Metric Converter

1
Metric Converter
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
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
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

• 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.getPat
  h()))
• treeModel.nodeStructureChanged(parent)
• tree.setSelectionPath( (newTreePath(node.getPath()
  )))
• Display tree for (int r0 rlttree.getRowCount()-1
  r) tree.expandRow(r)
• Collapse tree for (int rtree.getRowCount()-1rgt
  0r--) 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.getLastSelectedPathCo
  mponent() 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 nodes
  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 childX1 childXlt4 childX)
• child new DefaultMutableTreeNode
• (Node childName)
• root.add(child)
• for (int grandX1 grandXlt4 grandX)
• grandChild new DefaultMutableTreeNode
• (Node
  childName)
• child.add(grandChild)

9
A Tabbed Panel

• Instantiate a TabbedPane
• 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
• 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()"Ad
  d")
• 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.