CODEWITHSUNDEEP
javascala
Kevin Meredith
Kevin Meredith

Reputation: 41919

Calling Scala Method from Java - Set<Object> or Set<Long>?

Java

Set<Long> set = new HashSet<Long>();
set.add(100);
long x = 2;
foo(x, set);

Scala

def foo(a: Long, b: java.util.Set[Long])

Error:

could not parse error message:        
  required: long,Set<Object>    
  found: long,Set<Long>     
  reason: actual argument Set<Long> cannot be converted 
      to Set<Object> by method  invocation conversion

Then, I modified my Java code to resolve the compile-time error.

Set<Object> set = new HashSet<Object>();

However, the resolution of the compile-time error came at the expense of type safety. How can I properly resolve the above error?

EDIT

After @som-snytt resolved my issues here, I ran into this problem. I don't think it's the same question since , in my linked question, using, in Scala, foo(Long, java.util.Set[Long]) worked when calling (from Java) ScalaObject.foo(long, Set[Long])

Upvotes: 2

Views: 685

Answers (2)

Daniel C. Sobral
Daniel C. Sobral

Reputation: 297265

The types are wrong. The type of set in the Java code is java.util.Set[java.lang.Long], while the type in Scala is java.util.Set[scala.Long]. The scala.Long type is treated as the primitive long in Java, when not erased, and as java.lang.Object when erased (as you uncovered).

So either change Scala's type to Java's type to match. It's unfortunate that scala.Long erases to java.lang.Object, but necessary.

Upvotes: 5

mantithetical
mantithetical

Reputation: 1775

You probably want to import JavaConverters in this case.

import scala.collection.JavaConverters._
def foo(a: Long, b: java.util.Set[Long]) = ???

Upvotes: 0

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