将代码块从Java传递到Scala对象

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 ?

Answer 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).

Answer 2

我在Scala重写了Java 7程序。