Change the orientation of a JTextArea, eg. right to left

You can use the method setComponentOrientation defined in the Component class, so
you can invoke it on most Swing components.
It does not seem to work properly using JDK1.2, but does with JDK1.3.

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 {
      JTextArea tf = new JTextArea();
      getContentPane().add(tf);
      pack();

      tf.setComponentOrientation(ComponentOrientation.RIGHT_TO_LEFT);
 
      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();
   }
}

For international applications, you can determine the orientation using
the Locale:

      Locale arabic = new Locale("ar", "SA");
      jcomponent.setComponentOrientation(ComponentOrientation.getOrientation(arabic));

Creating a formatted textfield that only accepts IP addresses

JDK1.4 introduced the JFormattedTextfield with which you can set a mask on a text field.
This example not only shows you how to set the mask (eg. 255.255.xxx.xxx), but also how to use an InputVerifier to check whether the inputted digits lie in the range [0-255].

Main.java:

import javax.swing.JFormattedTextField.*;
import javax.swing.text.*;
import java.awt.event.*;
import javax.swing.*;
import java.text.*;
import java.util.*;
import java.awt.*;
 
public class Main extends JFrame 
{
   public Main() throws Exception
   {
      addWindowListener(new WindowAdapter() {
         public void windowClosing(WindowEvent we) {
            System.exit(1);
         }
      });
 
      MaskFormatter formatter = new MaskFormatter("255.255.###.###");
      formatter.setPlaceholderCharacter('0');
 
      final JFormattedTextField formattedTf = new JFormattedTextField(formatter);
      formattedTf.setInputVerifier(new IPTextFieldVerifier());
 
      final JTextField normalTf = new JTextField(25);
      JButton button = new JButton("Get value");
      button.addActionListener(new ActionListener() {
         public void actionPerformed(ActionEvent ae) { 
            normalTf.setText(""+formattedTf.getValue());
         }
      });
 
      getContentPane().setLayout(new FlowLayout(FlowLayout.LEFT));
      getContentPane().add(formattedTf);
      getContentPane().add(button);
      getContentPane().add(normalTf);
 
      formattedTf.setPreferredSize(normalTf.getPreferredSize());
   }
  
   public static void main(String args[]) throws Exception 
   {
      Main main = new Main();
      main.setSize(300, 150);
      main.setVisible(true);
   }
}
 
class IPTextFieldVerifier extends InputVerifier {
   public boolean verify(JComponent input) {
      if (input instanceof JFormattedTextField) {
         JFormattedTextField ftf = (JFormattedTextField)input;
         AbstractFormatter formatter = ftf.getFormatter();
         if (formatter != null) {
            String text = ftf.getText();
            StringTokenizer st = new StringTokenizer(text, ".");
            while (st.hasMoreTokens()) {
               int value = Integer.parseInt((String) st.nextToken());
               if (value < 0 || value > 255) {
                  // to prevent recursive calling of the 
                  // InputVerifier, set it to null and
                  // restore it after the JOptionPane has
                  // been clicked.
                  input.setInputVerifier(null);
                  JOptionPane.showMessageDialog(new Frame(), "Malformed IP Address!", "Error", 
                                                JOptionPane.ERROR_MESSAGE);
                  input.setInputVerifier(this);  
                  return false;
               }
            }
            return true;
         }
      }
      return true;
   }
 
   public boolean shouldYieldFocus(JComponent input) {
      return verify(input);
   }
}

Aligning the drop-down arrow of a JComboBox to the right

Main.java:

import java.awt.event.*;
import javax.swing.*;
import java.awt.*;
 
public class Main extends JFrame
{
   public Main() {
      this.addWindowListener(new WindowAdapter() {
         public void windowClosing(WindowEvent we) {
            System.exit(0);
         }
      });
 
      getContentPane().setLayout(new FlowLayout(FlowLayout.LEFT));
      Object []items = new Object[] { "one", "two", "three", "four", 
                                      "five", "six", "seven" };
      JComboBox comboBox = new JComboBox(items);
      getContentPane().add(comboBox);
      comboBox.setComponentOrientation(ComponentOrientation.RIGHT_TO_LEFT);
   }
 
   public static void main(String []args) {
      Main main = new Main();
      main.setSize(200, 200);
      main.setVisible(true);
   }
}

Compile Java contained in a String

A bit of hacking around lead to the following example. Create an instance of InMemorySourceCompiler and pass it the name of the program and the source code as a String. Any suggestions/improvements are appreciated as a comment to this answer.

