final - Page 6 - Developer IT

private constructor and final

- by rest_day

Why is it a good practice to mark a class with only private constructors as final? My guess is, it is to let other programmers know that it cannot be sub-classed.

Multiple Components in a JTree Node Renderer & Node Editor

I am attempting to create a JTree where a node has several components: a JPanel that holds a JCheckBox, followed by a JLabel, then a JComboBox. I have attached the code at the bottom if one wishes to run it. Fortunately the JTree correctly renders the components. However when I click on the JComboBox, the node disappears; if I click on the JCheckBox, it works fine. It seems that I am doing something wrong with how the TreeCellEditor is being set up. How could I resolve this issue? Am I going beyond the capabilities of JTree? Here's a quick overview of the code I have posted below. The class EntityListDialog merely creates the user interface. It is not useful to understand it other than the createTree method. Node is the data structure that holds information about each node in the JTree. All Nodes have a name, but samples may be null or an empty array. This should be evident by looking at EntityListDialog's createTree method. The name is used as the text of the JCheckBox. If samples is non-empty, it is used as the contents of the JCheckBox. NodeWithSamplesRenderer renders Nodes whose samples are non-empty. It creates the complicated user interface with the JPanel consisting of the JCheckBox and the JComboBox. NodeWithoutSamplesRenderer creates just a JCheckBox when samples is empty. RendererDispatcher decides whether to use a NodeWithSamplesRenderer or a NodeWithoutSamplesRenderer. This entirely depends on whether Node has a non-empty samples member or not. It essentially functions as a means for the NodeWith*SamplesRenderer to plug into the JTree. Code listing: import java.awt.*; import java.awt.event.*; import java.util.*; import javax.swing.*; import javax.swing.tree.*; public class EntityListDialog { final JDialog dialog; final JTree entitiesTree; public EntityListDialog() { dialog = new JDialog((Frame) null, "Test"); entitiesTree = createTree(); JScrollPane entitiesTreeScrollPane = new JScrollPane(entitiesTree); JCheckBox pathwaysCheckBox = new JCheckBox("Do additional searches"); JButton sendButton = new JButton("Send"); JButton cancelButton = new JButton("Cancel"); JButton selectAllButton = new JButton("All"); JButton deselectAllButton = new JButton("None"); dialog.getContentPane().setLayout(new GridBagLayout()); GridBagConstraints c = new GridBagConstraints(); JPanel selectPanel = new JPanel(new FlowLayout(FlowLayout.LEFT)); selectPanel.add(new JLabel("Select: ")); selectPanel.add(selectAllButton); selectPanel.add(deselectAllButton); c.gridx = 0; c.gridy = 0; c.weightx = 1.0; c.weighty = 0.0; c.fill = GridBagConstraints.HORIZONTAL; dialog.getContentPane().add(selectPanel, c); c.gridx = 0; c.gridy = 1; c.weightx = 1.0; c.weighty = 1.0; c.fill = GridBagConstraints.BOTH; c.insets = new Insets(0, 5, 0, 5); dialog.getContentPane().add(entitiesTreeScrollPane, c); c.gridx = 0; c.gridy = 2; c.weightx = 1.0; c.weighty = 0.0; c.insets = new Insets(0, 0, 0, 0); c.fill = GridBagConstraints.HORIZONTAL; dialog.getContentPane().add(pathwaysCheckBox, c); JPanel buttonsPanel = new JPanel(new FlowLayout(FlowLayout.RIGHT)); buttonsPanel.add(sendButton); buttonsPanel.add(cancelButton); c.gridx = 0; c.gridy = 3; c.weightx = 1.0; c.weighty = 0.0; c.fill = GridBagConstraints.HORIZONTAL; dialog.getContentPane().add(buttonsPanel, c); dialog.pack(); dialog.setVisible(true); } public static void main(String[] args) { EntityListDialog dialog = new EntityListDialog(); } private static JTree createTree() { DefaultMutableTreeNode root = new DefaultMutableTreeNode( new Node("All Entities")); root.add(new DefaultMutableTreeNode( new Node("Entity 1", "Sample A", "Sample B", "Sample C"))); root.add(new DefaultMutableTreeNode( new