1. Metric Converter What layout do we use? What is the class hierarchy?
The code for this application is on our class web-site
What layout do we use?
What is the class hierarchy?
What listeners do we use?

2. On-line Ordering Applet
The code for this application is on our class web-site
What layout do we use?
What is the class hierarchy?
What listeners do we use?

3. Simple Text Editor Allows simple text editing What layout do we use?
The code for this application is on our class web-site
Allows simple text editing
What layout do we use?
What is the class hierarchy?
What listeners do we use?

4. Trees Graph: Collection of nodes and edges
Nodes are the objects that hold data
Edges are links between nodes
Tree: A graph without cycles
Root: A distinguished node at the top of the tree
Purpose
Trees and graphs are probably the most used data structures in Computer Science
They are useful to represent
Directory structures
Discussion forums
Simulation of weather, climate change, global positioning
Relational databases

5. Lab Project The main frame has a border layout
Create a GUI that displays and modify a tree
The main frame has a border layout
The North section has a JTabbedPane
The Center section has a JScrollPane showing a JTree
The South section has a label that displays user help messages

6. Sample JTree Methods More information is in the lab instructions
JTree related classes
JTree (Java tree class)
DefaultTreeModel (Object that controls how tree displays)
DefaultMutableTreeNode (nodes to hold data in the tree)
Instantiate
A Node for the tree: root = new DefaultMutableTreeNode(“name”);
Tree Model: treeModel = new DefaultTreeModel(root);
A JTree: tree = Jtree(treeModel);
Add a node to the root, make it display, and highlight the new node
root.add(new DefaultMutableTreeNode("child node");
tree.scrollPathToVisible(new TreePath(child.getPath()));
treeModel.nodeStructureChanged(parent);
tree.setSelectionPath( (newTreePath(node.getPath())));
Display tree: for (int r=0; r<tree.getRowCount()-1; r++) tree.expandRow(r);
Collapse tree: for (int r=tree.getRowCount()-1;r>=0;r--) tree.collapseRow(r);
More information is in the lab instructions

7. Additional JTree methods
Path TreePath(node.getPath()); gets a path of nodes from root to node.
Tree.scrollPathToVisible(path); makes a path visible on the display.
treeModel.nodeStructureChanged(node); forces a node to be displayed.
treeModel.removeNodeFromParent(node); removes a node from the tree.
Node.getParent() gets the parent node.
(DefaultMutableTreeNode)tree.getLastSelectedPathComponent() can be used to get the node which is selected
Tree.setSelectionPath(new TreePath(node.getPath()) sets the selected node.
Node.setUserObject(“new name”) changes the node’s text.
treeModel.nodeChanged(node); to force a modified node to display
Tree.expandPath(path) and Tree.collapse(path)

8. Sample JTree Code Instantiate and Attach a listener
DefaultMutableTreeNode root = new DefaultMutableTreeNode(“Root”);
DefaultTreeModel treeModel = new DefaultTreeModel(root);
JTree tree = new JTree(treeModel);
tree.addTreeSelectionListener(this);
Initially fill tree with nodes int childName = 0;
For (int childX=1; childX<=4; childX++)
{ child = new DefaultMutableTreeNode
(“Node “ + childName++);
root.add(child);
for (int grandX=1; grandX<=4; grandX++)
{ grandChild = new DefaultMutableTreeNode
(“Node “+childName++);
child.add(grandChild);
} }

9. A Tabbed Panel Instantiate a TabbedPane Add a panel to the tabbed pane
JTabbedPane tabs = new JTabbedPane();
Add a panel to the tabbed pane
JPanel treeChanges = new TreeChangePanel();
tabs.addTab(“Modify”, treeChanges);
Set which pane shows initially
tabs.setSelectedIndex(0);

10. Containers Class Signature line
Public class TreeChangePanel implements ActionListener
Access to the JTree and other instance variables
Alternative1: Pass references to the constructor
Alternative 2: Nest Panel classes within the main class
Set Layout in the TreeChanges class
setLayout(new BoxLayout(this, BoxLayout,X_AXIS) );
Create and add the buttons
JButton addButton = new JButton("Add");
add(addButton);
Attach the listener
addActionListener(this);

11. The ActionListener Signature line Determine which button was clicked
public void actionPerformed(ActionEvent ae)
Determine which button was clicked
Alternative 1: if (ae.getSource()==addButton)
Alternative 2: JButton button = (JButton)ae.getSource(); if (button.getText()=="Add")
Event specific logic (for the 'add' option)
Set error label if a tree node is not selected
Create a new node
Add the new node to the node that is selected
Set the path to the new node visible
Indicate that the tree structure changed
Select the node just added

12. TreeSelectionListener
This listener responds to changes in the JTree structure
The valueChanged method handles the event
It's purpose is to set the label field to the node that the user selects
The initial version in the lab instructions can trigger a NullPointeException if there is no node selected
How do we get around this?
If there is no last selected path component, don't try to call the toString() method.