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How to Use Tables - Java Tutorial 5.0 英文版

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Trail: Creating a GUI with JFC/Swing
Lesson: Using Swing Components

How to Use Tables

With the JTable class you can display tables of data, optionally allowing the user to edit the data. JTable doesn't contain or cache data; it's simply a view of your data. Here's a picture of a typical table displayed within a scroll pane:

[PENDING: Update this snapshot.

Label these parts:
- each cell displays an item of data
- each column header describes its column
maybe also have these labels: 
- each column contains one type of data
- a table header displays the column headers]

The rest of this section tells you how to accomplish some common table-related tasks. Here are the topics this section covers:

• Creating a Simple Table
• Adding a Table to a Container
• Setting and Changing Column Widths
• Detecting User Selections
• Creating a Table Model
• Detecting Data Changes
• Concepts: Editors and Renderers
• Using a Combo Box as an Editor
• Using an Editor to Validate User-Entered Text
• Using Other Editors
• Using Custom Renderers
• Specifying Tool Tips for Cells
• Specifying Tool Tips for Column Headers
• Sorting and Otherwise Manipulating Data
• The Table API
• Examples that Use Tables

Creating a Simple Table

[PENDING: This figure will be updated.]

---

Try this: 

1. Run SimpleTableDemo using Java^TM Web Start. Or, to compile and run the example yourself, consult the example index.
2. Click the cell that contains "Snowboarding".
   The entire first row is selected, indicating that you have selected Mary Campione's data. A special highlight indicates that the "Snowboarding" cell is editable. Generally, you begin editing a text cell by double-clicking it.
3. Position the cursor over "First Name". Now press the mouse button and drag to the right.
   As you can see, users can rearrange columns in tables.
4. Position the cursor just to the right of a column header. Now press the mouse button and drag to the right or left.
   The column changes size, and the other columns adjust to fill the remaining space.
5. Resize the window containing the table so that it's bigger than necessary to display the whole table.
   All the table cells become wider, expanding to fill the extra horizontal space.

---

Here is the code that implements the table in SimpleTableDemo.java:

String[] columnNames = {"First Name",
                        "Last Name",
                        "Sport",
                        "# of Years",
                        "Vegetarian"};

Object[][] data = {
    {"Mary", "Campione",
     "Snowboarding", new Integer(5), new Boolean(false)},
    {"Alison", "Huml",
     "Rowing", new Integer(3), new Boolean(true)},
    {"Kathy", "Walrath",
     "Knitting", new Integer(2), new Boolean(false)},
    {"Sharon", "Zakhour",
     "Speed reading", new Integer(20), new Boolean(true)},
    {"Philip", "Milne",
     "Pool", new Integer(10), new Boolean(false)}
};

JTable table = new JTable(data, columnNames);

The SimpleTableDemo example uses one of two JTable constructors that directly accept data:

• JTable(Object[][] rowData, Object[] columnNames)
• JTable(Vector rowData, Vector columnNames)

The advantage of these constructors is that they're easy to use. However, these constructors also have disadvantages:

• They automatically make every cell editable.
• They treat all data types the same (as strings). For example, if a table column has Boolean data, the table can display the data in a check box. However, if you use one of the two JTable constructors listed previously, your Boolean data will be displayed as a string. You can see this difference in the last column of the two previous pictures of tables.
• They require that you put all of the table's data in an array or vector, which isn't appropriate for some data. For example, if you're instantiating a set of objects from a database, you might want to query the objects directly for their values, rather than copying all their values into an array or vector.

If you want to get around these restrictions, you need to implement your own table model, as described in Creating a Table Model.

Adding a Table to a Container

It's easy to put a table in a scroll pane. You need just one or two lines of code:

JScrollPane scrollPane = new JScrollPane(table);
table.setPreferredScrollableViewportSize(new Dimension(500, 70));

The scroll pane automatically gets the table's header, which displays the column names, and puts it on top of the table. Even when the user scrolls down, the column names remain visible at the top of the viewing area. The scroll pane also tries to make its viewing area the same as the table's preferred viewing size. The previous code snippet sets the table's preferred viewing size with the setPreferredScrollableViewportSize method.

If you're using a table without a scroll pane, then you must get the table header component and place it yourself. For example:

container.setLayout(new BorderLayout());
container.add(table.getTableHeader(), BorderLayout.PAGE_START);
container.add(table, BorderLayout.CENTER);

Setting and Changing Column Widths

By default, all columns in a table start out with equal width, and the columns automatically fill the entire width of the table. When the table becomes wider or narrower (which might happen when the user resizes the window containing the table), all the column widths change appropriately.

When the user resizes a column by dragging its right border, then either other columns must change size, or the table's size must change. By default, the table's size remains the same, and all columns to the right of the drag point resize to accommodate space added to or removed from the column to the left of the drag point.

The following figures illustrate the default resizing behavior. [PENDING: These will be updated.]

Initially, the columns have equal width.

When the user resizes a column, some of the other columns must adjust size for the table to stay the same size.

When the entire table is resized, all the columns are resized.

