How to Load Children Lazily

Lazy loading is a characteristic of an application when the actual loading and instantiation of a class is delayed until the point just before the instance is actually used.

Do we gain anything by loading them lazily? Yes, this would definitely add to the performance of an application. By lazily loading, you can dedicate the memory resources to load and instantiate an object only when it is actually used. You can also speed up the initial loading time of an application.

One of the ways you can lazily load children of a Tree is by utilizing the TreeWillExpandListener interface. For example, you can declare and load root, grandparent and parent of a Tree along with the application as shown in the following code:

Let us declare the root, grandparent and parent as shown below:

class DemoArea extends JScrollPane

implements TreeWillExpandListener {

.......

.......

private TreeNode createNodes() {

DefaultMutableTreeNode root;

DefaultMutableTreeNode grandparent;

DefaultMutableTreeNode parent;

root = new DefaultMutableTreeNode("San Francisco");

grandparent = new DefaultMutableTreeNode("Potrero Hill");

root.add(grandparent);

parent = new DefaultMutableTreeNode("Restaurants");

grandparent.add(parent);

dummyParent = parent;

return root;

}

You can load above declared nodes to the tree as shown in the following code:

TreeNode rootNode = createNodes();

tree = new JTree(rootNode);

tree.addTreeExpansionListener(this);

tree.addTreeWillExpandListener(this);

.......

.......

setViewportView(tree);

Now, you can load children lazily to the application whenever the parent node Restaurants is visible in the application. To do this, let us declare two children in a separate method and call that method as shown in the following code:

private void LoadLazyChildren(){

DefaultMutableTreeNode child;

child = new DefaultMutableTreeNode("Thai Barbeque");

dummyParent.add(child);

child = new DefaultMutableTreeNode("Goat Hill Pizza");

dummyParent.add(child);

textArea.append(" Thai Barbeque and Goat Hill Pizza are loaded lazily");

}

.......

.......

public void treeWillExpand(TreeExpansionEvent e)

throws ExpandVetoException {

saySomething("You are about to expand node ", e);

int n = JOptionPane.showOptionDialog(

this, willExpandText, willExpandTitle,

JOptionPane.YES_NO_OPTION,

JOptionPane.QUESTION_MESSAGE,

null,

willExpandOptions,

willExpandOptions[1]);

LoadLazyChildren();

}

Running Codes

http://docs.oracle.com/javase/tutorial/uiswing/components/tree.html#create