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GUI Tree Modification with JTree Sample Code

Explore how to create a GUI that displays and edits a tree using JTree sample methods and additional functionalities in Java. Learn about JTree related classes and customization options.

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GUI Tree Modification with JTree Sample Code

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

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

  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.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 nodesint 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 • 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()=="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.

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