Getting error when using object[] in constructor when using reflections in java

Question

So, the title sais everything. When i try to pass arguments in an Object array using .newInstance i get an error:

java.lang.IllegalArgumentException: argument type mismatch at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source) at java.lang.reflect.Constructor.newInstance(Unknown Source) at me.voxed.textrpg.RoomCreator.setNorth(RoomCreator.java:44) at me.voxed.textrpg.Game.(Game.java:89) at me.voxed.textrpg.Program.main(Program.java:6)

This is the function im using:

    public void setNorth(String block, String... args){
    try {
        Object[] argsObj = args;
        Class<? extends Block> clazz = (Class<? extends Block>) (GameRegistry.getBlock(block));
        _north = clazz.asSubclass(Block.class).getConstructor(Object[].class).newInstance(argsObj);
    } catch (InstantiationException | IllegalAccessException | IllegalArgumentException | InvocationTargetException
            | NoSuchMethodException | SecurityException e) {
        e.printStackTrace();
    }
}

And clazz is this class:

public class BlockNPCSpawnBars extends BlockNPC {

public BlockNPCSpawnBars(Object[] args) {
    super(args);
}

What am i doing wrong?

check this answer stackoverflow.com/questions/5760569/…

luanjot
– luanjot

2015-11-21 16:04:12 +00:00
Commented Nov 21, 2015 at 16:04 — luanjot
– luanjot, Commented Nov 21, 2015 at 16:04
Darn! I should have searched more :/

Voxed
– Voxed

2015-11-21 16:13:57 +00:00
Commented Nov 21, 2015 at 16:13 — Voxed
– Voxed, Commented Nov 21, 2015 at 16:13

Radiodef · Accepted Answer · 2015-11-21 16:05:43Z

2

newInstance takes variable arguments. When you pass it an array, it translates to a varargs call, as if each element in that array were a separate argument to the constructor.

This is generally solved like the following:

...newInstance((Object) argsObj);

That will ensure the array is passed as the singular argument, like your actual constructor is expecting.

answered Nov 21, 2015 at 16:05

Radiodef

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3 Comments

Voxed Over a year ago

That was fast! Thanks for an informative and quick solution. :)

Radiodef Over a year ago

No problem. If you think the issue's adequately solved, you can consider accepting my answer. meta.stackexchange.com/q/5234/244864 Also, note that the explicit (Object) cast is basically just a shorthand for the code shown in the link from @luanjot. (Varargs sees the Object and creates an array around it with 1 element.)

Voxed Over a year ago

I was going to, i dont think i can accept an answer until 10 minutes have passed. Thanks again :)

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