Invoke private method with interface as argument

Question

Hi,

I've been attempting to invoke a private method whose argument is a parameter and I can't quite seem to get it right.

Here's kind of how the code looks so far:

public class TestClass {
   public TestClass(){
   }

   private void simpleMethod( Map<String, Integer> testMap) {
      //code logic
   }
}

Then I attempt to use this to invoke the private method:

//instance I would like to invoke simpleMethod on
TestClass testClassObject = new TestClass();

//Hashmap
Map <String, Integer> testMap = new HashMap <String, Integer>();

//method I want to invoke
Method simpleMethod = TestClass.class.getDeclaredMethod("simpleMethod", Map.class);
simpleMethod.setAccessible(true);

simpleMethod.invoke(testClassObject, testMap); //Throws an IllegalArgumentException 

As you can see, it throws an IllegalArgumentException. I've attempted to cast the hashmap back to a map, but that didn't work.

What am I doing wrong?

Answer 1

I just tested it, and your code works 100% fine here, when I instantiate your TestClass object like:

TestClass testClassObject = new TestClass();

Maybe you're using different imports (e.g. a different Map than java.util.Map)?

Answer 2

Method.invoke() takes two arguments. The first is the object to invoke the method upon. The second is an array of Objects, each representing a parameter. You need to change your invoke() call to:

simpleMethod.invoke(testClassObject, new Object[]{testMap});

Answer 3

Everything works just as expected and prints "simpleMethod invoked".

TestClass.java

import java.util.Map;

public class TestClass {
    public TestClass() {
    }
    private void simpleMethod(Map<String, Integer> testMap) {
        System.err.println("simpleMethod invoked");
    }
}

Caller.java

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.HashMap;
import java.util.Map;

public class Caller {
    public static void main(String[] args) throws IllegalArgumentException,
            IllegalAccessException, InvocationTargetException,
            SecurityException, NoSuchMethodException {
        // Hashmap
        Map<String, Integer> testMap = new HashMap<String, Integer>();

        // method I want to invoke
        Method simpleMethod = TestClass.class.getDeclaredMethod("simpleMethod",
                Map.class);
        simpleMethod.setAccessible(true);

        TestClass testClassObject = new TestClass();
        simpleMethod.invoke(testClassObject, testMap);
    }
}

Answer 4

The code as posted works fine for me. Tweaking the code a little, I get an IllegalArgumentException when testMap is null. "wrong number of arguments".