improve robustness of channel table

src/main/java/org/micromanager/lightsheetmanager/gui/tabs/AcquisitionTab.java

@@ -151,15 +151,13 @@ private void createUserInterface() {
         Button.setDefaultSize(140, 30);
         btnRunOverviewAcq_ = new Button("Overview Acquisition");
 
-        cbxUseChannels_ = new CheckBox(
-                "Channels", acqSettings.isUsingChannels());
+        final boolean isUsingChannels = acqSettings.isUsingChannels();
+        cbxUseChannels_ = new CheckBox("Channels", isUsingChannels);
         pnlChannelTable_ = new ChannelTablePanel(model_, cbxUseChannels_);
         pnlChannelTable_.setMaximumSize(new Dimension(270, 400));
 
         // disable elements based on acqSettings
-        if (!acqSettings.isUsingChannels()) {
-            pnlChannelTable_.setItemsEnabled(false);
-        }
+        pnlChannelTable_.setItemsEnabled(isUsingChannels);
 
         // acquisition mode combo box
         final boolean isUsingScanSettings = model_.devices().isUsingStageScanning();

src/main/java/org/micromanager/lightsheetmanager/gui/tabs/channels/ChannelTable.java

@@ -39,12 +39,11 @@ public ChannelTable(final LightSheetManager model) {
         table_ = new JTable(tableModel_);
 
         // init presets combo box
-        TableColumn column = table_.getColumnModel().getColumn(1);
         cmbPresets_ = new JComboBox<>();
-
-        // update presets
         updatePresetComboBoxes(channelGroup);
 
+        // set the editor
+        TableColumn column = table_.getColumnModel().getColumn(1);
         column.setCellEditor(new DefaultCellEditor(cmbPresets_));
 
         // cancel JTable edits when focus is lost to prevent errors

src/main/java/org/micromanager/lightsheetmanager/gui/tabs/channels/ChannelTableModel.java

@@ -8,6 +8,11 @@
 
 public class ChannelTableModel extends AbstractTableModel {
 
+    // column constants
+    private static final int COLUMN_USE = 0;
+    private static final int COLUMN_PRESET = 1;
+    private static final int COLUMN_OFFSET = 2;
+
     /**Column names for the channels table. */
     private final String[] columnNames_ = {
             "Use",
@@ -27,13 +32,23 @@ public int getRowCount() {
     }
 
     @Override
-    public Class<?> getColumnClass(int c) {
-        return getValueAt(0, c).getClass();
+    public int getColumnCount() {
+        return columnNames_.length;
     }
 
     @Override
-    public int getColumnCount() {
-        return columnNames_.length;
+    public Class<?> getColumnClass(int c) {
+        switch (c) {
+            case COLUMN_USE:
+                return Boolean.class;
+            case COLUMN_PRESET:
+                return String.class;
+            case COLUMN_OFFSET:
+                return Double.class;
+            default:
+                // Note: This will never happen if getColumnCount is correct.
+                throw new IllegalArgumentException("Invalid column index: " + c);
+        }
     }
 
     @Override
@@ -48,13 +63,13 @@ public boolean isCellEditable(int row, int col) {
 
     @Override
     public Object getValueAt(int row, int col) {
-        ChannelSpec channelSpec = tableData_.getChannelByIndex(row);
+       final ChannelSpec channelSpec = tableData_.getChannelByIndex(row);
         switch (col) {
-            case 0:
+            case COLUMN_USE:
                 return channelSpec.isUsed();
-            case 1:
+            case COLUMN_PRESET:
                 return channelSpec.getName();
-            case 2:
+            case COLUMN_OFFSET:
                 return channelSpec.getOffset();
             default:
                 throw new IllegalArgumentException("Invalid column index: " + col);
@@ -63,26 +78,34 @@ public Object getValueAt(int row, int col) {
 
     @Override
     public void setValueAt(Object value, int row, int col) {
-        ChannelSpec channelSpec = tableData_.getChannelByIndex(row);
+        final ChannelSpec channelSpec = tableData_.getChannelByIndex(row);
         switch (col) {
-            case 0:
+            case COLUMN_USE:
                 if (value instanceof Boolean) {
                     channelSpec.setUsed((boolean) value);
+                } else {
+                   return; // early exit => wrong type
                 }
                 break;
-            case 1:
+            case COLUMN_PRESET:
                 if (value instanceof String) {
                     channelSpec.setName((String) value);
+                } else {
+                   return; // early exit => wrong type
                 }
                 break;
-            case 2:
+            case COLUMN_OFFSET:
                 if (value instanceof Double) {
                     channelSpec.setOffset((double) value);
+                } else {
+                   return; // early exit => wrong type
                 }
                 break;
             default:
                 throw new IllegalArgumentException("Invalid column index: " + col);
         }
+
+        // update the table ui
         fireTableCellUpdated(row, col);
     }