The following example creates a JFrame that contains the output of the source.

Main.java:

import java.lang.reflect.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.*;
import java.util.*;
import java.io.*;
  
import sun.tools.javac.*;  
import sun.tools.java.*;
   
public class Main extends JFrame
{
   public Main(String s) {
      getContentPane().add(new JTextArea(s, 3, 50));
      addWindowListener(new WindowAdapter() {
         public void windowClosing(WindowEvent we) {
            System.exit(1);
         }
      });
   }
  
   public static void main(String args[]) throws Exception
   {
      // Save all data written to System.out to a byte array and display in frame
      PrintStream ps = System.out;
      ByteArrayOutputStream baos = new ByteArrayOutputStream();
      System.setOut(new PrintStream(baos));
 
      InMemorySourceCompiler imsCompiler = new InMemorySourceCompiler("Test",
          "public class Test {" +
          "   public static void main(String args[]) {" +
          "      System.out.println("Output of program:");" +
          "      for (int i=0; i<10; i++) {" +
          "         System.out.println(i);" +
          "      }" +
          "      System.out.println("End of output.");" + 
          "   }" +
          "}");
      imsCompiler.executeMain();
 
      byte[] b = baos.toByteArray();
 
      System.setOut(ps);
 
      String s = new String(b);
 
      Main main = new Main(s);
      main.setSize(200, 230);
      main.setVisible(true);  
   }
}
       
class InMemorySourceCompiler {
   protected String name;
   protected String source;
   protected Class compiledClass;
  
   public InMemorySourceCompiler(String name, String source) throws Exception {
      this.name = name;
      this.source = source;
      loadClass();
   }
 
   protected void loadClass() throws Exception {
      ClassPath cp = new ClassPath(System.getProperty("java.class.path"));
      OutputStream os = System.out;
      BatchEnvironment be = new BatchEnvironment(os, cp);
      be.flags = 0x41004;
      be.majorVersion = 45;
      be.minorVersion = 3;
      be.covFile = null;
      be.setCharacterEncoding(null);
 
      be.parseFile(new InMemorySourceClassFile(name+".java", source));
 
      ByteArrayOutputStream baos = new ByteArrayOutputStream(4096);
 
      be.flushErrors();
      Vector v = new Vector();
 
      for (Enumeration enum = be.getClasses(); enum.hasMoreElements();) {
         v.addElement(enum.nextElement());
      }
 
      for (int i=0; i<v.size(); i++) {
         ClassDeclaration cd = (ClassDeclaration) v.elementAt(i);
         Object object = cd.getClassDefinition(be);
 
         if (object instanceof SourceClass) {
            SourceClass sourceclass = (SourceClass) object;
            cd.setDefinition(sourceclass, 5);
            SourceClass sourceclass1 = (SourceClass) object;
            baos.reset();
            sourceclass.compile(baos);
         }
         else if (object instanceof BinaryClass) {
            BinaryClass binaryclass = (BinaryClass) object;
            binaryclass.write(be, baos);
         }
         byte[] b = baos.toByteArray();
 
         InMemorySourceCompilerClassLoader myClassLoader = new InMemorySourceCompilerClassLoader();
         compiledClass = myClassLoader.getClassFromBytes(name, b);
      }
   }
 
   public void executeMain() throws Exception {
      Method m = compiledClass.getMethod("main", new Class[]{ String[].class });
      m.invoke(null, new Object[]{null});
   }
 
   static class InMemorySourceCompilerClassLoader extends ClassLoader
   {
      public Class getClassFromBytes(String name, byte[] b) {
         return defineClass(name, b, 0, b.length);
      }
   }
}
 
class InMemorySourceClassFile extends ClassFile
{
   private String filename;
   private String text;
 
   public InMemorySourceClassFile(String filename, String text) {
      super(new File(filename));
      this.filename = filename;
      this.text = text;
   }
 
   public String getAbsoluteName() {
      return filename;
   }
 
   public boolean exists() {
      return true;
   }
 
   public InputStream getInputStream() {
      return new StringBufferInputStream(text);
   }
 
   public String getName() {
      return filename;
   }
 
   public String getPath() {
      return "";
   }
 
   public boolean isDirectory() {
      return false;
   }
 
   public boolean isZipped() {
      return false;
   }
  
   public long lastModified() {
      return new Date().getTime();
   }
 
   public long length() {
      return text.length();
   }
 
   public String toString() {
      return filename;
   }
}

Changing the margins of a JToolBar

Set an empty border on your JToolBar object.

