How do I get the class of an array via Class.forName(...)?

Question

Let's say I have a method do expecting an array of arguments of some class E:

public class D {

    public void do(E ..arg){}

}

public static void main(String[] args) {
    Class z = Class.forName("D");
    Class e = Class.forName("E");
    Method m = z.getDeclaredMethod("do", e);
}

I want to get the method and the class using reflection, but this throws a

java.lang.NoSuchMethodException

do is not a static method, I tried z.getMethod("do",e); didn't work — Anshul Khandelwal
– Anshul Khandelwal, Commented May 25, 2020 at 19:15
I also tried z.getMethod("do",Object[].class); That also didn't work; — Anshul Khandelwal
– Anshul Khandelwal, Commented May 25, 2020 at 19:17
You are trying to to get a reference to a method with the name do and a single parameter of type E. But the method has a E[] parameter... — f1sh
– f1sh, Commented May 25, 2020 at 19:24
Does that code compile at all? I might be a bit rusty in java but I'm not 100% sure you can call a method do and varargs with .. instead of ... — Balastrong
– Balastrong, Commented May 25, 2020 at 19:25
You can't do it with e, because that's not what the method expects. — cegredev
– cegredev, Commented May 25, 2020 at 19:26

cegredev · Accepted Answer · 2020-05-26 20:42:53Z

4

do expects an array of E.

So instead of passing getDeclaredMethod(...) e, pass it E[].class:

Method m = z.getDeclaredMethod("do", E[].class);

If you have to use Class.forName(...), you'll need to modify the name a bit. If you print out any object array's class, you'll see that it has a [L in the front and a ; at the end. Just add that to your argument and it should work:

Class<?> e = Class.forName("[L" + "E" + ";");
Method m = z.getDeclaredMethod("do", e);

You could also write a method that returns the class-name of an array with any amount of dimensions:

public static String getArrayClassName(int dimensions, String base) {
    return "[".repeat(dimensions) + "L" + base + ";";
}

edited May 26, 2020 at 20:42

answered May 25, 2020 at 19:25

cegredev

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4 Comments

Anshul Khandelwal Over a year ago

Is there any way, I can get "e" as an array of "E" using reflection? I have a requirement to do with Class e = Class.forName("E");

Anshul Khandelwal Over a year ago

Actually I have the String "E" and using this I want to getMethod.

cegredev Over a year ago

@AnshulKhandelwal There is, give me a sec.

Jorn Vernee Over a year ago

See also Class::arrayType since Java 12.

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