Using SWT JFace TreeViewer

Create a ContentProvider for the TreeViewer: implement the methods in ITreeContentProvider. The following example shows you how to do this. The business objects are Category and Link. (For an extension of this code, check the Q&A How do I use a Sash?

Category.java:

import java.util.*;
 
public class Category {
   private String name;
   private Category parent;
   private ArrayList categories = new ArrayList();
   private ArrayList links = new ArrayList();
   
   public Category(String name, Category parent) {
      this.name = name;
      this.parent = parent;
   }
   
   public void addSubCategory(Category category) {
      categories.add(category);
   }
   
   public void addLink(Link link) {
      links.add(link);
   }
   
   public ArrayList getSubCategories() {
      return categories;
   }
   
   public ArrayList getLinks() {
      return links;
   }
   
   public boolean hasSubCategories() {
      return categories.size() > 0;
   }
   
   public boolean hasLinks() {
      return links.size() > 0;
   }
   
   public String getName() {
      return name;
   }
   
   public Category getParent() {
      return parent;
   }
   
   public String toString() {
      return name;
   }
}

Link.java:

public class Link {
   private String url;
   
   public Link(String url) {
      this.url = url;
   }
   
   public String getUrl() {
      return url;
   }
   
   public String toString() {
      return url;
   }
}

CategoryTreeContentProvider.java:

import org.eclipse.jface.viewers.*;
import java.util.*;
 
public class CategoryTreeContentProvider implements ITreeContentProvider 
{
   public Object[] getChildren(Object element) {
      Category category = (Category) element;
      System.out.println(category.getName());
      
      ArrayList children = new ArrayList();
      children.addAll(category.getSubCategories());
      children.addAll(category.getLinks());
            
      if (children.size() == 0) {
         return new Object[0];
      }
      
      return children.toArray();
   }
   
   public Object[] getElements(Object element) {
      return getChildren(element);
   }
   
   public boolean hasChildren(Object element) {
      if (element instanceof Category) {
         Category category = (Category) element;
      
         return category.hasSubCategories() || category.hasLinks();
      }
      
      return false;
   }
   
   public Object getParent(Object element) {
      if (element instanceof Category) {
         return ((Category) element).getParent();
      }
      
      return null;
   }
   
   public void dispose() {
      
   }
   
   public void inputChanged(Viewer viewer, Object oldInput, Object newInput) {
      
   }
}

Main.java:

import org.eclipse.jface.viewers.*;
import org.eclipse.jface.window.*;
import org.eclipse.swt.widgets.*;
 
public class Main extends ApplicationWindow 
{
   private Category rootCategory;
   
   public Main() {
      super(null);
      
      // statically create categories
      rootCategory = new Category("Java", null);
      Category j2seCategory = new Category("J2SE", rootCategory);
      Link link = new Link("http://java.sun.com/j2se/");
      j2seCategory.addLink(link);
      Category j2eeCategory = new Category("J2EE", rootCategory);
      link = new Link("http://java.sun.com/j2se/");
      j2eeCategory.addLink(link);
      Category j2meCategory = new Category("J2ME", rootCategory);
      link = new Link("http://java.sun.com/j2se/");
      j2meCategory.addLink(link);
      
      rootCategory.addSubCategory(j2seCategory);
      rootCategory.addSubCategory(j2eeCategory);
      rootCategory.addSubCategory(j2meCategory);
   }
   
   protected Control createContents(Composite parent) {
      TreeViewer treeViewer = new TreeViewer(parent);
      treeViewer.setContentProvider(new CategoryTreeContentProvider());
      treeViewer.setInput(rootCategory);
      
      return treeViewer.getTree();
   }
   
   public static void main(String []args) {
      Main main = new Main();
      main.setBlockOnOpen(true);
      main.open();
      
      Display.getCurrent().dispose();
   }
}

The contents that is displayed in the tree using the toString() method in Category and Link. This is not a clean separation of model and view. Instead, you can use a LabelProvider, a helper class with a callback method getText(Element).

CategoryTreeLabelProvider.java:

import org.eclipse.jface.viewers.*;
 
public class CategoryTreeLabelProvider extends LabelProvider
{
   public String getText(Object element) {
      if (element instanceof Category) {
         return ((Category) element).getName();
      }
      else if (element instanceof Link) {
         return ((Link) element).getUrl();
      }
      
      return "" + element;
   }
}

Modify your Main class:

   treeViewer.setLabelProvider(new CategoryTreeLabelProvider());