To customize initial column widths, you can invoke setPreferredWidth on each of your table's columns. This sets both the preferred widths of the columns and their approximate relative widths. For example, adding the following code to SimpleTableDemo makes its third column bigger than the other columns:

TableColumn column = null;
for (int i = 0; i < 5; i++) {
    column = table.getColumnModel().getColumn(i);
    if (i == 2) {
        column.setPreferredWidth(100); //sport column is bigger
    } else {
        column.setPreferredWidth(50);
    }
}

As the preceding code shows, each column in a table is represented by a TableColumn object. TableColumn supplies getter and setter methods for the minimum, preferred, and maximum widths of a column, as well as a method for getting the current width. For an example of setting cell widths based on the actual amount of space needed to draw the cells' contents, see the initColumnSizes method in TableRenderDemo.java.

When the user explicitly resizes columns, the columns' preferred widths are set such that the user-specified sizes become the columns' new current widths. However, when table itself is resized — typically because the window has resized — the columns' preferred widths do not change. Instead, the existing preferred widths are used to calculate new column widths to fill the available space.

You can change a table's resize behavior by invoking the setAutoResizeMode method. The method's argument should have one of these values (defined as constants in JTable):

AUTO_RESIZE_SUBSEQUENT_COLUMNS

The default. In addition to resizing the column to the left of the drag point, adjusts the sizes of all columns to the right of the drag point.

AUTO_RESIZE_NEXT_COLUMN

Adjusts only the columns immediately to the left and right of the drag point.

AUTO_RESIZE_OFF

Adjusts the table size instead.

Detecting User Selections

The following code snippet shows how to detect when the user selects a table row. By default, a table allows the user to select multiple rows — not columns or individual cells — and the selected rows need not be next to each other. Using the setSelectionMode method, the following code specifies that only one row at a time can be selected.

table.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
...
//Ask to be notified of selection changes.
ListSelectionModel rowSM = table.getSelectionModel();
rowSM.addListSelectionListener(new ListSelectionListener() {
    public void valueChanged(ListSelectionEvent e) {
        //Ignore extra messages.
        if (e.getValueIsAdjusting()) return;

        ListSelectionModel lsm =
            (ListSelectionModel)e.getSource();
        if (lsm.isSelectionEmpty()) {
            ...//no rows are selected
        } else {
            int selectedRow = lsm.getMinSelectionIndex();
            ...//selectedRow is selected
        }
    }
});

The code is from SimpleTableSelectionDemo.java. SimpleTableSelectionDemo also has code (not included in the preceding snippet) that changes the table's selection orientation. By changing a couple of boolean values, you can make the table allow either column selections or individual cell selections, instead of row selections.

For more information and examples of implementing selection, see How to Write a List Selection Listener.

Creating a Table Model

As the following figure shows, every table gets its data from an object that implements the TableModel interface.

[PENDING: This figure might be updated to look more modern.]

The JTable constructor used by SimpleTableDemo creates its table model with code like this:

new AbstractTableModel() {
    public String getColumnName(int col) {
        return columnNames[col].toString();
    }
    public int getRowCount() { return rowData.length; }
    public int getColumnCount() { return columnNames.length; }
    public Object getValueAt(int row, int col) {
        return rowData[row][col];
    }
    public boolean isCellEditable(int row, int col)
        { return true; }
    public void setValueAt(Object value, int row, int col) {
        rowData[row][col] = value;
        fireTableCellUpdated(row, col);
    }
}

As the preceding code shows, implementing a table model can be simple. Generally, you implement your table model in a subclass of the AbstractTableModel class.

Your model might hold its data in an array, vector, or hash map, or it might get the data from an outside source such as a database. It might even generate the data at execution time.

Here again is a picture of a table implemented by TableDemo (which you can run using Java Web Start) that has a custom table model:

[PENDING: This figure will be updated.]

This table is different from the SimpleTableDemo table in the following ways:

• TableDemo's custom table model, even though it's simple, can easily determine the data's type, helping the JTable display the data in the best format. SimpleTableDemo's automatically created table model, on the other hand, isn't smart enough to know that the # of Years column contains numbers (which should generally be right aligned and have a particular format). It also doesn't know that the Vegetarian column contains boolean values, which can be represented by check boxes.
• In TableDemo, we implemented the custom table model so that it doesn't let you edit the name columns; it does, however, let you edit the other columns. In SimpleTableDemo, all cells are editable.

