Saturday, 30 December 2017

Simple program which demonstrates Swing/AWT Grid layout

Simple program which demonstrates Swing/AWT Grid layout:

This post is intended to the beginners of swing/awt.

This below program creates a JFrame with 2 labels, 2 textfields and 2 buttons.

import java.awt.GridLayout;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPasswordField;
import javax.swing.JTextField;

 * @author Nagasharath Kopalle
 * Simple program to demontrate Gridlayout
public class GridLayoutDemo extends JFrame {

private JLabel labelName = null;

private JTextField textFieldName = null;

private JLabel labelPassword = null;

private JPasswordField passwordFieldPassword = null;

private JButton buttonSubmit = null;

private JButton buttonCancel = null;

public GridLayoutDemo() {

* instantiates components and adds properties.
void initComponents() {

this.setTitle("Grid Layout Demo");
this.setSize(300, 200);
GridLayout layout = new GridLayout(3, 2);
labelName = new JLabel("User Name: ");
textFieldName = new JTextField();

labelPassword = new JLabel("Password: ");
passwordFieldPassword = new JPasswordField();

buttonSubmit = new JButton("Submit");
buttonCancel = new JButton("Cancel");




public static void main(String[] args) {

GridLayoutDemo demo = new GridLayoutDemo();


Sunday, 29 October 2017

Eclipse Java Editor Shortcuts

Eclipse Oxygen Java editor Shortcuts helps in editing source code more comfortably. Frequently used default shortcuts are listed below. 

Delete Line
Copy Line
CTRL + ALT + Down Arrow
Add method level, class level, member level Comments
Format Java Source code
Make line commented
CTRL + /
Make multiple lines [block] commented  
Search selected similar word within the source document
Select line from beginning to end
SHIFT + End key
Select line from end to beginning
SHIFT + Home key
Select Word by word in same line
CTRL + SHIFT + Right Arrow
Move line above
ALT + Up Arrow
Move line below
ALT + Down Arrow

Shortcuts can be customized and new shortcuts can be created through Keys Page in Preferences wizard.

  1.  Window menu > Go To Preferences 
  2.  Type Keys as the "filter text"
  3.  Please find the image below for reference.

Add new Shortcut for cut whole line command.

  1.  In Keys page type filter text -- Cut line
  2.  Type your convenient key. In my case I added SHIFT + X
  3.  Finally, Click Apply and Click Apply and Close.
  4.  That's it. Now Test your new Shortcut. 

Happy Coding :)

Saturday, 21 October 2017

Launch Swing GUI always in a dedicated Thread

1. Since Swing is not thread safe, it is not at all a good practice to launch a UI Container like JFrame, JDialog etc in main Thread.
2. Doing so leads to incorrect behavior of java GUI.
3. To avoid this, Swing toolkit has predefined API as part of JFC.
4.    a. SwingUtilities.invokeAndWait(Runnable r);
       b. SwingUtilities.invokeLater(Runnable r);

5. Which part of the code must be in UI Thread?
        a. setVisible(true);
        b. show(); [deprecated]
 and c. pack();

6. Call to these methods mentioned in 5(a), 5(b), and 5(c) must happen in one of the methods mentioned in point 4(a) and point 4(b). That's enough. :)
         Example :
         public static void main(String[] args){
         JFrame frame = new JFrame();
         frame.setSize(100, 200);
         SwingUtilities.invokeAndWait(new Runnable(){
             public void run(){

  7. Difference between invokeAndWait() and invokeLater():
          a. invokeLater() is non blocking and asynchronous, where as invokeAndWait() is blocking and synchronous.
          b. Since invokeLater() is asynchronous, It is more flexible.

Friday, 6 October 2017

File Manager/File Explorer with Swing JTree Component

This post is intended to beginners of java swing toolkit programmers.
It is a simple java program which demonstrates the swing based File explorer GUI.

import java.awt.GridLayout;
import java.lang.reflect.InvocationTargetException;
import java.util.Arrays;
import java.util.List;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTree;
import javax.swing.SwingUtilities;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.event.TreeModelListener;
import javax.swing.tree.TreeModel;
import javax.swing.tree.TreePath;

 * @author NagasharathK
public class FileExplorer extends JFrame {

private JTree fileManagerTree = null;

public FileExplorer() {

* Initializes components
private void initComponents() {
this.getContentPane().add(new JScrollPane(createFileManagerTree()));
this.setSize(500, 500);
this.setTitle("File Manager..");

* @return JPanel object which contains other comp...
private JPanel createFileManagerTree() {
JPanel panel = new JPanel();
panel.setLayout(new GridLayout());

fileManagerTree = new JTree();
fileManagerTree.setModel(new FilesContentProvider("C:\\"));
return panel;

class FilesContentProvider implements TreeModel {

private File node;

public FilesContentProvider(String path) {
node = new File(path);


public void addTreeModelListener(TreeModelListener l) {


public Object getChild(Object parent, int index) {
if (parent == null)
return null;
return ((File) parent).listFiles()[index];

public int getChildCount(Object parent) {
if (parent == null)
return 0;
return (((File) parent).listFiles() != null) ? ((File) parent).listFiles().length : 0;

public int getIndexOfChild(Object parent, Object child) {
List<File> list = Arrays.asList(((File) parent).listFiles());
return list.indexOf(child);

public Object getRoot() {
return node;

public boolean isLeaf(Object node) {
return ((File) node).isFile();

public void removeTreeModelListener(TreeModelListener l) {


public void valueForPathChanged(TreePath path, Object newValue) {



* @param args
* @throws InvocationTargetException
* @throws InterruptedException
* @throws UnsupportedLookAndFeelException
* @throws IllegalAccessException
* @throws InstantiationException
* @throws ClassNotFoundException
public static void main(String[] args) throws InvocationTargetException, InterruptedException,
ClassNotFoundException, InstantiationException, IllegalAccessException, UnsupportedLookAndFeelException {
FileExplorer explorerUI = new FileExplorer();
SwingUtilities.invokeAndWait(new Runnable() {
public void run() {

The above program has one inner class [FilesContentProvider] which serves as a model to the JTree.

The UI has 4 Components: JFrame, JScrollPane, JPanel and JTree.

To Do:

  1. Add Context menu to node based upon the file type
  2. Add Cell renderer to give proper names to the Nodes
  3. Option to Expand whole tree or selected node etc..