java reflection to invoke a method that takes a Comparable[] argument

Question

I have a class with a `static` method which takes a `Comparable[]` as argument. I need to find and invoke the method .I tried the following with `java reflection` ``` class X{ public static void sort(Comparable[] a){ System.out.println("sorting"); } public static void read(String name){ System.out.println("name="+name); } } ... public static void main(String[] args) throws ClassNotFoundException, SecurityException, NoSuchMethodException, IllegalArgumentException, IllegalAccessException, InvocationTargetException, InstantiationException { String[] a= new String[]{"E","X","A","M","P","L","E"}; Class xc = Class.forName("my.javacode.X"); Method m2 = xc.getMethod("read", java.lang.String.class); m2.invoke(null, "jon"); Method m1 = xc.getMethod("sort", Comparable[].class); System.out.println(m1); m1.invoke(null, a); } .. ``` this produced an exception ``` name=jon public static void my.javacode.X.sort(java.lang.Comparable[]) Exception in thread "main" java.lang.IllegalArgumentException: wro…

Accepted Answer

When you call `Method.invoke` with this signature:

```
public Object invoke(Object obj, Object... args)
```

... the varargs parameter is only used as a varargs parameter when it would fail otherwise.

So this call:

```
m2.invoke(null, "jon");
```

is equivalent to:

```
m2.invoke(null, new Object[] {"jon"});
```

But `String[]` is implicitly convertible to `Object[]`, so this call:

```
m1.invoke(null, a);
```

is not expanded to wrap `a` in an `Object[]`. It's trying to call the method as if it's got 7 string parameters rather than one array parameter.

Two options:

- Declare `a` as type `Object` rather than `String[]`, which will then make the compiler perform the wrapping for you.

Explicitly wrap it in an array:

```
m1.invoke(null, new Object[] { a });
```

Either should be fine.

java reflection to invoke a method that takes a Comparable[] argument

Solution

Problem