Below is the code from TableDemo.java that is different from the code in SimpleTableDemo.java. Bold font indicates the code that makes this table's model different from the table model defined automatically for SimpleTableDemo.

public TableDemo() {
    ...
    JTable table = new JTable(new MyTableModel());
    ...
}

class MyTableModel extends AbstractTableModel {
    private String[] columnNames = ...//same as before...
    private Object[][] data = ...//same as before...

    public int getColumnCount() {
        return columnNames.length;
    }

    public int getRowCount() {
        return data.length;
    }

    public String getColumnName(int col) {
        return columnNames[col];
    }

    public Object getValueAt(int row, int col) {
        return data[row][col];
    }

    public Class getColumnClass(int c) {
        return getValueAt(0, c).getClass();
    }

    /*
     * Don't need to implement this method unless your table's
     * editable.
     */
    public boolean isCellEditable(int row, int col) {
        //Note that the data/cell address is constant,
        //no matter where the cell appears onscreen.
        if (col < 2) {
            return false;
        } else {
            return true;
        }
    }

    /*
     * Don't need to implement this method unless your table's
     * data can change.
     */
    public void setValueAt(Object value, int row, int col) {
        data[row][col] = value;
        fireTableCellUpdated(row, col);
    }
    ...
}

Detecting Data Changes

A table and its model automatically detect whenever the user edits the table's data. However, if the data changes for another reason, you must take special steps to notify the table and its model of the data change. Also, if you don't implement a table model, as in SimpleTableDemo, then you must take special steps to find out when the user edits the table's data.

An example of updating a table's data without directly editing it is in the BINGO application. The BINGO application, which is presented in BINGO!, has a table that displays some information about each user who is signed up to play the game. When a new user signs up to play BINGO, the table needs to add a new row for that user. More precisely, the table model needs to get the data for the new user, and then the table model needs to tell the table to display the new data.

To notify the table model about a new user, the BINGO application invokes the table model's updatePlayer method. You can see the code for that method in PlayerInfoModel, which contains the implementation of the table model. The updatePlayer method records the new user's data and fires a table-model event. Because every table listens for table-model events from its model, the user-information table automatically detects the change and displays the new data.

To fire the table-model event, the model invokes the fireTableRowsInserted method, which is defined by the AbstractTableModel class. Other fireXxxx methods that AbstractTableModel defines are fireTableCellUpdated, fireTableChanged, fireTableDataChanged, fireTableRowsDeleted, fireTableRowsInserted, fireTableRowsUpdated, and fireTableStructureChanged.

If you have a class such as SimpleTableDemo that isn't a table or table model, but needs to react to changes in a table model, then you need to do something special to find out when the user edits the table's data. Specifically, you need to register a TableModelListener on the table model. Adding the bold code in the following snippet makes SimpleTableDemo react to table data changes.

import javax.swing.event.*;
import javax.swing.table.TableModel;

public class SimpleTableDemo ... implements TableModelListener {
    ...
    public SimpleTableDemo() {
        ...
        table.getModel().addTableModelListener(this);
        ...
    }

    public void tableChanged(TableModelEvent e) {
        int row = e.getFirstRow();
        int column = e.getColumn();
        TableModel model = (TableModel)e.getSource();
        String columnName = model.getColumnName(column);
        Object data = model.getValueAt(row, column);

        ...// Do something with the data...
    }
    ...
}

Concepts: Editors and Renderers

Before you go on to the next few tasks, you need to understand how tables draw their cells. You might expect each cell in a table to be a component. However, for performance reasons, Swing tables aren't implemented that way.

Instead, a single cell renderer is generally used to draw all of the cells that contain the same type of data. You can think of the renderer as a configurable ink stamp that the table uses to stamp appropriately formatted data onto each cell. When the user starts to edit a cell's data, a cell editor takes over the cell, controlling the cell's editing behavior.

For example, each cell in the # of Years column in TableDemo contains Number data — specifically, an Integer object. By default, the cell renderer for a Number-containing column uses a single JLabel instance to draw the appropriate numbers, right-aligned, on the column's cells. If the user begins editing one of the cells, the default cell editor uses a right-aligned JTextField to control the cell editing.

To choose the renderer that displays the cells in a column, a table first determines whether you specified a renderer for that particular column. (We'll tell you how to specify renderers a bit later.) If you didn't, then the table invokes the table model's getColumnClass method, which gets the data type of the column's cells. Next, the table compares the column's data type with a list of data types for which cell renderers are registered. This list is initialized by the table, but you can add to it or change it. Currently, tables put the following types of data in the list:

• Boolean — rendered with a check box.
• Number — rendered by a right-aligned label.
• Double, Float — same as Number, but the object-to-text translation is performed by a NumberFormat instance (using the default number format for the current locale).
• Date — rendered by a label, with the object-to-text translation performed by a DateFormat instance (using a short style for the date and time).
• ImageIcon, Icon — rendered by a centered label.
• Object — rendered by a label that displays the object's string value.

---

Version note: The default renderer associations for Double, Float, and Icon were added in 1.3.

---

Cell editors are chosen using a similar algorithm.

Remember that if you let a table create its own model, it uses Object as the type of every column. To specify more precise column types, the table model must define the getColumnClass method appropriately, as demonstrated by TableDemo.java.

Keep in mind that although renderers determine how each cell or column header looks and can specify its tool tip text, renderers don't handle events. If you need to pick up the events that take place inside a table, the technique you use varies by the sort of event you're interested in:

Situation	How to Get Events
To detect events from a cell that's being edited...	Use the cell editor (or register a listener on the cell editor).
To detect row/column/cell selections and deselections...	Use a selection listener as described in Detecting User Selections.
To detect mouse events on a column header...	Register the appropriate type of mouse listener on the table's JTableHeader object. (See TableSorter.java for an example.)
To detect other events...	Register the appropriate listener on the JTable object.