Node("Entity 2", "Sample D", "Sample E", "Sample F"))); root.add(new DefaultMutableTreeNode( new Node("Entity 3", "Sample G", "Sample H", "Sample I"))); JTree tree = new JTree(root); RendererDispatcher rendererDispatcher = new RendererDispatcher(tree); tree.setCellRenderer(rendererDispatcher); tree.setCellEditor(rendererDispatcher); tree.setEditable(true); return tree; } } class Node { final String name; final String[] samples; boolean selected; int selectedSampleIndex; public Node(String name, String... samples) { this.name = name; this.selected = false; this.samples = samples; if (samples == null) { this.selectedSampleIndex = -1; } else { this.selectedSampleIndex = 0; } } public boolean isSelected() { return selected; } public void setSelected(boolean selected) { this.selected = selected; } public String toString() { return name; } public int getSelectedSampleIndex() { return selectedSampleIndex; } public void setSelectedSampleIndex(int selectedSampleIndex) { this.selectedSampleIndex = selectedSampleIndex; } public String[] getSamples() { return samples; } } interface Renderer { public void setForeground(final Color foreground); public void setBackground(final Color background); public void setFont(final Font font); public void setEnabled(final boolean enabled); public Component getComponent(); public Object getContents(); } class NodeWithSamplesRenderer implements Renderer { final DefaultComboBoxModel comboBoxModel = new DefaultComboBoxModel(); final JPanel panel = new JPanel(); final JCheckBox checkBox = new JCheckBox(); final JLabel label = new JLabel(" Samples: "); final JComboBox comboBox = new JComboBox(comboBoxModel); final JComponent components[] = {panel, checkBox, comboBox, label}; public NodeWithSamplesRenderer() { Boolean drawFocus = (Boolean) UIManager.get("Tree.drawsFocusBorderAroundIcon"); if (drawFocus != null) { checkBox.setFocusPainted(drawFocus.booleanValue()); } for (int i = 0; i < components.length; i++) { components[i].setOpaque(true); } panel.add(checkBox); panel.add(label); panel.add(comboBox); } public void setForeground(final Color foreground) { for (int i = 0; i < components.length; i++) { components[i].setForeground(foreground); } } public void setBackground(final Color background) { for (int i = 0; i < components.length; i++) { components[i].setBackground(background); } } public void setFont(final Font font) { for (int i = 0; i < components.length; i++) { components[i].setFont(font); } } public void setEnabled(final boolean enabled) { for (int i = 0; i < components.length; i++) { components[i].setEnabled(enabled); } } public void setContents(Node node) { checkBox.setText(node.toString()); comboBoxModel.removeAllElements(); for (int i = 0; i < node.getSamples().length; i++) { comboBoxModel.addElement(node.getSamples()[i]); } } public Object getContents() { String title = checkBox.getText(); String[] samples = new String[comboBoxModel.getSize()]; for (int i = 0; i < comboBoxModel.getSize(); i++) { samples[i] = comboBoxModel.getElementAt(i).toString(); } Node node = new Node(title, samples); node.setSelected(checkBox.isSelected()); node.setSelectedSampleIndex(comboBoxModel.getIndexOf(comboBoxModel.getSelectedItem())); return node; } public Component getComponent() { return panel; } } class NodeWithoutSamplesRenderer implements Renderer { final JCheckBox checkBox = new JCheckBox(); public NodeWithoutSamplesRenderer() { Boolean drawFocus = (Boolean) UIManager.get("Tree.drawsFocusBorderAroundIcon"); if (drawFocus != null) { checkBox.setFocusPainted(drawFocus.booleanValue()); } } public void setForeground(final Color foreground) { checkBox.setForeground(foreground); } public void setBackground(final Color background) { checkBox.setBackground(background); } public void setFont(final Font font) { checkBox.setFont(font); } public void setEnabled(final boolean enabled) { checkBox.setEnabled(enabled); } public void setContents(Node node) { checkBox.setText(node.toString()); } public