This bug report is derived from this email to nashorn-dev alias: http://mail.openjdk.java.net/pipermail/nashorn-dev/2014-August/003345.html File: atomic.js x = new java.util.concurrent.atomic.AtomicInteger() x.incrementAndGet() print(x + '\n') function getAtomic() { return new java.util.concurrent.atomic.AtomicInteger() } x = getAtomic() x.incrementAndGet() print(x + '\n') Expected output: 1 1 Output seen with jdk8u20: 1 1 Output seen with jdk8u-dev and jdk9-dev: 1 atomic.js:10 TypeError: 0 has no such function "incrementAndGet" Output with --optimistic-types=false option: 1 1