The next few sections tell you how to customize display and editing by specifying renderers and editors. You can specify cell renderers and editors either by column or by data type.

Using a Combo Box as an Editor

Setting up a combo box as an editor is simple, as the following example shows. The bold line of code sets up the combo box as the editor for a specific column.

TableColumn sportColumn = table.getColumnModel().getColumn(2);
...
JComboBox comboBox = new JComboBox();
comboBox.addItem("Snowboarding");
comboBox.addItem("Rowing");
comboBox.addItem("Chasing toddlers");
comboBox.addItem("Speed reading");
comboBox.addItem("Teaching high school");
comboBox.addItem("None");
sportColumn.setCellEditor(new DefaultCellEditor(comboBox));

Here is a picture of the combo box editor in use:

[PENDING: This figure will be updated. It should probably include the cursor.]

The preceding code is from TableRenderDemo.java. You can run TableRenderDemo using Java Web Start.

Using an Editor to Validate User-Entered Text

If a cell's default editor allows text entry, you get some error checking for free if the cell's type is specified as something other than String or Object. The error checking is a side effect of converting the entered text into an object of the proper type.

---

Version note: Before 1.3, the default implementation did not in any way restrict the string that could be entered, and didn't convert it from a String. You needed to put some ugly code in the model's setValueAt method to parse the entered string and prevent the cell's value from becoming a String.

---

The automatic checking of user-entered strings occurs when the default editor attempts to create a new instance of the class associated with the cell's column. The default editor creates this instance using a constructor that takes a String as an argument. For example, in a column whose cells have type Integer, when the user types in "123" the default editor creates the corresponding Integer using code equivalent to new Integer("123"). If the constructor throws an exception, the cell's outline turns red and refuses to let focus move out of the cell. If you implement a class used as a column data type, you can use the default editor if your class supplies a constructor that takes a single argument of type String.

If you like having a text field as the editor for a cell, but want to customize it — perhaps to check user-entered text more strictly or to react differently when the text is invalid — you can change the cell editor to use a formatted text field. The formatted text field can check the value either continuously while the user is typing or after the user has indicated the end of typing (such as by pressing Enter).

The following code, taken from a demo named TableFTFEditDemo, sets up a formatted text field as an editor that limits all integer values to be between 0 and 100. You can run TableFTFEditDemo using Java Web Start. The following code makes the formatted text field the editor for all columns that contain data of type Integer.

table.setDefaultEditor(Integer.class,
                       new IntegerEditor(0, 100));

The IntegerEditor class is implemented as a subclass of DefaultCellEditor that uses a JFormattedTextField instead of the JTextField that DefaultCellEditor supports. It accomplishes this by first setting up a formatted text field to use an integer format and have the specified minimum and maximum values, using the API described in How to Use Formatted Text Fields. It then overrides the DefaultCellEditor implementation of the getTableCellEditorComponent, getCellEditorValue, and stopCellEditing methods, adding the operations that are necessary for formatted text fields.

The override of getTableCellEditorComponent sets the formatted text field's value property (and not just the text property it inherits from JTextField) before the editor is shown. The override of getCellEditorValue keeps the cell value as an Integer, rather than, say, the Long value that the formatted text field's parser tends to return. Finally, overriding stopCellEditing lets us check whether the text is valid, possibly stopping the editor from being dismissed. If the text isn't valid, our implementation of stopCellEditing puts up a dialog that gives the user the option of continuing to edit or reverting to the last good value. The source code is a bit too long to include here, but you can find it in IntegerEditor.java.

Using Other Editors

Whether you're setting the editor for a single column of cells (using the TableColumn setCellEditor method) or for a specific type of data (using the JTable setDefaultEditor method), you specify the editor using an argument that adheres to the TableCellEditor interface. Fortunately, the DefaultCellEditor class implements this interface and provides constructors to let you specify an editing component that's a JTextField, JCheckBox, or JComboBox. You usually don't have to explicitly specify a check box as an editor, since columns with Boolean data automatically use a check box renderer and editor.

What if you want to specify an editor that isn't a text field, check box, or combo box? Well, because DefaultCellEditor doesn't support other types of components, you must do a little more work. You need to create a class that implements the TableCellEditor interface. The AbstractCellEditor class is a good superclass to use. It implements TableCellEditor's superinterface, CellEditor, saving you the trouble of implementing the event firing code necessary for cell editors.

Your cell editor class needs to define at least two methods — getCellEditorValue and getTableCellEditorComponent. The getCellEditorValue method, required by CellEditor, returns the cell's current value. The getTableCellEditorComponent method, required by TableCellEditor, should configure and return the component that you want to use as the editor.

---

Version note: The AbstractCellEditor class was added in 1.3. Before then, implementing a cell editor for a new component type was much more difficult, since you had to implement all the CellEditor methods yourself.

---

Here is a picture of a table with a dialog that serves, indirectly, as a cell editor. When the user begins editing a cell in the Favorite Color column, a button (the true cell editor) appears and brings up the dialog, with which the user can choose a different color.

