Passing a block of code from Java to a Scala object

Question

I have a generic utility in scala to Retry a certain piece of code logic n number of times.

RetryCode.scala

object RetryCode {
    def retry[T](timesRetry: Int)(block: => T): T = {
        def doBlock() = block
        breakable {
            for (i <- 0 until timesRetry) {
                try {
                    ...
                    doBlock()
                } catch {
                    ...
                }
            }
        }
    }
}

Test Unit in Scala:

class RetryCodeTest {
    test("success on 1st retry") {
        var i = 0
        val result = retry(5) {
          i = i + 1
          i
        }
        assert(result==1)
    }
}

I'd like to extend this functionality to a Java program

private void myMethod(int x) {
    try {
        // Code block to Retry 10 times
        ...
    } catch(Exception ex) {
        System.out.println("Error: " + ex.getMessage());
    }
}

How do I send a block of Java 7 code to my RetryCode object in Scala?

create instance of Java class in the Scala class? call myMethod within the loop? — OneCricketeer
– OneCricketeer, Commented Sep 9, 2016 at 20:51
Unfortunately that's not an option as the Scala object is used frequently else where in Scala code base. — AngryPanda
– AngryPanda, Commented Sep 9, 2016 at 20:52
I'd overload the retry() method in Scala with one that takes a Java Callable, and passes it to your real retry method. Then in your Java you could create an anonymous Callable (or a lamda expression in Java 8). Something along those lines. — erickson
– erickson, Commented Sep 10, 2016 at 4:36

Alexey Romanov · Accepted Answer · 2016-09-10 12:02:40Z

1

The signature of retry which Java sees is <T> T retry(int timesRetry, scala.Function0<T> block). So you need to instantiate a Function0, but extending it directly in Java won't work; instead you want

RetryCode.retry(10, new scala.runtime.AbstractFunction0<Integer> {
  @Override
  public Integer apply() { return something; }
});

(At least if I remember correctly and the static method is generated on RetryCode).

Note that in general you can't just assume a Scala API will be reasonably callable from Java; you may need to write a wrapper for it (in Scala).

answered Sep 10, 2016 at 12:02

Alexey Romanov

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1 Comment

AngryPanda Over a year ago

Unsure about this as things get quickly complicated with multiple arguments but +1 for the effort!

AngryPanda · Accepted Answer · 2016-09-11 00:26:46Z

0

I rewrote my Java 7 program in Scala.

answered Sep 11, 2016 at 0:26

AngryPanda

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