On Thu, 13 Jan 2022 08:25:22 GMT, Andrey Turbanov <d...@openjdk.java.net> wrote:
> Method `Class.isAssignableFrom` is often used in form of:
>
> if (clazz.isAssignableFrom(obj.getClass())) {
> Such condition could be simplified to more shorter and performarnt code
>
> if (clazz.isInstance(obj)) {
>
> Replacement is equivalent if it's known that `obj != null`.
> In JDK codebase there are many such places.
>
> I tried to measure performance via JMH
>
> Class<?> integerClass = Integer.class;
> Class<?> numberClass = Number.class;
>
> Object integerObject = 45666;
> Object doubleObject = 8777d;
>
> @Benchmark
> public boolean integerInteger_isInstance() {
> return integerClass.isInstance(integerObject);
> }
>
> @Benchmark
> public boolean integerInteger_isAssignableFrom() {
> return integerClass.isAssignableFrom(integerObject.getClass());
> }
>
> @Benchmark
> public boolean integerDouble_isInstance() {
> return integerClass.isInstance(doubleObject);
> }
>
> @Benchmark
> public boolean integerDouble_isAssignableFrom() {
> return integerClass.isAssignableFrom(doubleObject.getClass());
> }
>
> @Benchmark
> public boolean numberDouble_isInstance() {
> return numberClass.isInstance(doubleObject);
> }
>
> @Benchmark
> public boolean numberDouble_isAssignableFrom() {
> return numberClass.isAssignableFrom(doubleObject.getClass());
> }
>
> @Benchmark
> public boolean numberInteger_isInstance() {
> return numberClass.isInstance(integerObject);
> }
>
> @Benchmark
> public boolean numberInteger_isAssignableFrom() {
> return numberClass.isAssignableFrom(integerObject.getClass());
> }
>
> @Benchmark
> public void numberIntegerDouble_isInstance(Blackhole bh) {
> bh.consume(numberClass.isInstance(integerObject));
> bh.consume(numberClass.isInstance(doubleObject));
> }
>
> @Benchmark
> public void integerIntegerDouble_isAssignableFrom(Blackhole bh) {
> bh.consume(integerClass.isAssignableFrom(integerObject.getClass()));
> bh.consume(integerClass.isAssignableFrom(doubleObject.getClass()));
> }
>
> `isInstance` is a bit faster than `isAssignableFrom`
>
> Benchmark Mode Cnt Score Error Units
> integerDouble_isAssignableFrom avgt 5 1,173 ± 0,026 ns/op
> integerDouble_isInstance avgt 5 0,939 ± 0,038 ns/op
> integerIntegerDouble_isAssignableFrom avgt 5 2,106 ± 0,068 ns/op
> numberIntegerDouble_isInstance avgt 5 1,516 ± 0,046 ns/op
> integerInteger_isAssignableFrom avgt 5 1,175 ± 0,029 ns/op
> integerInteger_isInstance avgt 5 0,886 ± 0,017 ns/op
> numberDouble_isAssignableFrom avgt 5 1,172 ± 0,007 ns/op
> numberDouble_isInstance avgt 5 0,891 ± 0,030 ns/op
> numberInteger_isAssignableFrom avgt 5 1,169 ± 0,014 ns/op
> numberInteger_isInstance avgt 5 0,887 ± 0,016 ns/op
src/jdk.jfr/share/classes/jdk/jfr/internal/TypeLibrary.java line 405:
> 403: Object res = m.invoke(a, new Object[0]);
> 404: if (res instanceof Annotation[]) {
> 405: for (Annotation rep : (Annotation[])
> m.invoke(a, new Object[0])) {
BTW it looks suspicious to have `m.invoke(a, new Object[0])` called again here.
Shouldn't it just reuse `res` variable instead?
-------------
PR: https://git.openjdk.java.net/jdk/pull/7061
