM);
      }
      else if (e.getActionCommand().equals("LEFT")) {
         tabbedPane.setTabPlacement(JTabbedPane.LEFT);
      }
      else if (e.getActionCommand().equals("RIGHT")) {
         tabbedPane.setTabPlacement(JTabbedPane.RIGHT);
      }
   }
 
   protected void createTab() {
      ntabs++;
      tabbedPane.addTab("Tab #" + ntabs, new JLabel("Tab #" + ntabs));
   }
 
   public static void main(String []args) {
      Main main = new Main();
      main.show();
   }
}

Adding a vertical line separator to a JToolBar

The method addSeparator in the JToolBar class only adds blank space. You could add JSeparator components to your JToolBar with add but then you run into trouble when changing the orientation. In the following example, this has been solved by listening to propertyChangeEvents and changing the JSeparator orientation so that they are opposite to the JToolBar’s orientation.

Main.java:

import javax.swing.border.*;
import java.awt.event.*;
import javax.swing.*;
import java.beans.*;
import java.awt.*;
  
public class Main extends JFrame {
   public Main() {
      super("JToolBar example");
 
      final JTextArea textArea = new JTextArea(5, 30);
      MyJToolBar toolBar = new MyJToolBar();
 
      JButton gifButton = new JButton(new ImageIcon("gifIcon.gif"));
      JButton jpgButton = new JButton(new ImageIcon("jpgIcon.gif"));
      JButton tiffButton = new JButton(new ImageIcon("tiffIcon.gif"));
 
      gifButton.addActionListener(new ActionListener() {
         public void actionPerformed(ActionEvent ae) {
            textArea.append("gifButton clicked!n");
         }
      });
  
      jpgButton.addActionListener(new ActionListener() {
         public void actionPerformed(ActionEvent ae) {
            textArea.append("jpgButton clicked!n");
         }
      });
        
      tiffButton.addActionListener(new ActionListener() {
         public void actionPerformed(ActionEvent ae) {
            textArea.append("tiffButton clicked!n");
         }
      });
 
      toolBar.add(gifButton);
      toolBar.add(new JToolBar.Separator());
      toolBar.add(new JSeparator(JSeparator.VERTICAL));
      toolBar.add(new JToolBar.Separator());
      toolBar.add(jpgButton);
      toolBar.add(new JToolBar.Separator());
      toolBar.add(new JSeparator(JSeparator.VERTICAL));
      toolBar.add(new JToolBar.Separator());
      toolBar.add(tiffButton);
 
      addWindowListener(new WindowAdapter() {
         public void windowClosing(WindowEvent e) {
            System.exit(0);
         }
      });
 
      getContentPane().setLayout(new BorderLayout());
      getContentPane().add(BorderLayout.NORTH, toolBar);
      getContentPane().add(BorderLayout.CENTER, new JScrollPane(textArea));
   }
 
   public static void main(String[] args) {
      Main main = new Main();
      main.setSize(300, 300);
      main.setVisible(true);
   }
}
 
class MyJToolBar extends JToolBar
{
   public MyJToolBar() {
      super();
      listenForOrientationChange();
   }
 
   public MyJToolBar(int orientation) {
      super(orientation);
      listenForOrientationChange();
   }
 
   public MyJToolBar(String name) {
      super(name);
      listenForOrientationChange();
   }
 
   public MyJToolBar(String name, int orientation) {
      super(name, orientation);
      listenForOrientationChange();
   }
 
   protected void listenForOrientationChange() {
      addPropertyChangeListener(new PropertyChangeListener() {
         public void propertyChange(PropertyChangeEvent evt) {
            MyJToolBar toolBar = MyJToolBar.this;
            Component[] components = toolBar.getComponents();
            for (int i=0; i<components.length; i++) {
               if (components[i] instanceof javax.swing.JSeparator) {
                  JSeparator separator = (JSeparator) components[i];
                  if (toolBar.getOrientation() == SwingConstants.HORIZONTAL) {
                     separator.setOrientation(JSeparator.VERTICAL);      
                     separator.setMaximumSize(new Dimension(2,
                                              toolBar.getPreferredSize().width));
                  }
                  else {
                     separator.setOrientation(JSeparator.HORIZONTAL);
                     separator.setMaximumSize(new Dimension(
                                              toolBar.getPreferredSize().height, 2));
                  }
               }
            }
         }
      });
   }
}