Main.java:

import javax.swing.border.*;
import java.awt.event.*;
import javax.swing.*;
import java.awt.*;
  
public class Main extends JFrame {
   public Main() {
      super("JToolBar example");
 
      final JTextArea textArea = new JTextArea(5, 30);
      JToolBar toolBar = new JToolBar();
 
      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(jpgButton);
      toolBar.add(tiffButton);
 
      toolBar.setBorder(new EmptyBorder(new Insets(10,10,10,10)));
 
      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);
   }
}

images used:


Capturing a close event on a JInternalFrame

Main.java:

import java.awt.event.*;
import javax.swing.*;
import java.beans.*;
import java.util.*;
import java.awt.*;
import java.net.*;
 
public class Main extends JFrame {
   JDesktopPane desktop;
   int nframes = 0;
  
   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);
 
      return menuBar;
   }
 
   protected void createInternalFrame() {
      nframes++;
      String title = "JInternalFrame #" + nframes;
      MyJInternalFrame frame = new MyJInternalFrame(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) {}
   }
 
   public static void main(String []args) {
      Main main = new Main();
      main.setSize(500, 300);
      main.setVisible(true);
   }
} 
 
class MyJInternalFrame extends JInternalFrame 
                       implements VetoableChangeListener { 
   public MyJInternalFrame(String title, boolean resizable, 
                           boolean closable, boolean maximizable, 
                           boolean iconifiable) { 
      super(title, resizable, closable, maximizable, iconifiable); 
      addVetoableChangeListener(this); 
   } 
 
   public void vetoableChange(PropertyChangeEvent pce) 
                                 throws PropertyVetoException { 
      if (pce.getPropertyName().equals(IS_CLOSED_PROPERTY)) { 
         boolean changed = ((Boolean) pce.getNewValue()).booleanValue(); 
         if (changed) { 
            int option = JOptionPane.showOptionDialog(this, "Close " + 
                                                       getTitle() + "?", 
                                                       "Close Confirmation", 
                                                       JOptionPane.YES_NO_OPTION, 
                                                       JOptionPane.QUESTION_MESSAGE, 
                                                       null, null, null); 
            if (option != JOptionPane.YES_OPTION) { 
               throw new PropertyVetoException("Cancelled",null); 
            } 
         } 
      } 
   }
} 

Disabling some of the elements in a JComboBox

We wrap a JComboBox element in our ConditionalItem object that includes a boolean variable isEnabled. Now, in order to change the default behavior of the JComboBox, we need to handle two things: first blur out the elements that are disabled using our own renderer and second ensure the disabled elements cannot be selected by adding a ActionListener that selects the old selected element in case a disabled item was selected.

Main.java:

import javax.swing.plaf.basic.*;
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 ConditionalItem[] { 
               new ConditionalItem("Item 1"),
               new ConditionalItem("Item 2", false),
               new ConditionalItem("Item 3", false),
               new ConditionalItem("Item 4")
            }
         );
 
      getContentPane().add(combobox);
      combobox.setRenderer(new ConditionalComboBoxRenderer());
      combobox.addActionListener(new ConditionalComboBoxListener(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);
   }
}
 
class ConditionalComboBoxRenderer extends BasicComboBoxRenderer implements ListCellRenderer
{
   public Component getListCellRendererComponent(JList list, 
           Object value, int index, boolean isSelected, boolean cellHasFocus) {
      if (isSelected) {
        setBackground(list.getSelectionBackground());
        setForeground(list.getSelectionForeground());
      } else {
        setBackground(list.getBackground());
        setForeground(list.getForeground());
      } 
 
      if (!((Conditionable) value).isEnabled()) {
        setBackground(list.getBackground());
        setForeground(UIManager.getColor("Label.disabledForeground"));
      }
 
      setFont(list.getFont());
      setText((value == null) ? "" : value.toString());
      return this;
   }  
}
 
class ConditionalComboBoxListener implements ActionListener {
   JComboBox combobox;
   Object oldItem;
    
