IllegalArgumentException with constructing class using reflection and array arguments

Question

running the following code:

public class Test {

    public Test(Object[] test){

    }

    public static void main(String[] args) throws Exception{
            Constructor cd = Test.class.getConstructor(Object[].class);
            Object[] objs = {1, 2, 3, 4, 5, 6, 7, 8};
            cd.newInstance(objs);
    }
}

I get the error :

Exception in thread "main" java.lang.IllegalArgumentException: wrong number of arguments
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:532)
    at groupd.poker.utils.tests.ai.nqueens.Test.main(Test.java:17)

Why is this?

Craig Suchanec · Accepted Answer · 2011-04-22 22:21:28Z

12

The newInstance() method of the constructor class takes an array of objects. Each item in the array is an argument of the constructor you are invoking. Your class's constructor takes an object array so you need to have an object array inside the array you pass to the new instance method

public static void main(String[] args) throws Exception{
            Constructor cd = Test.class.getConstructor(Object[].class);
            Object[] objs = {1, 2, 3, 4, 5, 6, 7, 8};
            Object[] passed = {objs};
            cd.newInstance(passed);
    }

answered Apr 22, 2011 at 22:21

Craig Suchanec

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