How Can I Retrieve Method Parameter Names Using Java Reflection?

Can I Obtain Method Parameter Name Using Java Reflection?

In Java prior to version 8, obtaining method parameter names was not directly possible through reflection. However, with the introduction of the Java Reflection API in version 8, this capability was introduced.

Retrieving Parameter Names in Java 8

To retrieve the names of method parameters using Java 8 reflection, you can use the following approach:

1. Obtain the Method object of the method in question using reflection (Method.getMethod() or Class.getDeclaredMethod()).
2. Utilize the getParameters() method of the Method object to retrieve an array of Parameter objects.
3. Check if the parameter names are available by calling isNamePresent() on each Parameter object. If not, you cannot obtain the parameter names.
4. Retrieve the parameter names by calling getName() on the Parameter objects.

Code Example

The following code demonstrates how to retrieve method parameter names in Java 8:

import java.lang.reflect.Method;
import java.lang.reflect.Parameter;

public class MethodParameterNames {

    public static void main(String[] args) {
        try {
            // Get the class object
            Class<?> clazz = Class.forName("Whatever");

            // Get the method object
            Method method = clazz.getMethod("aMethod", int.class);

            // Get the parameter array
            Parameter[] parameters = method.getParameters();

            // Extract and print the parameter names
            for (Parameter parameter : parameters) {
                System.out.println(parameter.getName());
            }
        } catch (ClassNotFoundException | NoSuchMethodException e) {
            e.printStackTrace();
        }
    }
}

Additional Information

• For the code example above to work, you need to compile your code with the -parameters compiler argument to enable parameter name retention.
• The ability to obtain parameter names is a relatively new feature, so it may not be supported in all Java environments. Please check the compatibility of your Java version.

• For detailed documentation, refer to the following resources:

  • [Java Tutorial: Obtaining Names of Method Parameters](https://docs.oracle.com/javase/tutorial/reflect/methodparameterreflection.html#obtainingnames)
  • [Javadoc for Parameter Class](https://docs.oracle.com/javase/8/docs/api/java/lang/reflect/Parameter.html)

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