Added notifier interface and classes.

app/src/processing/app/helpers/BasicNotifier.java

@@ -0,0 +1,25 @@
+package processing.app.helpers;
+
+import static processing.app.I18n._;
+
+public class BasicNotifier implements UserNotifier {
+
+  public void showError(String title, String message, Throwable e) {
+    showError(title, message, e, 1);
+  }
+
+  /**
+   * Show an error message that's actually fatal to the program.
+   * This is an error that can't be recovered. Use showWarning()
+   * for errors that allow P5 to continue running.
+   */
+  public void showError(String title, String message, Throwable e, int exit_code) {
+    if (title == null) title = _("Error");
+
+    System.err.println(title + ": " + message);
+
+    if (e != null) e.printStackTrace();
+    System.exit(exit_code);
+  }
+
+}

app/src/processing/app/helpers/GUINotifier.java

@@ -0,0 +1,29 @@
+package processing.app.helpers;
+
+import static processing.app.I18n._;
+
+import java.awt.Frame;
+
+import javax.swing.JOptionPane;
+
+public class GUINotifier implements UserNotifier {
+
+  public void showError(String title, String message, Throwable e) {
+    showError(title, message, e, 1);
+  }
+
+  /**
+   * Show an error message that's actually fatal to the program.
+   * This is an error that can't be recovered. Use showWarning()
+   * for errors that allow P5 to continue running.
+   */
+  public void showError(String title, String message, Throwable e, int exit_code) {
+    if (title == null) title = _("Error");
+
+    JOptionPane.showMessageDialog(new Frame(), message, title,
+                                  JOptionPane.ERROR_MESSAGE);
+
+    if (e != null) e.printStackTrace();
+    System.exit(exit_code);
+  }
+}

app/src/processing/app/helpers/UserNotifier.java

@@ -0,0 +1,9 @@
+package processing.app.helpers;
+
+public interface UserNotifier {
+
+  public void showError(String title, String message, Throwable e);
+
+  public void showError(String title, String message, Throwable e, int exit_code);
+
+}