Reduce heap size of org.openstreetmap.josm.data.osm.Node by 8 bytes

[simon04]

We can save 8 bytes for each org.openstreetmap.josm.data.osm.Node instance by moving the mappaintCacheIdx from OsmPrimitive to AbstractPrimitive due to Java's memory layout alignment.

BEFORE org.openstreetmap.josm.data.osm.Node object internals:
 OFFSET  SIZE         TYPE DESCRIPTION                               VALUE
      0    16              (object header)                           N/A
     16     8         long AbstractPrimitive.id                      N/A
     24     4          int AbstractPrimitive.version                 N/A
     28     4          int AbstractPrimitive.changesetId             N/A
     32     4          int AbstractPrimitive.timestamp               N/A
     36     2        short AbstractPrimitive.flags                   N/A
     38     2              (alignment/padding gap)                  
     40     8         User AbstractPrimitive.user                    N/A
     48     8     String[] AbstractPrimitive.keys                    N/A
     56     2        short OsmPrimitive.mappaintCacheIdx             N/A
     58     6              (alignment/padding gap)                  
     64     8   StyleCache OsmPrimitive.mappaintStyle                N/A
     72     8      DataSet OsmPrimitive.dataSet                      N/A
     80     8       Object OsmPrimitive.referrers                    N/A
     88     8       double Node.lat                                  N/A
     96     8       double Node.lon                                  N/A
    104     8       double Node.east                                 N/A
    112     8       double Node.north                                N/A
    120     8       Object Node.eastNorthCacheKey                    N/A
Instance size: 128 bytes
Space losses: 8 bytes internal + 0 bytes external = 8 bytes total

src/org/openstreetmap/josm/data/osm/AbstractPrimitive.java

@@ -135 +135 @@
      */
     protected volatile short flags = FLAG_VISIBLE;   // visible per default
 
+    /**
+     * The mappaint cache index for this primitive.
+     * This field belongs to {@code OsmPrimitive}, but due to Java's memory layout alignment
+     */
+    protected short mappaintCacheIdx;
+
     /*-------------------
      * OTHER PROPERTIES
      *-------------------*/

src/org/openstreetmap/josm/data/osm/OsmPrimitive.java

@@ -145 +145 @@
      * MAPPAINT
      *--------*/
     private StyleCache mappaintStyle;
-    private short mappaintCacheIdx;
 
     @Override
     public final StyleCache getCachedStyle() {

AFTER org.openstreetmap.josm.data.osm.Node object internals:
 OFFSET  SIZE         TYPE DESCRIPTION                               VALUE
      0    16              (object header)                           N/A
     16     8         long AbstractPrimitive.id                      N/A
     24     4          int AbstractPrimitive.version                 N/A
     28     4          int AbstractPrimitive.changesetId             N/A
     32     4          int AbstractPrimitive.timestamp               N/A
     36     2        short AbstractPrimitive.flags                   N/A
     38     2        short AbstractPrimitive.mappaintCacheIdx        N/A
     40     8         User AbstractPrimitive.user                    N/A
     48     8     String[] AbstractPrimitive.keys                    N/A
     56     8   StyleCache OsmPrimitive.mappaintStyle                N/A
     64     8      DataSet OsmPrimitive.dataSet                      N/A
     72     8       Object OsmPrimitive.referrers                    N/A
     80     8       double Node.lat                                  N/A
     88     8       double Node.lon                                  N/A
     96     8       double Node.east                                 N/A
    104     8       double Node.north                                N/A
    112     8       Object Node.eastNorthCacheKey                    N/A
Instance size: 120 bytes
Space losses: 0 bytes internal + 0 bytes external = 0 bytes total

[simon04]

In 17849/josm:

fix #20830 - Reduce heap size of org.openstreetmap.josm.data.osm.Node by 8 bytes