[PENDING: This figure will be updated.]

You can run TableDialogEditDemo using Java Web Start, or compile and run it yourself by consulting the example index. Here is the code, taken from ColorEditor.java, that implements the cell editor.

public class ColorEditor extends AbstractCellEditor
                         implements TableCellEditor,
                                    ActionListener {
    Color currentColor;
    JButton button;
    JColorChooser colorChooser;
    JDialog dialog;
    protected static final String EDIT = "edit";

    public ColorEditor() {
        button = new JButton();
        button.setActionCommand(EDIT);
        button.addActionListener(this);
        button.setBorderPainted(false);

        //Set up the dialog that the button brings up.
        colorChooser = new JColorChooser();
        dialog = JColorChooser.createDialog(button,
                                        "Pick a Color",
                                        true,  //modal
                                        colorChooser,
                                        this,  //OK button handler
                                        null); //no CANCEL button handler
    }

    public void actionPerformed(ActionEvent e) {
        if (EDIT.equals(e.getActionCommand())) {
            //The user has clicked the cell, so
            //bring up the dialog.
            button.setBackground(currentColor);
            colorChooser.setColor(currentColor);
            dialog.setVisible(true);

            fireEditingStopped(); //Make the renderer reappear.

        } else { //User pressed dialog's "OK" button.
            currentColor = colorChooser.getColor();
        }
    }

    //Implement the one CellEditor method that AbstractCellEditor doesn't.
    public Object getCellEditorValue() {
        return currentColor;
    }

    //Implement the one method defined by TableCellEditor.
    public Component getTableCellEditorComponent(JTable table,
                                                 Object value,
                                                 boolean isSelected,
                                                 int row,
                                                 int column) {
        currentColor = (Color)value;
        return button;
    }
}

As you can see, the code is pretty simple. The only part that's a bit tricky is the call to fireEditingStopped at the end of the editor button's action handler. Without this call, the editor would remain active, even though the modal dialog is no longer visible. The call to fireEditingStopped lets the table know that it can deactivate the editor, letting the cell be handled by the renderer again.

Using Custom Renderers

This section tells you how to create and specify a cell renderer. You can set a type-specific cell renderer using the JTable method setDefaultRenderer. To specify that cells in a particular column should use a renderer, you use the TableColumn method setCellRenderer. You can even specify a cell-specific renderer by creating a JTable subclass, as we'll show later.

It's easy to customize the text or image rendered by the default renderer, DefaultTableCellRenderer. You just create a subclass and implement the setValue method so that it invokes setText or setIcon with the appropriate string or image. For example, here is how the default date renderer is implemented:

static class DateRenderer extends DefaultTableCellRenderer {
    DateFormat formatter;
    public DateRenderer() { super(); }

    public void setValue(Object value) {
        if (formatter==null) {
            formatter = DateFormat.getDateInstance();
        }
        setText((value == null) ? "" : formatter.format(value));
    }
}

If extending DefaultTableCellRenderer doesn't do the trick, you can build a renderer using another superclass. The easiest way is to create a subclass of an existing component, making your subclass implement the TableCellRenderer interface. TableCellRenderer requires just one method: getTableCellRendererComponent. Your implementation of this method should set up the rendering component to reflect the passed-in state, and then return the component.

In the preceding snapshot of TableDialogEditDemo, the renderer used for Favorite Color cells is a subclass of JLabel called ColorRenderer. Here are excerpts from ColorRenderer.java that show how it's implemented.

public class ColorRenderer extends JLabel
                           implements TableCellRenderer {
    ...
    public ColorRenderer(boolean isBordered) {
        this.isBordered = isBordered;
        setOpaque(true); //MUST do this for background to show up.
    }

    public Component getTableCellRendererComponent(
                            JTable table, Object color,
                            boolean isSelected, boolean hasFocus,
                            int row, int column) {
        Color newColor = (Color)color;
        setBackground(newColor);
        if (isBordered) {
            if (isSelected) {
                ...
                //selectedBorder is a solid border in the color
                //table.getSelectionBackground().
                setBorder(selectedBorder);
            } else {
                ...
                //unselectedBorder is a solid border in the color
                //table.getBackground().
                setBorder(unselectedBorder);
            }
        }
        
        setToolTipText(...); //Discussed in the following section
        return this;
    }
}

Here is the code from TableDialogEditDemo.java that registers a ColorRenderer instance as the default renderer for all Color data:

table.setDefaultRenderer(Color.class, new ColorRenderer(true));

The next section shows a couple of examples of using TableColumn's setCellRenderer method, so we'll skip that for now and show you how to specify a renderer for a particular cell. To specify a cell-specific renderer, you need to define a JTable subclass that overrides the getCellRenderer method. For example, the following code makes the first cell in the first column of the table use a custom renderer:

TableCellRenderer weirdRenderer = new WeirdRenderer();
table = new JTable(...) {
    public TableCellRenderer getCellRenderer(int row, int column) {
        if ((row == 0) && (column == 0)) {
            return weirdRenderer;
        }
        // else...
        return super.getCellRenderer(row, column);
    }
};

Specifying Tool Tips for Cells

By default, the tool tip text displayed for a table cell is determined by the cell's renderer. However, sometimes it can be simpler to specify tool tip text by overriding JTable's implementation of the getToolTipText(MouseEvent) method. This section tells you how to use both techniques.

