I have had my 64-bit PC since 2013, about which I keep a log of all events. Several notes mention installing 32-bit Java. I believe I misunderstood the instructions that recommended it should be installed on 64-bit machines under certain circumstances. JOSM operated well, nevertheless, until a year ago, when I encountered the lack of memory issue first.
I uninstalled Java 8u191, downloaded its 64-bit equivalent and installed it. I am delighted to report everything has returned to normal.
I began using JOSM in 2008, following the purchase of my first GPSr. I sing its praises at every opportunity and continue to obtain great pleasure from using it.
I thank you for determining the solution to this setback. Hurrah! for mailing lists and forums.