   ConditionalComboBoxListener(JComboBox combobox) {
      this.combobox = combobox;
      combobox.setSelectedIndex(0);
      oldItem = combobox.getSelectedItem();
   }
    
   public void actionPerformed(ActionEvent e) {
      Object selectedItem = combobox.getSelectedItem();
      if (!((Conditionable) selectedItem).isEnabled()) {
         combobox.setSelectedItem(oldItem);
      } else {
         oldItem = selectedItem;
      }
   }
}
 
class ConditionalItem implements Conditionable {
   Object  object;
   boolean isEnabled;
    
   ConditionalItem(Object object, boolean isEnabled) {
      this.object = object;
      this.isEnabled = isEnabled;
   }
    
   ConditionalItem(Object object) {
     this(object, true);
   }
   
   public boolean isEnabled() {
      return isEnabled;
   }
    
   public void setEnabled(boolean isEnabled) {
      this.isEnabled = isEnabled;
   }
    
   public String toString() {
      return object.toString();
   }
}
 
interface Conditionable {
   public boolean isEnabled();
   public void setEnabled(boolean enabled);
   public String toString();
}

Disable a JList element

Create your custom CellRenderer that takes care of blurring out the disabled items. But beware, you are still able to select them, even though you don’t see a proof for this visually. Add a custom SelectionListener and unselect the disabled items that were clicked on. Here’s the code:

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 ConditionableItem[] { 
                                       new ConditionableItem("Item 1"),
                                       new ConditionableItem("Item 2", false),
                                       new ConditionableItem("Item 3", false),
                                       new ConditionableItem("Item 4")
                                   });

      list.setCellRenderer(new ConditionableCellRenderer());
      list.addListSelectionListener(new ConditionableListSelectionListener());
      getContentPane().add(new JScrollPane(list));    
 
      addWindowListener(new WindowAdapter() {
         public void windowClosing(WindowEvent event) {
            System.out.println("Selected items were:");
            Object sv[] = list.getSelectedValues();
            for (int i=0; i<sv.length; i++)
               System.out.println(sv[i]);
 
            System.exit(0);   
         }      
      });
 
      setSize(200, 300);
   }
   
   public static void main(String[] args) {
      (new Main()).show();
   }
}
 
class ConditionableCellRenderer extends DefaultListCellRenderer implements ListCellRenderer {
   public Component getListCellRendererComponent(
      JList list, Object value, int index, boolean isSelected, boolean cellHasFocus)    
   {
      setText((value == null) ? "" : value.toString());
      if (isSelected) {
         setBackground(list.getSelectionBackground());
         setForeground(list.getSelectionForeground());
      }
      else {
         setBackground(list.getBackground());
         setForeground(list.getForeground());
      }
 
      if (!((Conditionable) value).isEnabled()) {
         setBackground(list.getBackground());
         setForeground(UIManager.getColor("Label.disabledForeground"));
      }
 
      setEnabled(list.isEnabled());
      setFont(list.getFont());
 
      return this;
   }
}
 
class ConditionableListSelectionListener implements ListSelectionListener {
   public void valueChanged(ListSelectionEvent e) {
      JList list = (JList) e.getSource();
      ListModel lm = list.getModel();
      for (int i=e.getFirstIndex(); i<=e.getLastIndex(); i++) {
         if (list.getSelectionModel().isSelectedIndex(i)) {
            if (!((Conditionable) lm.getElementAt(i)).isEnabled()) {
               list.removeSelectionInterval(i, i);
            }
         }
      }
   }
}
 
class ConditionableItem implements Conditionable {
   Object  object;
   boolean isEnabled;
                            
   public ConditionableItem(Object object, boolean isEnabled) {
      this.object = object;
      this.isEnabled = isEnabled;
   }
                             
