What Is a Socket?

A socket is one end-point of a two-way communication link between two programs running on the network. Socket classes are used to represent the connection between a client program and a server program. The java.net package provides two classes--Socket and ServerSocket--that implement the client side of the connection and the server side of the connection, respectively.

Dynamic Tree Node

// Add child and parent node dynamically in to existing root tree node.
There are two file DynamicTree.java and DynamicTreeDemo.java.

** download or copy from here and paste in your workspace and run DynamicTreeDemo.java as bean.


DynamicTree.java

//package components;

import java.awt.GridLayout;
import java.awt.Toolkit;

import javax.swing.ImageIcon;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTree;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.DefaultTreeModel;
import javax.swing.tree.MutableTreeNode;
import javax.swing.tree.TreePath;
import javax.swing.tree.TreeSelectionModel;
import javax.swing.event.TreeModelEvent;
import javax.swing.event.TreeModelListener;
//Dynamically add parent and child node in a existing tree
public class DynamicTree extends JPanel {
    protected DefaultMutableTreeNode rootNode;
    protected DefaultTreeModel treeModel;
    protected JTree tree;
    private Toolkit toolkit = Toolkit.getDefaultToolkit();

    public DynamicTree() {
        super(new GridLayout(1,0));
       
        rootNode = new DefaultMutableTreeNode("Root Node");
        treeModel = new DefaultTreeModel(rootNode);
    treeModel.addTreeModelListener(new MyTreeModelListener());
        tree = new JTree(treeModel);
        tree.setEditable(true);
        tree.getSelectionModel().setSelectionMode
                (TreeSelectionModel.SINGLE_TREE_SELECTION);
        tree.setShowsRootHandles(true);

        JScrollPane scrollPane = new JScrollPane(tree);
        add(scrollPane);
    }

    /** Remove all nodes except the root node. */
    public void clear() {
        rootNode.removeAllChildren();
        treeModel.reload();
    }

    /** Remove the currently selected node. */
    public void removeCurrentNode() {
        TreePath currentSelection = tree.getSelectionPath();
        if (currentSelection != null) {
            DefaultMutableTreeNode currentNode = (DefaultMutableTreeNode)
                         (currentSelection.getLastPathComponent());
            MutableTreeNode parent = (MutableTreeNode)(currentNode.getParent());
            if (parent != null) {
                treeModel.removeNodeFromParent(currentNode);
                return;
            }
        }

        // Either there was no selection, or the root was selected.
        toolkit.beep();
    }

    /** Add child to the currently selected node. */
    public DefaultMutableTreeNode addObject(Object child) {
        DefaultMutableTreeNode parentNode = null;
        TreePath parentPath = tree.getSelectionPath();

        if (parentPath == null) {
            parentNode = rootNode;
        } else {
            parentNode = (DefaultMutableTreeNode)
                         (parentPath.getLastPathComponent());
        }

        return addObject(parentNode, child, true);
    }

    public DefaultMutableTreeNode addObject(DefaultMutableTreeNode parent,
                                            Object child) {
        return addObject(parent, child, false);
    }

    public DefaultMutableTreeNode addObject(DefaultMutableTreeNode parent,
                                            Object child,
                                            boolean shouldBeVisible) {
        DefaultMutableTreeNode childNode =
                new DefaultMutableTreeNode(child);

        if (parent == null) {
            parent = rootNode;
        }
   
    //It is key to invoke this on the TreeModel, and NOT DefaultMutableTreeNode
        treeModel.insertNodeInto(childNode, parent,
                                 parent.getChildCount());

        //Make sure the user can see the lovely new node.
        if (shouldBeVisible) {
            tree.scrollPathToVisible(new TreePath(childNode.getPath()));
        }
        return childNode;
    }

    class MyTreeModelListener implements TreeModelListener {
        public void treeNodesChanged(TreeModelEvent e) {
            DefaultMutableTreeNode node;
            node = (DefaultMutableTreeNode)(e.getTreePath().getLastPathComponent());

            /*
             * If the event lists children, then the changed
             * node is the child of the node we've already
             * gotten.  Otherwise, the changed node and the
             * specified node are the same.
             */

                int index = e.getChildIndices()[0];
                node = (DefaultMutableTreeNode)(node.getChildAt(index));

            System.out.println("The user has finished editing the node.");
            System.out.println("New value: " + node.getUserObject());
        }
        public void treeNodesInserted(TreeModelEvent e) {
        }
        public void treeNodesRemoved(TreeModelEvent e) {
        }
        public void treeStructureChanged(TreeModelEvent e) {
        }
    }
}

 DynamicTreeDemo.java


import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.tree.DefaultMutableTreeNode;

public class DynamicTreeDemo extends JPanel
                             implements ActionListener {
    private int newNodeSuffix = 1;
    private static String ADD_COMMAND = "add";
    private static String REMOVE_COMMAND = "remove";
    private static String CLEAR_COMMAND = "clear";
   
    private DynamicTree treePanel;

    public DynamicTreeDemo() {
        super(new BorderLayout());
       
        //Create the components.
        treePanel = new DynamicTree();
        populateTree(treePanel);

        JButton addButton = new JButton("Add");
        addButton.setActionCommand(ADD_COMMAND);
        addButton.addActionListener(this);
       
        JButton removeButton = new JButton("Remove");
        removeButton.setActionCommand(REMOVE_COMMAND);
        removeButton.addActionListener(this);
       
        JButton clearButton = new JButton("Clear");
        clearButton.setActionCommand(CLEAR_COMMAND);
        clearButton.addActionListener(this);

        //Lay everything out.
        treePanel.setPreferredSize(new Dimension(300, 150));
        add(treePanel, BorderLayout.CENTER);

        JPanel panel = new JPanel(new GridLayout(0,3));
        panel.add(addButton);
        panel.add(removeButton);
        panel.add(clearButton);
    add(panel, BorderLayout.SOUTH);
    }

    public void populateTree(DynamicTree treePanel) {
        String p1Name = new String("Parent 1");
        String p2Name = new String("Parent 2");
        String c1Name = new String("Child 1");
        String c2Name = new String("Child 2");

        DefaultMutableTreeNode p1, p2;

        p1 = treePanel.addObject(null, p1Name);
        p2 = treePanel.addObject(null, p2Name);

        treePanel.addObject(p1, c1Name);
        treePanel.addObject(p1, c2Name);

        treePanel.addObject(p2, c1Name);
        treePanel.addObject(p2, c2Name);
    }
   
    public void actionPerformed(ActionEvent e) {
        String command = e.getActionCommand();
       
        if (ADD_COMMAND.equals(command)) {
            //Add button clicked
            treePanel.addObject("New Node " + newNodeSuffix++);
        } else if (REMOVE_COMMAND.equals(command)) {
            //Remove button clicked
            treePanel.removeCurrentNode();
        } else if (CLEAR_COMMAND.equals(command)) {
            //Clear button clicked.
            treePanel.clear();
        }
    }

    /**
     * Create the GUI and show it.  For thread safety,
     * this method should be invoked from the
     * event-dispatching thread.
     */
    private static void createAndShowGUI() {
        //Create and set up the window.
        JFrame frame = new JFrame("DynamicTreeDemo");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        //Create and set up the content pane.
        DynamicTreeDemo newContentPane = new DynamicTreeDemo();
        //newContentPane.setOpaque(true); //content panes must be opaque
        frame.setContentPane(newContentPane);

        //Display the window.
        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        //Schedule a job for the event-dispatching thread:
        //creating and showing this application's GUI.
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI();
            }
        });
    }
}

 ** Run DynamicTreeDemo and see what you want.