One trick that OpenJDK uses is optimization of null checks. Since in Java memory has to be initialized, null pointers will have the value 0. If a given function using a null check gets called many times, and all these times it was called with a non-null object the JVM can compile the branch totally away. If the function is finally called with ‘null’ the compiled code will try to load the memory at address zero, causing the TLB to trigger and the OS to send a segfault. This can be handled safely by the JVM which will interpret it in accordance with the above and will deoptimize the code (with all possible side effects reverted) and either run it in interpreted mode or an optimized mode that does contain the null check “properly”.