Setting a kotlin lambda from java

Question

So say I have some simple data class like this:

data class Transaction(
    val time: Long,
    val sender: String,
    val data: ByteArray
)

And in Kotlin I have the following method defined:

fun handleTransaction(transactionGetter: ()->Transaction) {
    // do something
}

How do I go about calling this method from Java?

I've tried trying to make a java lambda but can't figure it out. It is telling me that the parameter is supposed to be a Function0<Transaction> but I am not too sure how to define that.

Okay so, I figured out I can do this:

handleTransaction(new Function0<Transaction>() {
    @Override
    public Transaction invoke() {
        // handle getting transaction           
    }
});

Is that really the right way to do it? It is quite ugly.

() -> createTransaction() just like a Java Supplier<Transaction>. — JB Nizet
– JB Nizet, Commented Jan 24, 2020 at 16:48

ysakhno · Accepted Answer · 2020-01-24 16:56:37Z

2

If you're targeting at least JDK 8, you can do this (if function handleTransaction is defined in file Transaction.kt):

    public static void main(String[] args) {
        TransactionKt.handleTransaction(() -> new Transaction(
                Instant.now().toEpochMilli(), "system", new byte[0]));
    }

If you are targeting anything below JDK 8, then there is no other way other than what you already found.

answered Jan 24, 2020 at 16:56

ysakhno

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