java.version=17.0.12 vm=Java HotSpot(TM) 64-Bit Server VM

== 1. volatile is visibility, not atomicity ==
plain int, two threads       final=1
volatile int, two threads    final=1
AtomicInteger CAS loop       final=2

== 2. volatile safe publication ==
reader sees value=42

== 3. ABA ==
AtomicInteger: expected=0 cas=true final=2
AtomicStampedReference: expected=0/0 cas=false final=0/2

== 4. ConcurrentHashMap lazy init and resize ==
new CHM<>()        table=0     sizeCtl=0     size=0
after put 1        table=16    sizeCtl=12    size=1
after put 13       table=32    sizeCtl=24    size=13
size=13 mappingCount=13
new CHM<>(1000)    table=0     sizeCtl=2048  size=0
after first put    table=2048  sizeCtl=1536  size=1

== 5. ConcurrentHashMap atomic merge ==
merge total=80000 expected=80000
0=20000 1=20000 2=20000 3=20000

== 6. ConcurrentHashMap rejects null ==
null key -> NullPointerException
null value -> NullPointerException
size=0