FileDocCategorySizeDatePackage
DynamicTreeNode.javaAPI DocSun JDK 1.4.2 Example6837Thu May 12 00:35:28 BST 2005None

DynamicTreeNode

public class DynamicTreeNode extends DefaultMutableTreeNode
DynamicTreeNode illustrates one of the possible ways in which dynamic loading can be used in tree. The basic premise behind this is that getChildCount() will be messaged from JTreeModel before any children are asked for. So, the first time getChildCount() is issued the children are loaded.

It should be noted that isLeaf will also be messaged from the model. The default behavior of TreeNode is to message getChildCount to determine this. As such, isLeaf is subclassed to always return false.

There are others ways this could be accomplished as well. Instead of subclassing TreeNode you could subclass JTreeModel and do the same thing in getChildCount(). Or, if you aren't using TreeNode you could write your own TreeModel implementation. Another solution would be to listen for TreeNodeExpansion events and the first time a node has been expanded post the appropriate insertion events. I would not recommend this approach though, the other two are much simpler and cleaner (and are faster from the perspective of how tree deals with it). NOTE: getAllowsChildren() can be messaged before getChildCount(). For this example the nodes always allow children, so it isn't a problem, but if you do support true leaf nodes you may want to check for loading in getAllowsChildren too.

version
1.10 01/23/03
author
Scott Violet

Fields Summary
protected static float
nameCount
Number of names.
protected static String[]
names
Names to use for children.
protected static Font[]
fonts
Potential fonts used to draw with.
protected static Random
nameGen
Used to generate the names.
protected static final int
DefaultChildrenCount
Number of children to create for each node.
protected boolean
hasLoaded
Have the children of this node been loaded yet?
Constructors Summary
public DynamicTreeNode(Object o)
Constructs a new DynamicTreeNode instance with o as the user object.

	super(o);
Methods Summary
public intgetChildCount()
If hasLoaded is false, meaning the children have not yet been loaded, loadChildren is messaged and super is messaged for the return value.

	if(!hasLoaded) {
	    loadChildren();
	}
	return super.getChildCount();
public booleanisLeaf()

	return false;
protected voidloadChildren()
Messaged the first time getChildCount is messaged. Creates children with random names from names.

	DynamicTreeNode             newNode;
	Font                        font;
	int                         randomIndex;
	SampleData                  data;

	for(int counter = 0; counter < DynamicTreeNode.DefaultChildrenCount;
	    counter++) {
	    randomIndex = (int)(nameGen.nextFloat() * nameCount);
	    if(fonts != null)
		font = fonts[randomIndex];
	    else
		font = null;
	    if(counter % 2 == 0)
		data = new SampleData(font, Color.red, names[randomIndex]);
	    else
		data = new SampleData(font, Color.blue, names[randomIndex]);
	    newNode = new DynamicTreeNode(data);
	    /* Don't use add() here, add calls insert(newNode, getChildCount())
	       so if you want to use add, just be sure to set hasLoaded = true
	       first. */
	    insert(newNode, counter);
	}
	/* This node has now been loaded, mark it so. */
	hasLoaded = true;