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The Cost of Reflection on JVM Performance and Internal Access Checks
- Calling a method reflectively in Java involves multiple internal steps on the JVM, including method lookup, creation of Method object, bytecode generation, and access checks.
- Unlike direct method calls, reflective calls incur additional runtime work and checks, slowing down the process.
- Direct method calls benefit from JIT compiler optimizations like inlining, which reflective calls lack due to runtime method determination.
- Reflective calls involve argument conversion processes, boxing and unboxing of primitive types, leading to performance overhead.
- Reflection in Java allows accessing private state through setAccessible(true), bypassing normal access controls, which was widely used in frameworks.
- Java Platform Module System introduced boundaries for access control, requiring explicit declarations for reflective access, impacting frameworks relying on deep reflection.
- Introduction of modules shifted the access control paradigm, making reflective access dependent on module-level permissions rather than setAccessible(true) alone.
- Java deprecated the --illegal-access option, now enforcing access restrictions defined by module declarations, affecting reflection-heavy tools and frameworks.
- Frameworks adapted by using new alternatives like sun.misc.Unsafe or VarHandle when faced with restricted reflective access due to module boundaries.
- Reflection in Java continues to be used but with considerations for module-level boundaries and explicit permissions post-Java 9.
- Understanding the complexities of reflective access in the context of Java modules helps navigate the limitations and requirements imposed by the JVM.
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