See email discussion: http://mail.openjdk.java.net/pipermail/hotspot-runtime-dev/2017-May/023453.html

Summary of problem:

If we create bytecode that does a "new" but which then fails to call invokespecial with a constructor, and uses that "reference" for a monitorenter or monitorexit, the hotspot verifier does not complain. In constrast IBM's J9 fails verification with:

Exception in thread "main" java.lang.VerifyError: JVMVRFY012 stack shape
inconsistent; class=Search, method=main([Ljava/lang/String;)V, pc=6
Exception Details:
  Location:
    Search.main([Ljava/lang/String;)V @6: JBmonitorenter
  Reason:
    Type 'uninitialized' (current frame, stack[1]) is not assignable to
'java/lang/Object'
  Current Frame:
    bci: @6
    flags: { }
    locals: { 'Search', '[Ljava/lang/String;' }
    stack: { 'uninitialized', 'uninitialized' }
at T.main(T.java:4)