The calls are intercepted and processed only when it can be unequivocally determined that the parameters can be reduced to a constant.įor example, the call Class.forName(String) will be replaced with a Class literal only if the String argument can be constant folded, assuming that the class is actually on the classpath.Īdditionally, a call to Class.getMethod(String, Class) will be processed only if the contents of the Class argument can be determined with certainty.
Java reflection example program code#
Second, GraalVM can employ constant folding and optimize the code further. If the target elements cannot be resolved, e.g., a class is not on the classpath or it does not declare a field/method/constructor, then the calls are replaced with a snippet that throws the appropriate exception at run time.įirst, at run time there are no calls to the Reflection API. If the target elements can be resolved, the calls are removed and instead the target elements are embedded in the code. If the arguments to these calls can be reduced to a constant, Native Image tries to resolve the target elements. The analysis intercepts calls to Class.forName(String), Class.forName(String, ClassLoader), Class.getDeclaredField(String), Class.getField(String), Class.getDeclaredMethod(String, Class), Class.getMethod(String, Class), Class.getDeclaredConstructor(Class), and Class.getConstructor(Class). See also the guide on assisted configuration of Java resources and other dynamic features.
Java reflection example program manual#
Where the analysis fails, the program elements reflectively accessed at run time must be specified using a manual configuration. Native Image tries to resolve the target elements through a static analysis that detects calls to the Reflection API. (Note: loading classes with Class.forName(String) are included here since it is closely related to reflection.) Native Image has partial support for reflection and needs to know ahead-of-time the reflectively accessed program elements.Įxamining and accessing program elements through .* or loading classes with Class.forName(String) at run time requires preparing additional metadata for those program elements. Java reflection support (the .* API) enables Java code to examine its own classes, methods, fields and their properties at run time.
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