   ConditionableItem(Object object) {
      this(object, true);
   }
                           
   public boolean isEnabled() {
      return isEnabled;
   }
                            
   public void setEnabled(boolean isEnabled) {
      this.isEnabled = isEnabled;
   }
                            
   public String toString() {
      return object.toString();
   }
}
                         
interface Conditionable {
   public boolean isEnabled();
   public void setEnabled(boolean enabled);
   public String toString();
}

Displaying the description of a JMenuItem in the statusbar when moving over it

Add a ChangeListener. Here’s an example:

Main.java:

import javax.swing.event.*;
import java.awt.event.*;
import javax.swing.*;
import java.awt.*;
   
public class Main extends JFrame {
   public Main() {
      getContentPane().setLayout(new BorderLayout());
 
      JMenuBar menuBar = new JMenuBar();
      JMenu menu = new JMenu("Sex");
      JMenuItem menuItem1 = new JMenuItem("male");
      JMenuItem menuItem2 = new JMenuItem("female");
      JMenuItem menuItem3 = new JMenuItem("androgyne");
 
      // add the MenuItems to the Menu 
      menu.add(menuItem1);
      menu.add(menuItem2);
      menu.add(menuItem3);
 
      StatusBar statusBar = new StatusBar();
 
      new JMenuItemHelpText(menuItem1, "The weak sex", statusBar);
      new JMenuItemHelpText(menuItem2, "The strong sex", statusBar);
      new JMenuItemHelpText(menuItem3, "The average sex, I guess", statusBar);
 
      menuBar.add(menu);
 
      this.setJMenuBar(menuBar); 
      getContentPane().add(BorderLayout.SOUTH, statusBar);
 
      addWindowListener(new WindowAdapter() {
         public void windowClosing(WindowEvent event) {
            System.exit(0);   
         }      
      });
 
      setSize(400, 400);
   }
 
   public static void main(String[] args) {
      (new Main()).show();
   }
}
 
class JMenuItemHelpText implements ChangeListener
{
   JMenuItem menuItem;
   String helpText;
   StatusBar statusBar;
 
   JMenuItemHelpText(JMenuItem menuItem, String helpText, StatusBar statusBar) {
      this.menuItem = menuItem;
      this.helpText = helpText;
      this.statusBar = statusBar;
      menuItem.addChangeListener(this);
   } 
 
   public void stateChanged(ChangeEvent evt)
   {
      if (menuItem.isArmed())
         statusBar.setStatus(helpText);
      else
         statusBar.setStatus("");
   }
}
 
class StatusBar extends JPanel
{
   private JLabel statusLabel;
 
   public StatusBar() {
      setLayout(new BorderLayout(2, 2));
      statusLabel = new JLabel("Ready");
      statusLabel.setBorder(BorderFactory.createLoweredBevelBorder());
      statusLabel.setForeground(Color.black);
 
      add(BorderLayout.CENTER, statusLabel);
       
      JLabel dummyLabel = new JLabel("       ");
      dummyLabel.setBorder(BorderFactory.createLoweredBevelBorder());
 
      add(BorderLayout.EAST, dummyLabel);
   }
 
   public void setStatus(String status) {
      if (status.equals("")) 
         statusLabel.setText("Ready");
      else
         statusLabel.setText(status);
   }
 
   public String getStatus() {
      return statusLabel.getText();
   }
}

Detecting that the mouse enters my JTextField component

Implement a mouseListener and override the methods mouseEntered and mouseExited.
Main.java:

import java.awt.event.*;
import javax.swing.*;
import java.awt.*;
 
public class Main extends JFrame
{
   public Main() {
      getContentPane().setLayout(new FlowLayout());
      JTextField textfield = new JTextField(20);
      getContentPane().add(textfield);
      final JLabel label = new JLabel();
      getContentPane().add(label);
 
      textfield.addMouseListener(new MouseAdapter() {
         public void mouseEntered(MouseEvent me) {
            label.setText("Mouse is inside JTextField!");
         }
         public void mouseExited(MouseEvent me) {
            label.setText("");
         }
      });
 
      addWindowListener(new WindowAdapter() {
         public void windowClosing(WindowEvent we) {
            System.exit(0);
         }
      });
   }
 
   public static void main(String [] args) {
      Main main = new Main();
      main.setSize(300, 300);
      main.setVisible(true);
   } 
}