CarContract.kt

class CarContract : Contract {
    @Throws(IllegalArgumentException::class)
    override fun verify(tx: LedgerTransaction) {
        val (signers, _, value) = tx.commands.requireSingleCommand(Commands::class.java)
        val inputs = tx.inputStates
        val outputs = tx.outputStates
        if (value is Commands.Issue) {
            requireThat { 
                "Transaction must have no input states.".using(inputs.isEmpty())
                "Transaction must have exactly one output.".using(outputs.size == 1)
                "Output must be a CarState.".using(outputs[0] is CarState)

                // retrieve the CarState for the transaction
                val outputState = outputs[0] as CarState
                "The license plate number must be seven characters long.".using(outputState.getLicensePlateNumber().length() === 7)
                "Manufacturer must be required singer.".using(signers.contains(outputState.getManufacturer().getOwningKey()))
            }
        } else {
            throw IllegalArgumentException("Unrecognized command")
        }
    }

    interface Commands : CommandData {
        class Issue : Commands
    }

    companion object {
        var ID = "Sample.CarContract"
    }
}