Hey! I'm making a test tube item, which has an empty version of the item (prehistoric:test_tube), and another version of the item which is full of water (prehistoric:water_test_tube). I want to change the empty test tube to the filled one when you right click on water. How can I do this?

Code so far (not including imports)

public class TestTube extends Item {
    public TestTube(Properties properties) {
        super(properties);
    }

    @Override
    public ActionResultType onItemUseFirst(ItemStack stack, ItemUseContext context) {
        World world = context.getWorld();

        if (!world.isRemote) {
            PlayerEntity playerEntity = Objects.requireNonNull(context.getPlayer());
            BlockState clickedBlock = world.getBlockState(context.getPos());

            rightClickOnCertainBlockState(clickedBlock, context, playerEntity);
        }

        return super.onItemUseFirst(stack, context);
    }

    private void rightClickOnCertainBlockState(BlockState clickedBlock, ItemUseContext context,
                                               PlayerEntity playerEntity) {
        // Check if the player right-clicked water (with the test tube in-hand)
        if(blockIsWaterForTestTube(clickedBlock)) {
            // Fill test tube with water
        }
    }

    // Define if the clicked block was water
    private boolean blockIsWaterForTestTube(BlockState clickedBlock) {
        return clickedBlock.getBlock() == Blocks.WATER;
    }

    // public static void fillTestTubeWater
}

Thanks!

Do you want to have a behaviour like the bucket item ? If it is the case you should look in the class BucketItem available using ctrl n with intellij. The function used is : Item#use.