Object getContents() { String title = checkBox.getText(); Node node = new Node(title); node.setSelected(checkBox.isSelected()); return node; } public Component getComponent() { return checkBox; } } class NoNodeRenderer implements Renderer { final JLabel label = new JLabel(); public void setForeground(final Color foreground) { label.setForeground(foreground); } public void setBackground(final Color background) { label.setBackground(background); } public void setFont(final Font font) { label.setFont(font); } public void setEnabled(final boolean enabled) { label.setEnabled(enabled); } public void setContents(String text) { label.setText(text); } public Object getContents() { return label.getText(); } public Component getComponent() { return label; } } class RendererDispatcher extends AbstractCellEditor implements TreeCellRenderer, TreeCellEditor { final static Color selectionForeground = UIManager.getColor("Tree.selectionForeground"); final static Color selectionBackground = UIManager.getColor("Tree.selectionBackground"); final static Color textForeground = UIManager.getColor("Tree.textForeground"); final static Color textBackground = UIManager.getColor("Tree.textBackground"); final JTree tree; final NodeWithSamplesRenderer nodeWithSamplesRenderer = new NodeWithSamplesRenderer(); final NodeWithoutSamplesRenderer nodeWithoutSamplesRenderer = new NodeWithoutSamplesRenderer(); final NoNodeRenderer noNodeRenderer = new NoNodeRenderer(); final Renderer[] renderers = { nodeWithSamplesRenderer, nodeWithoutSamplesRenderer, noNodeRenderer }; Renderer renderer = null; public RendererDispatcher(JTree tree) { this.tree = tree; Font font = UIManager.getFont("Tree.font"); if (font != null) { for (int i = 0; i < renderers.length; i++) { renderers[i].setFont(font); } } } public Component getTreeCellRendererComponent(JTree tree, Object value, boolean selected, boolean expanded, boolean leaf, int row, boolean hasFocus) { final Node node = extractNode(value); if (node == null) { renderer = noNodeRenderer; noNodeRenderer.setContents(tree.convertValueToText( value, selected, expanded, leaf, row, false)); } else { if (node.getSamples() == null || node.getSamples().length == 0) { renderer = nodeWithoutSamplesRenderer; nodeWithoutSamplesRenderer.setContents(node); } else { renderer = nodeWithSamplesRenderer; nodeWithSamplesRenderer.setContents(node); } } renderer.setEnabled(tree.isEnabled()); if (selected) { renderer.setForeground(selectionForeground); renderer.setBackground(selectionBackground); } else { renderer.setForeground(textForeground); renderer.setBackground(textBackground); } renderer.getComponent().repaint(); renderer.getComponent().invalidate(); renderer.getComponent().validate(); return renderer.getComponent(); } public Component getTreeCellEditorComponent( JTree tree, Object value, boolean selected, boolean expanded, boolean leaf, int row) { return getTreeCellRendererComponent( tree, value, true, expanded, leaf, row, true); } public Object getCellEditorValue() { return renderer.getContents(); } public boolean isCellEditable(final EventObject event) { if (!(event instanceof MouseEvent)) { return false; } final MouseEvent mouseEvent = (MouseEvent) event; final TreePath path = tree.getPathForLocation( mouseEvent.getX(), mouseEvent.getY()); if (path == null) { return false; } Object node = path.getLastPathComponent(); if (node == null || (!(node instanceof DefaultMutableTreeNode))) { return false; } DefaultMutableTreeNode treeNode = (DefaultMutableTreeNode) node; Object userObject = treeNode.getUserObject(); return (userObject instanceof Node); } private static Node extractNode(Object value) { if ((value != null) && (value instanceof DefaultMutableTreeNode)) { DefaultMutableTreeNode node = (DefaultMutableTreeNode) value; Object userObject = node.getUserObject(); if ((userObject != null) && (userObject instanceof Node)) { return (Node) userObject; } } return null; } }

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