[OpenJDK 2D-Dev] Patch submission: javadoc typos, javac warnings, AffineTransform.hashCode() and others
martin.desruisseaux at geomatys.fr
Wed Nov 9 12:49:15 PST 2011
This is my first post on this mailing list. To introduce myself, I'm a developer
of the open source GeoAPI (http://www.geoapi.org) and Geotoolkit.org
(http://www.geotoolkit.org) projects. We use Java2D for rendering maps, but also
Image I/O for raster data and we make extensive use of AffineTransform for
calculation purpose (as a step in a chain of operations performing map projections).
I published here a first set of proposed patches: http://webrev.geomatys.com/
I think most of them are minors. The most questionable one is probably the patch
for the AffineTransform equals/hashCode methods. The intend is to make
AffineTransform fully compliant with the contract described in
Object.equals(Object) and Object.hashCode() javadoc, in particular:
* Object.equals is reflexive: for any non-null reference value x, x.equals(x)
should return true.
* If two objects are equal according to the equals(Object) method, then
calling the hashCode method on each of the two objects must produce the same
The current AffineTransform implementation breaks those contracts in some
particular cases. The reflexivity contract is broken if at least one coefficient
is NaN. The hashCode() contract is broken if an affine transform contains
positive zeros while the other affine transform contains negative zeros.
In core JDK, java.lang.Double.equals(Object) does not use the == operation for
comparing floating point values, but instead uses doubleToLongBits(double). This
is probably the safest way to ensure strict compliance with Object contract.
However in order to preserve compatibility with the current AffineTransform
behavior at least for non-NaN values, the proposed patch uses a slightly
modified version of doubleToLongBits(double), which consider negative zero as
equals to positive zero. Note that the JDK doubleToLongBits(double) method
already collapses all NaN values into a canonical value, so the proposed patch
could be seen as an extension of the later where the two possible zero values
are also collapsed into a canonical one.
Note that negative zeros actually happens quite often on the translateY (m12)
coefficient with geospatial data, because the scaleY (m11) coefficient usually
have a negative value when the data to display have y ordinate values increasing
upward rather than downward.
The purpose of this patch is to make AffineTransform suitable for use as keys in
HashMap or as element in collections. In current implementation, an
AffineTransform added into a collection can never be removed by the
remove(Object) method if the collection implementation uses only the
equals(Object) method and the AffineTransform contains NaN values. Other methods
like contains(Object) have similar issues.
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