The cost is in loading the bounds (e.g. array size) from memory. If you access 100 different arrays, you get 100 load operations for the sizes. A register woul

The cost is in loading the bounds (e.g. array size) from memory. If you access 100 different arrays, you get 100 load operations for the sizes. A register would only help if you access the same array in a loop, but the majority of loops doesn't need repeated bounds checking anyway: list-map operations, list-reduce operations, System.arraycopy(), whatever -- these only have to check the bounds once before starting the loop. The JVM specifies that every array access gets checked, but since arrays can't change their size, the JIT compiler can move that check outside the loop.