Programmatically closing a JInternalFrame

Use this:

   frame.getDesktopPane().getDesktopManager().closeFrame(frame);

Main.java:

import java.awt.event.*;
import javax.swing.*;
import java.util.*;
import java.awt.*;
import java.net.*;
 
public class Main extends JFrame {
   JDesktopPane desktop;
   int nframes = 0;
 
   JMenu internalFrameMenu;
   Action closeAction = new CloseAction();
 
   public Main() {
      desktop = new JDesktopPane(); 
      setContentPane(desktop);
      setJMenuBar(createMenuBar());
      createInternalFrame(); 
      addWindowListener(new WindowAdapter() {
         public void windowClosing(WindowEvent we) {
            System.exit(0);
         }
      });
   }
 
   protected JMenuBar createMenuBar() {
      JMenuBar menuBar = new JMenuBar();
 
      JMenu createMenu = new JMenu("Create");
      createMenu.setMnemonic(KeyEvent.VK_C);
      JMenuItem newMenuItem = new JMenuItem("New");
      newMenuItem.addActionListener(new ActionListener() {
         public void actionPerformed(ActionEvent ae) {
            createInternalFrame();
         }
      }); 
      newMenuItem.setMnemonic(KeyEvent.VK_N);
      createMenu.add(newMenuItem);
      menuBar.add(createMenu);
 
      internalFrameMenu = new JMenu("Close");
      internalFrameMenu.setMnemonic(KeyEvent.VK_C);
  
      menuBar.add(internalFrameMenu);     
 
      return menuBar;
   }
 
   protected void createInternalFrame() {
      nframes++;
      String title = "JInternalFrame #" + nframes;
      JInternalFrame frame = new JInternalFrame(title,
         true,    // resizable
         true,    // closable
         true,    // maximizable
         true);   // iconifiable
      frame.setVisible(true); 
      desktop.add(frame);
      frame.setSize(200, 200);
      frame.setLocation(30*nframes, 30*nframes);
      try {
         frame.setSelected(true);
      } catch (java.beans.PropertyVetoException e) {}
 
      JMenuItem menuItem = new JMenuItem(title);
      internalFrameMenu.add(menuItem);
      menuItem.addActionListener(closeAction);
      frames.put(title, frame);
   }
 
   public static void main(String []args) {
      Main main = new Main();
      main.setSize(500, 300);
      main.setVisible(true);
   }
 
   public class CloseAction extends AbstractAction
   {
      public CloseAction() {
         super("Close Action");
      }
 
      public void actionPerformed(ActionEvent ae) {
         JMenuItem menuItem = ((JMenuItem) ae.getSource());
         JInternalFrame frame = (JInternalFrame) frames.get(menuItem.getText());
         // close the frame
         frame.getDesktopPane().getDesktopManager().closeFrame(frame);
         // remove JMenuItem from JMenu
         JMenu parent = (JMenu) ((JPopupMenu) menuItem.getParent()).getInvoker();
         parent.remove(menuItem);
      }
   }
}

Assinging a shortcut key to a JButton

Swings JButton inherits from AbstractButton that defines a method setMnemonic.
You can use it as follows:

import javax.swing.event.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.*;
import java.awt.*;
   
public class Main extends JFrame
{
   public Main() throws Exception {
      JButton button = new JButton("Click or press ALT-C");
      button.setMnemonic('C');
 
      getContentPane().add(button);
      pack();
 
      button.addActionListener(new ActionListener() {
         public void actionPerformed(ActionEvent evt) {
            System.out.println("Button clicked!");
         }
      });
 
      addWindowListener(new WindowAdapter() {
         public void windowClosing(WindowEvent e) {
            System.exit(0);
         }
      });
   }
 
   public static void main(String args[]) throws Exception {
      Main main = new Main();
      main.show();
   }
}