To add a tool tip to a cell using its renderer, you first need to get or create the cell renderer. Then, after making sure the rendering component is a JComponent, invoke the setToolTipText method on it.

An example of setting tool tips for cells is in TableRenderDemo, which you can run using Java Web Start. The source code is in TableRenderDemo.java. It adds tool tips to the cells of the Sport column with the following code:

//Set up tool tips for the sport cells.
DefaultTableCellRenderer renderer =
        new DefaultTableCellRenderer();
renderer.setToolTipText("Click for combo box");
sportColumn.setCellRenderer(renderer);

Here is a picture of the resulting tool tip:

[PENDING: We will put a picture here. It might be cropped to just include the relevant cell and its tool tip (along with whatever other cells are between them).]

Although the tool tip text in the previous example is static, you can also implement tool tips whose text changes depending on the state of the cell or program. Here are a couple ways to do so:

• Add a bit of code to the renderer's implementation of the getTableCellRendererComponent method.
• Override the JTable method getToolTipText(MouseEvent).

An example of adding code to a cell renderer is in TableDialogEditDemo (which you can run using Java Web Start). TableDialogEditDemo uses a renderer for colors, implemented in ColorRenderer.java, that sets the tool tip text using the boldface code in the following snippet:

public class ColorRenderer extends JLabel 
                           implements TableCellRenderer {
    ...
    public Component getTableCellRendererComponent(
                            JTable table, Object color,
                            boolean isSelected, boolean hasFocus,
                            int row, int column) {
        Color newColor = (Color)color;
        ...
        setToolTipText("RGB value: " + newColor.getRed() + ", "
                                     + newColor.getGreen() + ", "
                                     + newColor.getBlue());
        return this;
    }
}

Here is an example of what the tool tip looks like:

[PENDING: this snapshot needs to be updated. It should probably be cropped, as well.]

As we mentioned before, you can specify tool tip text by overriding JTable's getToolTipText(MouseEvent) method. The program TableToolTipsDemo shows how. You can run TableToolTipsDemo using Java Web Start. The cells with tool tips are in the Sport and Vegetarian columns. Here's are pictures of their tool tips:

[PENDING: put a picture here. It could be cropped to just include the relevant cell and its tool tip (along with whatever other cells are between them).]

[PENDING: this snapshot needs to be updated and cropped.]

Here is the code from TableToolTipsDemo.java that implements tool tips for cells in the Sport and Vegetarian columns:

JTable table = new JTable(new MyTableModel()) {    
    //Implement table cell tool tips.
    public String getToolTipText(MouseEvent e) {
        String tip = null;
        java.awt.Point p = e.getPoint();
        int rowIndex = rowAtPoint(p);
        int colIndex = columnAtPoint(p);
        int realColumnIndex = convertColumnIndexToModel(colIndex);

        if (realColumnIndex == 2) { //Sport column
            tip = "This person's favorite sport to "
                   + "participate in is: "
                   + getValueAt(rowIndex, colIndex);

        } else if (realColumnIndex == 4) { //Veggie column
            TableModel model = getModel();
            String firstName = (String)model.getValueAt(rowIndex,0);
            String lastName = (String)model.getValueAt(rowIndex,1);
            Boolean veggie = (Boolean)model.getValueAt(rowIndex,4);
            if (Boolean.TRUE.equals(veggie)) {
                tip = firstName + " " + lastName
                      + " is a vegetarian";
            } else {
                tip = firstName + " " + lastName
                      + " is not a vegetarian";
            }

        } else { //another column
            //You can omit this part if you know you don't 
            //have any renderers that supply their own tool 
            //tips.
            tip = super.getToolTipText(e);
        }
        return tip;
    }
    ...
}

The code is fairly straightforward, except perhaps for the call to convertColumnIndexToModel. That call is necessary because if the user moves the columns around, the view's index for the column doesn't match the model's index for the column. For example, the user might drag the Vegetarian column (which the model considers to be at index 4) so it's displayed as the first column — at view index 0. Since prepareRenderer gives us the view index, we need to translate the view index to a model index so we can be sure we're dealing with the intended column.

Specifying Tool Tips for Column Headers

You can add a tool tip to a column header by setting the tool tip text for the table's JTableHeader. Often, different column headers require different tool tip text. You can change the text by overriding the table header's getToolTipText(MouseEvent) method.

An example of using the same tool tip text for all column headers is in TableSorterDemo. Here is how it sets the tool tip text:

table.getTableHeader().setToolTipText(
        "Click to sort; Shift-Click to sort in reverse order");

TableToolTipsDemo has an example of implementing column header tool tips that vary by column. If you run TableToolTipsDemo, which you can do using Java Web Start, you'll see the tool tips when you mouse over any column header except for the first two. We elected not to supply tool tips for the name columns since they seemed self explanatory. (Actually, we just wanted to show you that it could be done.) Here's a picture of one of the column header tool tips:

[PENDING: this snapshot needs to be updated. It should also be cropped.]

