Java 18 改进了 java.lang.reflect.Method、Constructor 的实现逻辑，使之性能更好，速度更快。这项改动不会改动相关 API ，这意味着开发中不需要改动反射相关代码，就可以体验到性能更好反射。
OpenJDK 官方给出了新老实现的反射性能基准测试结果。
Java 18 之前：
Benchmark Mode Cnt Score Error Units
ReflectionSpeedBenchmark.constructorConst avgt 10 68.049 ± 0.872 ns/op
ReflectionSpeedBenchmark.constructorPoly avgt 10 94.132 ± 1.805 ns/op
ReflectionSpeedBenchmark.constructorVar avgt 10 64.543 ± 0.799 ns/op
ReflectionSpeedBenchmark.instanceFieldConst avgt 10 35.361 ± 0.492 ns/op
ReflectionSpeedBenchmark.instanceFieldPoly avgt 10 67.089 ± 3.288 ns/op
ReflectionSpeedBenchmark.instanceFieldVar avgt 10 35.745 ± 0.554 ns/op
ReflectionSpeedBenchmark.instanceMethodConst avgt 10 77.925 ± 2.026 ns/op
ReflectionSpeedBenchmark.instanceMethodPoly avgt 10 96.094 ± 2.269 ns/op
ReflectionSpeedBenchmark.instanceMethodVar avgt 10 80.002 ± 4.267 ns/op
ReflectionSpeedBenchmark.staticFieldConst avgt 10 33.442 ± 2.659 ns/op
ReflectionSpeedBenchmark.staticFieldPoly avgt 10 51.918 ± 1.522 ns/op
ReflectionSpeedBenchmark.staticFieldVar avgt 10 33.967 ± 0.451 ns/op
ReflectionSpeedBenchmark.staticMethodConst avgt 10 75.380 ± 1.660 ns/op
ReflectionSpeedBenchmark.staticMethodPoly avgt 10 93.553 ± 1.037 ns/op
ReflectionSpeedBenchmark.staticMethodVar avgt 10 76.728 ± 1.614 ns/op
Java 18 的新实现：
Benchmark Mode Cnt Score Error Units
ReflectionSpeedBenchmark.constructorConst avgt 10 32.392 ± 0.473 ns/op
ReflectionSpeedBenchmark.constructorPoly avgt 10 113.947 ± 1.205 ns/op
ReflectionSpeedBenchmark.constructorVar avgt 10 76.885 ± 1.128 ns/op
ReflectionSpeedBenchmark.instanceFieldConst avgt 10 18.569 ± 0.161 ns/op
ReflectionSpeedBenchmark.instanceFieldPoly avgt 10 98.671 ± 2.015 ns/op
ReflectionSpeedBenchmark.instanceFieldVar avgt 10 54.193 ± 3.510 ns/op
ReflectionSpeedBenchmark.instanceMethodConst avgt 10 33.421 ± 0.406 ns/op
ReflectionSpeedBenchmark.instanceMethodPoly avgt 10 109.129 ± 1.959 ns/op
ReflectionSpeedBenchmark.instanceMethodVar avgt 10 90.420 ± 2.187 ns/op
ReflectionSpeedBenchmark.staticFieldConst avgt 10 19.080 ± 0.179 ns/op
ReflectionSpeedBenchmark.staticFieldPoly avgt 10 92.130 ± 2.729 ns/op
ReflectionSpeedBenchmark.staticFieldVar avgt 10 53.899 ± 1.051 ns/op
ReflectionSpeedBenchmark.staticMethodConst avgt 10 35.907 ± 0.456 ns/op
ReflectionSpeedBenchmark.staticMethodPoly avgt 10 102.895 ± 1.604 ns/op
ReflectionSpeedBenchmark.staticMethodVar avgt 10 82.123 ± 0.629 ns/op
可以看到在某些场景下性能稍微好些。