Invoking a JPopupMenu from a JComboBox

Add a MouseListener:

import java.awt.event.*;
import javax.swing.*;
import java.util.*;
import java.awt.*;
    
public class Main extends JFrame
{ 
   public Main() {
      getContentPane().setLayout(new FlowLayout());
      
      final JComboBox combobox = new JComboBox(new String[] { "Item 1", "Item 2", "Item 3" });
      final JPopupMenu popup = new JPopupMenu();
      JMenuItem mi1 = new JMenuItem("Popup Item 1");
      JMenuItem mi2 = new JMenuItem("Popup Item 2");
      popup.add(mi1);
      popup.add(mi2);
 
      ((JButton) combobox.getComponent(0)).addMouseListener(new MouseAdapter() {
         public void mousePressed(MouseEvent me) {
            if (me.isPopupTrigger()) {
               popup.show(combobox, me.getX(), me.getY());
            }
         }
 
         public void mouseReleased(MouseEvent me) {
            if (me.isPopupTrigger()) {
               popup.show(combobox, me.getX(), me.getY());
            }
         }
      });
 
      getContentPane().add(combobox);
  
      addWindowListener(new WindowAdapter() {
         public void windowClosing(WindowEvent we) {
            System.exit(1);
         }
      });      
   
      setSize(new Dimension(200, 200));
   } 
 
   public static void main(String[] args) throws Exception {
      Main main = new Main();
      main.setVisible(true);
   }
}

Changing the color of every element in a JList

Customize the CellRenderer as in following example:

import javax.swing.event.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.*;
import java.awt.*;
  
public class Main extends JFrame {
 
   public Main() {
      getContentPane().setLayout(new FlowLayout());
 
      Vector v = new Vector();
      final JList list = new JList(
         new Colorable[] { new ColoredItem("Item 1", Color.yellow),
                           new ColoredItem("Item 2"),
                           new ColoredItem("Item 3", Color.blue),
                           new ColoredItem("Item 4", Color.red),
                           new ColoredItem("Item 5", Color.green)
                         });
 
      list.setCellRenderer(new ColoredCellRenderer());
      getContentPane().add(new JScrollPane(list));    
 
      addWindowListener(new WindowAdapter() {
         public void windowClosing(WindowEvent event) {
            System.exit(0);   
         }      
      });
 
      setSize(200, 300);
   }
   
   public static void main(String[] args) {
      (new Main()).show();
   }
}
 
class ColoredCellRenderer extends DefaultListCellRenderer implements ListCellRenderer {
   public Component getListCellRendererComponent(
      JList list, Object value, int index, boolean isSelected, boolean cellHasFocus)    
   {
      setText((value == null) ? "" : value.toString());
      Color c = ((Colorable) value).getColor();
      if (isSelected) {
         setBackground(list.getSelectionBackground());
         setForeground(c);
      }
      else {
         setBackground(list.getBackground());
         setForeground(c);
      }
 
      setEnabled(list.isEnabled());
      setFont(list.getFont());
 
      return this;
   }
}
 
class ColoredItem implements Colorable {
   Object  object;
   Color   color;
                            
   public ColoredItem(Object object, Color color) {
      this.object = object;
      this.color = color;
   }
                             
   ColoredItem(Object object) {
      this(object, Color.black);
   }
 
   public Color getColor() {
      return color;
   } 
 
   public void setColor(Color color) {
      this.color = color;
   }                           
                            
   public String toString() {
      return object.toString();
   }
}
                         
interface Colorable {
   public Color getColor();
   public void setColor(Color c);
}