Java Video Tutorial 27
In this part of the Java Video Tutorial, I introduce the last Swing component called the JTree. I won’t just be introducing the JTree however. I will also be reviewing much of what you have learned.
It is my belief that if you see tools being used in many different ways, that you will just remember them. I will review dimensions, frames, panels, buttons, scroll bars, listeners and so much more.
Use the code after the video to better learn how to use Java Swing.
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Code From the Video
import javax.swing.*;
import java.awt.event.*;
import java.awt.Dimension;
// Enumerations are used to store related items together
import java.util.Enumeration;
import javax.swing.tree.*;
public class Lesson27 extends JFrame{
JButton button1;
String outputString = "";
// A Tree contains nodes that can contain other nodes
JTree theTree;
// If a node holds other nodes it is called a parent node
// The nodes inside of a parent node are children nodes
// Nodes on the same level are called siblings
DefaultMutableTreeNode documents, work, games, emails;
DefaultMutableTreeNode fileSystem = new DefaultMutableTreeNode("C Drive");
public static void main(String[] args){
new Lesson27();
}
public Lesson27(){
this.setSize(400,400);
this.setLocationRelativeTo(null);
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
this.setTitle("My Sixth Frame");
JPanel thePanel = new JPanel();
// Create a button
button1 = new JButton("Get Answer");
ListenForButton lForButton = new ListenForButton();
button1.addActionListener(lForButton);
thePanel.add(button1);
// Create the JTree by passing it the top tree node
theTree = new JTree(fileSystem);
// Makes sure only one item can be selected at a time
// By default you can make multiple selections
theTree.getSelectionModel().setSelectionMode(TreeSelectionModel.SINGLE_TREE_SELECTION);
// Only show 8 rows of the tree at a time
theTree.setVisibleRowCount(8);
// Add the items to the tree documents, work, games
// We first add the documents parent node
documents = addAFile("Docs", fileSystem);
// Now we add children nodes to the documents parent node
addAFile("Taxes.exl", documents);
emails = addAFile("Emails", documents);
addAFile("Story.txt", documents);
addAFile("Schedule.txt", documents);
// Add a child node to the email node
addAFile("CallBob.txt", emails);
// Create the work node and its children
work = addAFile("Work Applications", fileSystem);
addAFile("Spreadsheet.exe", work);
addAFile("Wordprocessor.exe", work);
addAFile("Presentation.exe", work);
// Create the games node and its children
games = addAFile("Games", fileSystem);
addAFile("SpaceInvaders.exe", games);
addAFile("PacMan.exe", games);
// Put the tree in a scroll component
JScrollPane scrollBox = new JScrollPane(theTree);
// Set the size for the JScrollPane so that everything fits
Dimension d = scrollBox.getPreferredSize();
d.width = 200;
scrollBox.setPreferredSize(d);
thePanel.add(scrollBox);
this.add(thePanel);
this.setVisible(true);
}
private DefaultMutableTreeNode addAFile(String fileName, DefaultMutableTreeNode parentFolder){
// Creates a new node for the tree
DefaultMutableTreeNode newFile = new DefaultMutableTreeNode(fileName);
// Add attaches a name to the node
parentFolder.add(newFile);
// return the new node
return newFile;
}
private class ListenForButton implements ActionListener{
public void actionPerformed(ActionEvent e){
if(e.getSource() == button1){
// How to get the selected node
// Returns the last selected node in the tree
Object treeObject = theTree.getLastSelectedPathComponent();
// Cast the Object into a DefaultMutableTreeNode
DefaultMutableTreeNode theFile = (DefaultMutableTreeNode) treeObject;
// Returns the object stored in this node and casts it to a string
String treeNode = (String) theFile.getUserObject();
outputString = "The Selected Node: " + treeNode + "\n";
// Get the number of children this node has
outputString += "Number of Children: " + theFile.getChildCount() + "\n";
// Get the number of siblings
outputString += "Number of Siblings: " + theFile.getSiblingCount() + "\n";
// Get the parent of this node
outputString += "The parent: " + theFile.getParent() + "\n";
// Get the next node
outputString += "Next Node: " + theFile.getNextNode() + "\n";
// Get the previous node
outputString += "Next Node: " + theFile.getPreviousNode() + "\n";
// Get the children for the node
outputString += "\nChildren of Node\n";
// children() returns an enumeration that contains all the children
// This for loop will continue to run as long as there are more elements
// nextElement() returns the next element in the list
for (Enumeration enumValue = theFile.children(); enumValue.hasMoreElements(); ) {
outputString += enumValue.nextElement() + "\n";
}
// Get the path from the root
outputString += "\nPath From Root\n";
// getPath returns an array of TreeNodes
TreeNode[] pathNodes = theFile.getPath();
// Cycle through the TreeNodes
for(TreeNode indivNodes: pathNodes){
outputString += indivNodes + "\n";
}
JOptionPane.showMessageDialog(Lesson27.this, outputString, "Information", JOptionPane.INFORMATION_MESSAGE);
outputString = "";
}
}
}
}
hello darek, can you please tell me how to generate reports, i mean i have to generate a report in swing, i mean i have fetch some data on panel and have to print that, how can i do this??
Thank You
I’m going to cover JTable very soon. I’m working on it now
no actually i want to ask is that, i have a page(hard copy), which has fix header and footer(in all the pages, (hard copy)), and now i want to print report in between header and footer, the report is simple, i fetched some data from database(ie. name, age and all).
how do i print that on paper??
You’ll find that capability in these two libraries java.awt.print and javax.print
okay..
thank you very much..
how do i place the tree to the right?
I’m sorry, but I don’t know what you mean by placing it to the right?
I Think he ment align to right.
so the internal file will open down to it indented to the left.
and you videos are great!
hi derek i have a question,
whenever u are calling addAFile(“Taxes.exl”, documents);
here i know what happens taxes.exl gets added to documents.
but i have a confusion, when we call the method like this
addAFile(“Taxes.exl”, documents);
the method returns a node and in this case its taxes.exl but when the method returns the node we are not holding it anywhere when control returns from addaFile method and even compiler does not show the error. can u explain whaz is going on here plz
Regards,
Aamir
Banglore,India.