RFR JDK-8011200 (was 7143928) : (coll) Optimize for Empty ArrayList and HashMap

[Martin Buchholz]

Style: spaces around "="

+    private static final int DEFAULT_CAPACITY= 10;

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It's a matter of taste whether to remove the temp var oldCapacity.  I
believe it was coded intentionally.

     public void trimToSize() {
         modCount++;
-        int oldCapacity = elementData.length;
-        if (size < oldCapacity) {
+        if (size < elementData.length) {
             elementData = Arrays.copyOf(elementData, size);
         }

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 754         throws java.io.IOException, ClassNotFoundException { 755
        elementData = EMPTY_ELEMENTDATA;


Your indentation is off.

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Because "threshold" is a serialized field, its javadoc is part of the
public interface of this class, and hence cannot refer to implementation
details like EMPTY_TABLE.

 161     /** 162      * The next size value at which to resize
(capacity * load factor). If 163      * table == EMPTY_TABLE then this
is the initial capacity at which the 164      * table will be created
when inflated.
 165      * @serial
 166      */
 167     int threshold;**

*
http://docs.oracle.com/javase/7/docs/api/serialized-form.html#java.util.HashMap
*
*
*

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Consider making roundUpToPowerOf2 public.

Best Implementation is not obvious.  I would probably write a loop with core
x = x & (x - 1)
until get to zero.

 274     private static int roundUpToPowerOf2(int number) { 275
 int rounded = number >= MAXIMUM_CAPACITY 276                 ?
MAXIMUM_CAPACITY 277                 : (rounded =
Integer.highestOneBit(number)) != 0 278                     ?
(Integer.bitCount(number) > 1) ? rounded << 1 : rounded 279
         : 1; 280  281         return rounded; 282     }



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I think it's a mistake to "optimize" for the empty case in code like this:

 694     public boolean containsValue(Object value) { 695         if
(isEmpty()) { 696             return false; 697         } 698