diff --git a/java/src/processing/mode/java/DebugTray.java b/java/src/processing/mode/java/DebugTray.java
index e322efd50..a48348444 100644
--- a/java/src/processing/mode/java/DebugTray.java
+++ b/java/src/processing/mode/java/DebugTray.java
@@ -80,6 +80,8 @@ public class DebugTray extends JFrame {
   /// processing / "advanced" mode flag (currently not used)
   protected boolean p5mode = true; 
 
+  // The tray will be placed at this amount from the top of the editor window,
+  // and extend to this amount from the bottom of the editor window.
   final int VERTICAL_OFFSET = 64;
     
   
diff --git a/java/src/processing/mode/java/debug/LineHighlight.java b/java/src/processing/mode/java/debug/LineHighlight.java
index 5320f1822..13ad3bfbc 100644
--- a/java/src/processing/mode/java/debug/LineHighlight.java
+++ b/java/src/processing/mode/java/debug/LineHighlight.java
@@ -33,7 +33,7 @@ import processing.mode.java.JavaEditor;
  *
  * @author Martin Leopold <m@martinleopold.com>
  */
-public class LineHighlight implements LineListener {
+public class LineHighlight {
 
   protected JavaEditor editor; // the view, used for highlighting lines by setting a background color
   protected Color bgColor; // the background color for highlighting lines
@@ -154,7 +154,6 @@ public class LineHighlight implements LineListener {
      * @param oldLineIdx the old line index (0-based)
      * @param newLineIdx the new line index (0-based)
      */
-    @Override
     public void lineChanged(LineID line, int oldLineIdx, int newLineIdx) {
         // clear old line
         if (editor.isInCurrentTab(new LineID(line.fileName(), oldLineIdx))) {
diff --git a/java/src/processing/mode/java/debug/LineID.java b/java/src/processing/mode/java/debug/LineID.java
index c66f716a2..96a0ff1f7 100644
--- a/java/src/processing/mode/java/debug/LineID.java
+++ b/java/src/processing/mode/java/debug/LineID.java
@@ -45,7 +45,7 @@ public class LineID implements DocumentListener {
     protected int lineIdx; // the line number, 0-based
     protected Document doc; // the Document to use for line number tracking
     protected Position pos; // the Position acquired during line number tracking
-    protected Set<LineListener> listeners = new HashSet<LineListener>(); // listeners for line number changes
+    protected Set<LineHighlight> listeners = new HashSet<LineHighlight>(); // listeners for line number changes
 
     public LineID(String fileName, int lineIdx) {
         this.fileName = fileName;
@@ -181,7 +181,7 @@ public class LineID implements DocumentListener {
             int oldLineIdx = lineIdx;
             lineIdx = doc.getDefaultRootElement().getElementIndex(offset); // offset to lineNo
             if (lineIdx != oldLineIdx) {
-                for (LineListener l : listeners) {
+                for (LineHighlight l : listeners) {
                     if (l != null) {
                         l.lineChanged(this, oldLineIdx, lineIdx);
                     } else {
@@ -197,7 +197,7 @@ public class LineID implements DocumentListener {
      *
      * @param l the listener to add
      */
-    public void addListener(LineListener l) {
+    public void addListener(LineHighlight l) {
         listeners.add(l);
     }
 
@@ -206,7 +206,7 @@ public class LineID implements DocumentListener {
      *
      * @param l the listener to remove
      */
-    public void removeListener(LineListener l) {
+    public void removeListener(LineHighlight l) {
         listeners.remove(l);
     }
 
diff --git a/java/src/processing/mode/java/debug/LineListener.java b/java/src/processing/mode/java/debug/LineListener.java
deleted file mode 100644
index 210965899..000000000
--- a/java/src/processing/mode/java/debug/LineListener.java
+++ /dev/null
@@ -1,38 +0,0 @@
-/* -*- mode: java; c-basic-offset: 2; indent-tabs-mode: nil -*- */
-
-/*
-Part of the Processing project - http://processing.org
-Copyright (c) 2012-15 The Processing Foundation
-
-This program is free software; you can redistribute it and/or modify
-it under the terms of the GNU General Public License version 2
-as published by the Free Software Foundation.
-
-This program is distributed in the hope that it will be useful,
-but WITHOUT ANY WARRANTY; without even the implied warranty of
-MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-GNU General Public License for more details.
-
-You should have received a copy of the GNU General Public License
-along with this program; if not, write to the Free Software Foundation, Inc.
-51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
-*/
-
-package processing.mode.java.debug;
-
-/**
- * A Listener for line number changes.
- *
- * @author Martin Leopold <m@martinleopold.com>
- */
-public interface LineListener {
-
-    /**
-     * Event handler for line number changes (due to editing).
-     *
-     * @param line the line that has changed
-     * @param oldLineIdx the old line index (0-based)
-     * @param newLineIdx the new line index (0-based)
-     */
-    void lineChanged(LineID line, int oldLineIdx, int newLineIdx);
-}
diff --git a/todo.txt b/todo.txt
index 566531afd..5997f8ef8 100644
--- a/todo.txt
+++ b/todo.txt
@@ -100,6 +100,8 @@ X     removed, seems to be duplicate/used the same way
 _ crashed on startup w/ JavaScript mode as default b/c PdeKeyListener not found
 _   because it's in the other ClassLoader, can no longer rely on it
 
+_ do the right thing on passing around List vs ArrayList and others
+
 gui
 _ need 'actively pressed' version of 'play' and 'stop'
 _   could do rollover as well, but do other apps use them?