The following code implements the tool tips. Basically, it creates a subclass of JTableHeader that overrides the getToolTipText(MouseEvent) method so that it returns the text for the current column. To associate the revised table header with the table, the JTable method createDefaultTableHeader is overridden so that it returns an instance of the JTableHeader subclass.

protected String[] columnToolTips = {
    null,
    null,
    "The person's favorite sport to participate in",
    "The number of years the person has played the sport",
    "If checked, the person eats no meat"};
...

JTable table = new JTable(new MyTableModel()) {
    ...

    //Implement table header tool tips.
    protected JTableHeader createDefaultTableHeader() {
        return new JTableHeader(columnModel) {
            public String getToolTipText(MouseEvent e) {
                String tip = null;
                java.awt.Point p = e.getPoint();
                int index = columnModel.getColumnIndexAtX(p.x);
                int realIndex = 
                        columnModel.getColumn(index).getModelIndex();
                return columnToolTips[realIndex];
            }
        };
    }
};

---

Version note: Before 1.3, each column had its own header renderer, and you could use the value returned by the TableColumn method getHeaderRenderer to set a tool tip for a specific column header. For performance reasons, the default behavior is now to use a single renderer for all column headers, and getHeaderRenderer returns null. The default header renderer used for all columns is returned by the TableHeader method getDefaultRenderer, which was added in 1.3.

---

Sorting and Otherwise Manipulating Data

One way to perform data manipulation such as sorting is to use one or more specialized table models (data manipulators), in addition to the table model that provides the data (the data model). The data manipulators should sit between the table and the data model, as the following picture shows:

[PENDING: This figure will be updated.]

If you decide to implement a data manipulator, take a look at TableMap.java and TableSorter.java. The TableMap class implements TableModel and serves as a superclass for data manipulators. TableSorter is a data manipulator that sorts the data provided by another table model. It used to be implemented as a subclass of TableMap, but now is a direct subclass of AbstractTableModel. You can use TableSorter as-is to provide sorting functionality, or you can use either TableSorter or TableMap as a basis for writing your own data manipulator.

To implement sorting with TableSorter, you need just three lines of code. The following listing shows the differences between TableDemo and its sorting cousin, TableSorterDemo.java.

TableSorter sorter = new TableSorter(new MyTableModel()); //ADDED THIS
//JTable table = new JTable(new MyTableModel());          //OLD
JTable table = new JTable(sorter);             //NEW
sorter.setTableHeader(table.getTableHeader()); //ADDED THIS

---

Note: The TableSorter class was updated in February, 2004. We recommend the newer version, as it has more features and fixes several bugs. If you currently use the old version, you can update to the new one by deleting TableMap.java and making the following change in the code that sets up the sorter:

//sorter.addMouseListenerToHeaderInTable(table); //OLD
sorter.setTableHeader(table.getTableHeader());   //NEW

---

The setTableHeader method sets up the table's column headers to detect user clicks and update the UI appropriately. When the user clicks, the sorter sorts the rows based on the clicked column. As the following snapshot shows, when you click "Last Name", the rows are reordered so that the row with "Campione" becomes the first row.

[PENDING: This figure will be updated.]

You can add secondary sorting by Control-clicking additional columns. For example, by clicking the Vegetarian column and then Control-clicking the Last Name column, you get an alphabetized listing of vegetarians followed by an alphabetized listing of omnivores.

[PENDING: We will add a figure showing secondary sorting.]

You can change the clicking behavior by reimplementing the MouseHandler class defined in TableSorter.java.

The Table API

The tables in this section cover just part of the table API. For more information about the table API, see the API documentation for JTable and for the various classes and interfaces in the table package. Also see The JComponent Class, which describes the API that JTable inherits from JComponent. The API for using tables falls into the following categories:

• Table-Related Classes and Interfaces
• Creating and Setting Up a Table
• Manipulating Columns
• Using Editors and Renderers
• Implementing Selection

Table-Related Classes and Interfaces

Class or Interface	Purpose
JTable	The component that presents the table to the user.
JTableHeader	The component that presents the column names to the user. By default, the table generates this component automatically.
TableModel AbstractTableModel	Respectively, the interface that a table model must implement and the usual superclass for table model implementations.
TableCellRenderer DefaultTableCellRenderer	Respectively, the interface that a table cell renderer must implement and the usual implementation used.
TableCellEditor DefaultCellEditor AbstractCellEditor	Respectively, the interface that a table cell editor must implement, the usual implementation used, and the usual superclass for table cell editor implementations.
TableColumnModel DefaultTableColumnModel	Respectively, the interface that a table column model must implement and the usual implementation used. You don't usually need to deal with the table column model directly unless you need to get the column selection model, or get a column index or object.
TableColumn	Controls all the attributes of a table column, including resizability; minimum, preferred, current, and maximum widths; and an optional column-specific renderer/editor.
DefaultTableModel	A Vector-based table model used by JTable when you construct a table specifying no data model and no data.
TableModelListener	The interface that an object must implement to be notified of changes to the TableModel.
ListSelectionListener	The interface that an object must implement to be notified of changes to the table's selection.

