Can Java Reflection Retrieve Method Parameter Names?

Java Reflection: Accessing Method Parameter Names

Question:

Can Java reflection provide information about method parameter names?

Answer:

Yes, Java 8 introduces the ability to obtain method parameter names using reflection.

Implementation:

import java.lang.reflect.Method;
import java.lang.reflect.Parameter;
import java.util.ArrayList;
import java.util.List;

public class ParameterNames {

    public static List<String> getParameterNames(Method method) {
        if (!method.isParameterNamesPresent()) {
            throw new IllegalArgumentException("Parameter names are not present!");
        }

        Parameter[] parameters = method.getParameters();
        List<String> parameterNames = new ArrayList<>();

        for (Parameter parameter : parameters) {
            parameterNames.add(parameter.getName());
        }

        return parameterNames;
    }

    // For testing
    public static void main(String[] args) throws Exception {
        Method getParameterNamesMethod = ParameterNames.class.getMethod("getParameterNames", Method.class);
        List<String> parameterNames = getParameterNames(getParameterNamesMethod);
        System.out.println("Method parameter names: " + parameterNames);
    }
}

Usage:

For a method named aMethod with a single parameter named aParam, the getParameterNames method will return ["aParam"].

Additional Information:

• Compiling with the -parameters flag or setting the parameterscompiler Argument to true in the Maven compiler plugin is necessary to generate parameter names in the class file.
• The Java 8 releases document Obtaining Names of Method Parameters in the official Java Tutorial provides more details on this feature.

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