Home > Articles > Programming > Java

This chapter is from the book

This chapter is from the book

The DefaultMutableTreeNode Class

The first thing we're going to do with this class is to show you how to use it to build a simple tree from scratch. DefaultMutableTreeNode has three constructors:

public DefaultMutableTreeNode() 
public DefaultMutableTreeNode(Object userObject) 
public DefaultMutableTreeNode(Object userObject, 
                   boolean allowsChildren) 

The first constructor creates a node with no associated user object; you can associate one with the node later using the setUserObject method. The other two connect the node to the user object that you supply. The second constructor creates a node to which you can attach children, while the third can be used to specify that child nodes cannot be attached by supplying the third argument as false.

Using DefaultMutableTreeNode, you can create nodes for the root and for all of the data you want to represent in the tree, but how do you link them together? You could use the insert method that we saw above, but it is simpler to use the DefaultMutableTreeNode add method:

public void add(MutableTreeNode child); 

This method adds the given node as a child of the node against which it is invoked and at the end of the parent's list of children. By using this method, you avoid having to keep track of how many children the parent has. This method, together with the constructors, gives us all you need to create a workable tree. To begin to create a tree, you need a root node:

DefaultMutableTreeNode rootNode 
                = new DefaultMutableTreeNode(); 

Below the root node, two more nodes are going to be added, one to hold details of the Apollo lunar flights, the other with information on the manned Skylab missions. These two nodes will be given meaningful text labels:

DefaultMutableTreeNode apolloNode =
                  new DefaultMutableTreeNode("Apollo"); 
DefaultMutableTreeNode skylabNode =
                  new DefaultMutableTreeNode("Skylab"); 

The nodes are then added directly beneath the root node:

rootNode.add(apolloNode); 
rootNode.add(skylabNode); 

Under each of these nodes, a further node will be added for each mission and beneath each of these a leaf node for each crew member. There's an implementation of this in the example programs that you can run using the command:

java JFCBook.Chapter10.TreeExample1 

The result of running this example is shown in Figure 10–8.

Figure 10–8 A tree built using DefaultMutableTreeNodes.

This program shows a root folder with no associated label and nodes labeled Apollo and Skylab. Clicking on the expansion icons of either of these opens it to show the numbered missions, and clicking on any of these shows the crew for that flight. Let's look at an extract from the source of this example:

import javax.swing.*;
import javax.swing.tree.*; 

public class TreeExample1 extends JTree {
  public TreeExample1() {
    DefaultMutableTreeNode rootNode =
                 new DefaultMutableTreeNode();
    DefaultMutableTreeNode apolloNode =
              new DefaultMutableTreeNode("Apollo");
    rootNode.add(apolloNode); 

    DefaultMutableTreeNode skylabNode =
              new DefaultMutableTreeNode("Skylab");
    rootNode.add(skylabNode); 

    // CODE OMITTED 

    this.setModel(new DefaultTreeModel(rootNode)); 
  } 
  public static void main(String[] args) { 
    JFrame f = new JFrame("Tree Example 1"); 

    TreeExample1 t = new TreeExample1(); 
    t.putClientProperty("JTree.lineStyle", "Angled");
    t.expandRow(0); 

    f.getContentPane().add(new JScrollPane(t)); 
    f.setSize(300, 300);
    f.setVisible(true);
  } 
} 

This class is defined as an extension of JTree, which allows the creation of its data to be encapsulated within it. The root node and all of the child nodes are created and a tree structure is built from the nodes as described earlier. The JTree needs a data model in order to display anything, so the last step of the constructor is to install a model that contains the structure that has just been created:

this.setModel(new DefaultTreeModel(rootNode)); 

This creates a new DefaultTreeModel and initializes it with our root node, then uses the JTree setModel method to associate the data model with the tree. Since our class is derived from JTree, its default constructor will have been invoked at the start of our constructor. As noted earlier, this creates a tree with a model containing dummy data. When setModel is called at the end of the constructor, this data is overwritten with the real data.

Another way to create a JTree is to directly pass it the root node. If you use this method, it creates a DefaultTreeModel of its own and wraps it around the node that you pass to its constructor. Here's a short example of that:

DefaultMutableTreeNode rootNode = 
                  new DefaultMutableTreeNode(); 
DefaultMutableTreeNode apolloNode = 
                  new DefaultMutableTreeNode("Apollo"); 
DefaultMutableTreeNode skylabNode = 
                  new DefaultMutableTreeNode("Skylab"); 
rootNode.add(apolloNode); 
rootnode.add(skylabNode); 
JTree t = new JTree(rootNode); 

If you look at the main method in the code extract shown above, you'll notice the following line after the tree was created:

t.expandRow(0); 

This line uses the expandRow method to ensure that row 0 of the tree is expanded to display the children that the node on that row contains. In fact, this line is redundant in this example because the root node is expanded by default. You can force a node to be shown in an unexpanded state by calling the collapseRow method, which also requires the index of the row within the tree. We'll say more about the methods that can be used to expand and collapse parts of the tree later in this chapter.

Apart from when you create it, the JTree control doesn't deal with nodes directly. Instead, you can address items in the tree and obtain information about them using either their TreePath or their row number. Let's look at the row number first. The row number refers to the number of the row on the screen at which the node in question appears. There is only one node ever on any row, so specifying the row identifies a node without any ambiguity. Furthermore, provided it's actually displayed, row 0 is always occupied by the root node. The problem with using row numbers is that the row numbers for all of the nodes apart from the root node change as nodes are opened or closed. When you start TreeExample1, the root node is on row 0, the "Apollo" node on row 1, and the "Skylab" node occupies row 2. However, if you click on the expansion icon for "Apollo," the "Skylab" node moves downward and, in this case, becomes row number 9, because the "Apollo" node opens to show seven child nodes, which will occupy rows 2 through 8. Because keeping track of row numbers is not very convenient, it is more usual to address the content of a tree using TreePath objects.

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020