The performance impact of using instanceof in Java

Approach

I wrote a benchmark program to evaluate different implementations:

1. instanceof implementation (as reference)
2. object-orientated via an abstract class and @Override a test method
3. using an own type implementation
4. getClass() == _.class implementation

I used jmh to run the benchmark with 100 warmup calls, 1000 iterations under measuring, and with 10 forks. So each option was measured with 10 000 times, which takes 12:18:57 to run the whole benchmark on my MacBook Pro with macOS 10.12.4 and Java 1.8. The benchmark measures the average time of each option. For more details see my implementation on GitHub.

For the sake of completeness: There is a previous version of this answer and my benchmark.

Results

| Operation  | Runtime in nanoseconds per operation | Relative to instanceof |
|------------|--------------------------------------|------------------------|
| INSTANCEOF | 39,598 ± 0,022 ns/op                 | 100,00 %               |
| GETCLASS   | 39,687 ± 0,021 ns/op                 | 100,22 %               |
| TYPE       | 46,295 ± 0,026 ns/op                 | 116,91 %               |
| OO         | 48,078 ± 0,026 ns/op                 | 121,42 %               |

tl;dr

In Java 1.8 instanceof is the fastest approach, although getClass() is very close.

Modern JVM/JIT compilers have removed the performance hit of most of the traditionally "slow" operations, including instanceof, exception handling, reflection, etc.

As Donald Knuth wrote, "We should forget about small efficiencies, say about 97% of the time: premature optimization is the root of all evil." The performance of instanceof probably won't be an issue, so don't waste your time coming up with exotic workarounds until you're sure that's the problem.

I just made a simple test to see how instanceOf performance is comparing to a simple s.equals() call to a string object with only one letter.

in a 10.000.000 loop the instanceOf gave me 63-96ms, and the string equals gave me 106-230ms

I used java jvm 6.

So in my simple test is faster to do a instanceOf instead of a one character string comparison.

using Integer's .equals() instead of string's gave me the same result, only when I used the == i was faster than instanceOf by 20ms (in a 10.000.000 loop)