Creating and Setting Up a Table

Constructor or Method	Purpose
JTable(TableModel) JTable(TableModel, TableColumnModel) JTable(TableModel, TableColumnModel, ListSelectionModel) JTable() JTable(int, int) JTable(Object[][], Object[]) JTable(Vector, Vector)	Create a table. The optional TableModel argument specifies the model that provides the data to the table. The optional TableColumnModel and ListSelectionModel arguments let you specify the table column model and the row selection model. As an alternative to specifying a table model, you can supply data and column names, using arrays or vectors. Another option is to specify no data, optionally specifying the number of rows and columns (both integers) to be in the table.
void setPreferredScrollableViewportSize(Dimension)	Set the size of the visible part of the table when it's viewed within a scroll pane.
JTableHeader getTableHeader()	Get the component that displays the column names.

Manipulating Columns

Constructor or Method	Purpose
TableColumnModel getColumnModel() (in JTable)	Get the table's column model.
TableColumn getColumn(int) Enumeration getColumns() (in TableColumnModel)	Get one or all of the TableColumn objects for the table.
void setMinWidth(int) void setPreferredWidth(int) void setMaxWidth(int) (in TableColumn)	Set the minimum, preferred, or maximum width of the column.
int getMinWidth() int getPreferredWidth() int getMaxWidth() int getWidth() (in TableColumn)	Get the minimum, preferred, maximum, or current width of the column.

Using Editors and Renderers

Method	Purpose
void setDefaultRenderer(Class, TableCellRenderer) void setDefaultEditor(Class, TableCellEditor) (in JTable)	Set the renderer or editor used, by default, for all cells in all columns that return objects of the specified type.
void setCellRenderer(TableCellRenderer) void setCellEditor(TableCellEditor) (in TableColumn)	Set the renderer or editor used for all cells in this column.
TableCellRenderer getHeaderRenderer() (in TableColumn)	Get the header renderer for this column. Version Note:  As of 1.3, this method returns null if the column uses the default renderer. You generally use the TableHeader method getDefaultRenderer instead.
TableCellRenderer getDefaultRenderer() (in JTableHeader)	Get the header renderer used when none is defined by a table column. Introduced in 1.3.

Implementing Selection

Method	Purpose
void setSelectionMode(int)	Set the selection intervals allowed in the table. Valid values are defined in ListSelectionModel as SINGLE_SELECTION, SINGLE_INTERVAL_SELECTION, and MULTIPLE_INTERVAL_SELECTION (the default).
void setSelectionModel(ListSelectionModel) ListSelectionModel getSelectionModel()	Set or get the model used to control row selections.
void setRowSelectionAllowed(boolean) void setColumnSelectionAllowed(boolean) void setCellSelectionEnabled(boolean)	Set the table's selection orientation. The boolean argument specifies whether that particular type of selection is allowed. By default, row selection is allowed, and column and cell selection are not.

Examples that Use Tables

This table lists examples that use JTable and where those examples are described.

Example	Where Described	Notes
SimpleTableDemo	Creating a Simple Table	A basic table with no custom model. Does not include code to specify column widths or detect user editing.
SimpleTable- SelectionDemo	Detecting User Selections	Adds single selection and selection detection to SimpleTableDemo. By modifying the program's ALLOW_COLUMN_SELECTION and ALLOW_ROW_SELECTION constants, you can experiment with alternatives to the table default of allowing only rows to be selected.
TableDemo	Creating a Table Model	A basic table with a custom model.
TableFTFEditDemo	Using an Editor to Validate User-Entered Text	Modifies TableDemo to use a custom editor (a formatted text field variant) for all Integer data.
TableRenderDemo	Using a Combo Box as an Editor	Modifies TableDemo to use a custom editor (a combo box) for all data in the Sport column. Also intelligently picks column sizes. Uses renderers to display tool tips for the sport cells.
TableDialogEditDemo	Using Other Editors	Modifies TableDemo to have a cell renderer and editor that display a color and let you choose a new one, using a color chooser dialog.
TableToolTipsDemo	Specifying Tool Tips for Cells, Specifying Tool Tips for Column Headers,	Demonstrates how to use several techniques to set tool tip text for cells and column headers.
TableSorterDemo	Sorting and Otherwise Manipulating Data	Sorts column data by interposing a data manipulating table model between the data model and the table. Detects user clicks on column headers.
ListSelectionDemo	How to Write a List Selection Listener	Shows how to use all list selection modes, using a list selection listener that's shared between a table and list.
SharedModelDemo	Nowhere	Builds on ListSelectionDemo making the data model be shared between the table and list. If you edit an item in the first column of the table, the new value is reflected in the list.
TreeTable, TreeTable II	Creating TreeTables in Swing, Creating TreeTables: Part 2	Examples that combine a tree and table to show detailed information about a hierarchy such as a file system. The tree is a renderer for the table.

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