15.4 Selecting Table Entries

All this, and all we can do is render and edit data in a table. "What about selecting data?" you ask. Yes, we can do that, too. And, as you might expect, the ListSelectionModel (discussed in Chapter 7) drives us through these selections. Unlike most of the other components, however, the two-dimensional JTable has two selection models, one for rows and one for columns.

Figure 15-8 shows an application that allows you to turn on and off the various selections allowed on a table (cell, row, and column). As you select different rows and columns, two status labels show you the indices of the selected items.

Figure 15-8. A table that lets you select rows, columns, or cells

Let's look at the code for this example. Most of the work is getting the interface you see running. Once that's done, we attach our two reporting labels as listeners to the row selection and column selection models. The interesting part of the code is the ListSelectionListener, written as an inner class. This class tracks any ListSelectionModel and updates a label with the currently selected indices every time it changes. (Those indices are retrieved using the getSelectedIndices( ) method we wrote ourselves.) Since we rely on only the list selection model, we can use the same event handler for both the row and the column selections.

// SelectionExample.java // A simple multiplication table with the ability to play with row and column // selections. You can alter the cell, column, and row selection properties // of the table at runtime. // import java.awt.*; import java.awt.event.*; import javax.swing.*; import javax.swing.event.*; import javax.swing.table.*; public class SelectionExample extends JFrame {   public SelectionExample( ) {     super("Selection Model Test");     setSize(450, 350);     setDefaultCloseOperation(EXIT_ON_CLOSE);     TableModel tm = new AbstractTableModel( ) {       // We'll create a simple multiplication table to serve as a noneditable       // table with several rows and columns.       public int getRowCount( ) { return 10; }       public int getColumnCount( ) { return 10; }       public Object getValueAt(int r, int c) { return "" + (r+1)*(c+1); }     };     final JTable jt = new JTable(tm);     JScrollPane jsp = new JScrollPane(jt);     getContentPane( ).add(jsp, BorderLayout.CENTER);     // Now set up our selection controls.     JPanel controlPanel, buttonPanel, columnPanel, rowPanel;          buttonPanel = new JPanel( );     final JCheckBox cellBox, columnBox, rowBox;     cellBox = new JCheckBox("Cells", jt.getCellSelectionEnabled( ));     columnBox = new JCheckBox("Columns", jt.getColumnSelectionAllowed( ));     rowBox = new JCheckBox("Rows", jt.getRowSelectionAllowed( ));     cellBox.addActionListener(new ActionListener( ) {       public void actionPerformed(ActionEvent ae) {         jt.setCellSelectionEnabled(cellBox.isSelected( ));         columnBox.setSelected(jt.getColumnSelectionAllowed( ));         rowBox.setSelected(jt.getRowSelectionAllowed( ));       }     } );     columnBox.addActionListener(new ActionListener( ) {       public void actionPerformed(ActionEvent ae) {         jt.setColumnSelectionAllowed(columnBox.isSelected( )); cellBox.setSelected(jt.getCellSelectionEnabled( ));       }     } );     rowBox.addActionListener(new ActionListener( ) {       public void actionPerformed(ActionEvent ae) {         jt.setRowSelectionAllowed(rowBox.isSelected( )); cellBox.setSelected(jt.getCellSelectionEnabled( ));       }     } );     buttonPanel.add(new JLabel("Selections allowed:"));     buttonPanel.add(cellBox);     buttonPanel.add(columnBox);     buttonPanel.add(rowBox);     columnPanel = new JPanel( );     ListSelectionModel csm = jt.getColumnModel( ).getSelectionModel( );     JLabel columnCounter = new JLabel("(Selected Column Indices Go Here)");     csm.addListSelectionListener(new SelectionDebugger(columnCounter, csm));     columnPanel.add(new JLabel("Selected columns:"));     columnPanel.add(columnCounter);     rowPanel = new JPanel( );     ListSelectionModel rsm = jt.getSelectionModel( );     JLabel rowCounter = new JLabel("(Selected Row Indices Go Here)");     rsm.addListSelectionListener(new SelectionDebugger(rowCounter, rsm));     rowPanel.add(new JLabel("Selected rows:"));     rowPanel.add(rowCounter);     controlPanel = new JPanel(new GridLayout(0, 1));     controlPanel.add(buttonPanel);     controlPanel.add(columnPanel);     controlPanel.add(rowPanel);     getContentPane( ).add(controlPanel, BorderLayout.SOUTH);   }   public static void main(String args[]) {     SelectionExample se = new SelectionExample( );     se.setVisible(true);   }      public class SelectionDebugger implements ListSelectionListener {     JLabel debugger;     ListSelectionModel model;     public SelectionDebugger(JLabel target, ListSelectionModel lsm) {       debugger = target;       model = lsm;     }     public void valueChanged(ListSelectionEvent lse) {       if (!lse.getValueIsAdjusting( )) {         // Skip all the intermediate events.         StringBuffer buf = new StringBuffer( );         int[] selection = getSelectedIndices(model.getMinSelectionIndex( ),                                              model.getMaxSelectionIndex( ));         if (selection.length == 0) {           buf.append("none");         }         else {           for (int i = 0; i < selection.length -1; i++) {             buf.append(selection[i]);             buf.append(", ");           }           buf.append(selection[selection.length - 1]);         }         debugger.setText(buf.toString( ));       }     }     // This method returns an array of selected indices. It's guaranteed to     // return a non-null value.     protected int[] getSelectedIndices(int start, int stop) {       if ((start == -1) || (stop == -1)) {         // No selection, so return an empty array         return new int[0];       }       int guesses[] = new int[stop - start + 1];       int index = 0;       // Manually walk through these.       for (int i = start; i <= stop; i++) {         if (model.isSelectedIndex(i)) {           guesses[index++] = i;         }       }              // Pare down the guess array to the real thing.       int realthing[] = new int[index];       System.arraycopy(guesses, 0, realthing, 0, index);       return realthing;     }   } }

It is definitely worth pointing out that for this specific application we could have retrieved the array of selected row indices from the JTable object and the array of selected column indices from the table's column model. Those classes have methods similar to our getSelectedIndices( ) method. However, that would have required two separate handlers. But quite honestly, outside this example, two separate handlers might be easier to write and maintain.