diff --git a/modules/javafx.controls/src/main/java/com/sun/javafx/scene/control/ReadOnlyUnbackedObservableList.java b/modules/javafx.controls/src/main/java/com/sun/javafx/scene/control/ReadOnlyUnbackedObservableList.java
index 0e2d4451ea..a4ea0cf4c7 100644
--- a/modules/javafx.controls/src/main/java/com/sun/javafx/scene/control/ReadOnlyUnbackedObservableList.java
+++ b/modules/javafx.controls/src/main/java/com/sun/javafx/scene/control/ReadOnlyUnbackedObservableList.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2010, 2017, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2010, 2020, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -113,7 +113,7 @@ public void callObservers(Change<E> c) {
     @Override public int indexOf(Object o) {
         if (o == null) return -1;
 
-        for (int i = 0; i < size(); i++) {
+        for (int i = 0, max = size(); i < max; i++) {
             Object obj = get(i);
             if (o.equals(obj)) return i;
         }
@@ -185,8 +185,9 @@ public void callObservers(Change<E> c) {
 
     @Override
     public Object[] toArray() {
-        Object[] arr = new Object[size()];
-        for (int i = 0; i < size(); i++) {
+        int max = size();
+        Object[] arr = new Object[max];
+        for (int i = 0; i < max; i++) {
             arr[i] = get(i);
         }
         return arr;
diff --git a/modules/javafx.controls/src/main/java/javafx/scene/control/MultipleSelectionModelBase.java b/modules/javafx.controls/src/main/java/javafx/scene/control/MultipleSelectionModelBase.java
index d8c29e7ef3..52eb7ea560 100644
--- a/modules/javafx.controls/src/main/java/javafx/scene/control/MultipleSelectionModelBase.java
+++ b/modules/javafx.controls/src/main/java/javafx/scene/control/MultipleSelectionModelBase.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2010, 2018, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2010, 2020, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -626,6 +626,7 @@ private void quietClearSelection() {
     class SelectedIndicesList extends ReadOnlyUnbackedObservableList<Integer> {
         private final BitSet bitset;
 
+        private int size = -1;
         private int lastGetIndex = -1;
         private int lastGetValue = -1;
 
@@ -694,6 +695,7 @@ public void set(int index) {
             }
 
             _beginChange();
+            size = -1;
             bitset.set(index);
             int indicesIndex = indexOf(index);
             _nextAdd(indicesIndex, indicesIndex + 1);
@@ -714,6 +716,7 @@ public void set(int index, boolean isSet) {
 
         public void set(int index, int end, boolean isSet) {
             _beginChange();
+            size = -1;
             if (isSet) {
                 bitset.set(index, end, isSet);
                 int indicesIndex = indexOf(index);
@@ -791,6 +794,7 @@ public void set(int index, int... indices) {
         public void clear() {
             _beginChange();
             List<Integer> removed = bitset.stream().boxed().collect(Collectors.toList());
+            size = 0;
             bitset.clear();
             _nextRemove(0, removed);
             _endChange();
@@ -800,6 +804,7 @@ public void clear(int index) {
             if (!bitset.get(index)) return;
 
             _beginChange();
+            size = -1;
             bitset.clear(index);
             _nextRemove(index, index);
             _endChange();
@@ -855,7 +860,11 @@ public boolean isNotSelected(int index) {
 
         /** Returns number of true bits in BitSet */
         @Override public int size() {
-            return bitset.cardinality();
+            if (size >= 0) {
+                return size;
+            }
+            size = bitset.cardinality();
+            return size;
         }
 
         /** Returns the number of bits reserved in the BitSet */
@@ -864,8 +873,48 @@ public int bitsetSize() {
         }
 
         @Override public int indexOf(Object obj) {
-            reset();
-            return super.indexOf(obj);
+            if (!(obj instanceof Number)) {
+                return -1;
+            }
+            Number n = (Number) obj;
+            int index = n.intValue();
+            if (!bitset.get(index)) {
+                return -1;
+            }
+            // is left most bit
+            if (index == 0) {
+                return 0;
+            }
+
+            // is right most bit
+            if (index == bitset.length()-1) {
+                return size()-1;
+            }
+
+            // count right bit
+            if (index > bitset.length()/2) {
+                int count = 1;
+                for (;;) {
+                    index = bitset.nextSetBit(index + 1);
+                    if (index < 0) {
+                        break;
+                    }
+                    count++;
+                }
+                return size() - count;
+            }
+
+            // count left bit
+            // return (int)bitset.stream().takeWhile(i->i<index).count();
+            int count = 0;
+            for (;;) {
+                index = bitset.previousSetBit(index-1);
+                if (index < 0) {
+                    break;
+                }
+                count++;
+            }
+            return count;
         }
 
         @Override public boolean contains(Object o) {