diff --git a/JSONArray.java b/JSONArray.java
index 54d5183..a402d67 100644
--- a/JSONArray.java
+++ b/JSONArray.java
@@ -154,8 +154,10 @@ public class JSONArray implements Iterable<Object> {
      *            A Collection.
      */
     public JSONArray(Collection<?> collection) {
-        this.myArrayList = new ArrayList<Object>();
-        if (collection != null) {
+        if (collection == null) {
+            this.myArrayList = new ArrayList<Object>();
+        } else {
+            this.myArrayList = new ArrayList<Object>(collection.size());
         	for (Object o: collection){
         		this.myArrayList.add(JSONObject.wrap(o));
         	}
@@ -172,6 +174,7 @@ public class JSONArray implements Iterable<Object> {
         this();
         if (array.getClass().isArray()) {
             int length = Array.getLength(array);
+            this.myArrayList.ensureCapacity(length);
             for (int i = 0; i < length; i += 1) {
                 this.put(JSONObject.wrap(Array.get(array, i)));
             }
@@ -495,7 +498,7 @@ public class JSONArray implements Iterable<Object> {
      * Get the optional object value associated with an index.
      *
      * @param index
-     *            The index must be between 0 and length() - 1.
+     *            The index must be between 0 and length() - 1. If not, null is returned.
      * @return An object value, or null if there is no object at that index.
      */
     public Object opt(int index) {
@@ -1150,7 +1153,13 @@ public class JSONArray implements Iterable<Object> {
         }
         if (index < this.length()) {
             this.myArrayList.set(index, value);
+        } else if(index == this.length()){
+            // simple append
+            this.put(value);
         } else {
+            // if we are inserting past the length, we want to grow the array all at once
+            // instead of incrementally.
+            this.myArrayList.ensureCapacity(index + 1);
             while (index != this.length()) {
                 this.put(JSONObject.NULL);
             }
@@ -1302,7 +1311,7 @@ public class JSONArray implements Iterable<Object> {
         if (names == null || names.length() == 0 || this.length() == 0) {
             return null;
         }
-        JSONObject jo = new JSONObject();
+        JSONObject jo = new JSONObject(names.length());
         for (int i = 0; i < names.length(); i += 1) {
             jo.put(names.getString(i), this.opt(i));
         }
diff --git a/JSONObject.java b/JSONObject.java
index 060a196..8ad7864 100644
--- a/JSONObject.java
+++ b/JSONObject.java
@@ -184,7 +184,7 @@ public class JSONObject {
      *            An array of strings.
      */
     public JSONObject(JSONObject jo, String[] names) {
-        this();
+        this(names.length);
         for (int i = 0; i < names.length; i += 1) {
             try {
                 this.putOnce(names[i], jo.opt(names[i]));
@@ -256,8 +256,10 @@ public class JSONObject {
      *            the JSONObject.
      */
     public JSONObject(Map<?, ?> m) {
-        this.map = new HashMap<String, Object>();
-        if (m != null) {
+        if (m == null) {
+            this.map = new HashMap<String, Object>();
+        } else {
+            this.map = new HashMap<String, Object>(m.size());
         	for (final Entry<?, ?> e : m.entrySet()) {
                 final Object value = e.getValue();
                 if (value != null) {
@@ -308,7 +310,7 @@ public class JSONObject {
      *            from the object.
      */
     public JSONObject(Object object, String names[]) {
-        this();
+        this(names.length);
         Class<?> c = object.getClass();
         for (int i = 0; i < names.length; i += 1) {
             String name = names[i];
@@ -377,6 +379,17 @@ public class JSONObject {
             }
         }
     }
+    
+    /**
+     * Constructor to specify an initial capacity of the internal map. Useful for library 
+     * internal calls where we know, or at least can best guess, how big this JSONObject
+     * will be.
+     * 
+     * @param initialCapacity initial capacity of the internal map.
+     */
+    protected JSONObject(int initialCapacity){
+        this.map = new HashMap<String, Object>(initialCapacity);
+    }
 
     /**
      * Accumulate values under a key. It is similar to the put method except
diff --git a/Property.java b/Property.java
index 4f1d7c4..51b97ed 100644
--- a/Property.java
+++ b/Property.java
@@ -41,7 +41,7 @@ public class Property {
      * @throws JSONException
      */
     public static JSONObject toJSONObject(java.util.Properties properties) throws JSONException {
-        JSONObject jo = new JSONObject();
+        JSONObject jo = new JSONObject(properties == null ? 0 : properties.size());
         if (properties != null && !properties.isEmpty()) {
             Enumeration<?> enumProperties = properties.propertyNames();
             while(enumProperties.hasMoreElements()) {