June 29, 2012

Java Varargs - Unlimited parameters to a Java method

When you cannot decide the number of parameters you need for a method, varargs becomes the solution. Earlier, if we couldn't determine such, we had to use a collection as a parameter to help with this scenario. But varargs simplifies this.

Varargs does use an array underneath, but using varargs syntax hides the process.

public static String format(String pattern,
                                Object... arguments);

Example :

If you need to write a file name extension filter for a number of extensions, you can use this method of defining the method.

public FileNameExtensionFilter(String description, String... extensions) {

Read more on varargs at :

JFileChooser - Useful Tips

Set Starting Directory
JFileChooser fileSaver = new JFileChooser();
String cpath = "C:/MWork/Test1/script/";
File f1 = new File(cpath);

File Filter
FileNameExtensionFilter filter = new FileNameExtensionFilter("eXtensible Markup Language file (*.xml) ", "xml");
fileSaver .setFileFilter(filter);

Default File Save Name
jFileChooser.setSelectedFile(new File("untitled.xml"));

June 22, 2012

Get Frame of a Component

In order to find the frame that contains a component, it is necessary to walk up the component's parents until the frame is encountered. SwingUtilities.getRoot() is a convenience method that finds the frame.

This example implements an action that finds and hides the frame of the component that triggered the action. See also Creating a JButton Component.

// Create an action
Action action = new AbstractAction("Action Label") {
    // This method is called when the action is triggered
    public void actionPerformed(ActionEvent evt) {
        Component c = (Component)evt.getSource();

        // Get the frame
        Component frame = SwingUtilities.getRoot(c);

        // Hide the frame


June 21, 2012

XML Editor for Eclipse

Make sure you go to Open With -> XML Editor to make XML Editor the default for that XML

June 19, 2012

Focus to newly added JComponent in Frame

int h = (int) pnlPrerequisites.getBounds().getHeight();
Component frame = SwingUtilities.getRoot(pnlPrerequisites);
System.out.println(h + "=" + frame.getHeight());
if (h > frame.getHeight()) {
    // scrollPnlPre.getViewport().setView(p);

Problem : this removes the scroll

June 18, 2012

Get the string that matches the regex

If you want to get the string that matches the regex pattern you have defined, you might have noticed there isn't any direct method. As a solution a simple code as below can be used.

I wanted to read the number within the brackets in str.
(Note: The numbers always appear within brackets)
String str = "CLor (23)";
String search = "\\(\\d*\\)";
Pattern pattern = Pattern.compile(search);
Matcher matcher = pattern.matcher(str);
boolean matchFound = matcher.find();
if (matchFound) {
   int start = matcher.start();
   int end = matcher.end();
   String num = str.substring(start + 1, end - 1);

Above, in substring method I used
(start + 1, end -1)
because I needed to omit the brackets. If the whole string that matches the regex was needed method needs to have parameters