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Eclipse OpenJ9™ allows both positive and negative identity hashcodes (System.identityHashCode / Object.hashCode). This is problematic for programs that incorrectly assume hashcodes can only be positive.

When enabled, this option limits identity hash codes to non-negative values.

Because limiting identity hash codes to non-negative values can have an impact on the performance of hash-intensive operations, this option is not enabled by default.


Setting Effect Default
-XX:+PositiveIdentityHash Enable
-XX:-PositiveIdentityHash Disable yes