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  1. PO
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    <p>The problem with the answer by Travis Brown is that he did not include all of the code. Here is the complete code, which does not compile.</p> <pre><code>import scala.Function; import scala.Function2; import scala.Tuple2; import scala.collection.immutable.WrappedString; import scala.runtime.AbstractFunction2; public class JavaTupleDemo { /** tupled() is implemented in Function2 (and therefore in AbstractFunction2) * @return str replicated x times */ static final Function2&lt;Integer, String, String&gt; foo = new AbstractFunction2&lt;Integer, String, String&gt;() { public String apply(Integer x, String str) { return new WrappedString(str).$times(x); } }; public static void main(String[] args) { // Invoke tupled function defined in Scala from Java using Tuple2 defined in Java Tuple2&lt;Object, String&gt; tuple = new Tuple2&lt;Object, String&gt;(3, "Hello, World! "); System.out.println(TupleDemo.tupledFoo1().apply(tuple)); // Invoke regular function defined in Java from Java System.out.println(JavaTupleDemo.foo.apply(3, "Hello, planet! ")); // Invoke tupled function defined in Java from Java using both the Scala and the Java Tuple2 instances System.out.println(JavaTupleDemo.foo.tupled().apply(tuple)); System.out.println(Function.tupled(JavaTupleDemo.foo).apply(tuple)); } } </code></pre> <p>The error messages are:</p> <pre><code>error: method apply in interface Function1&lt;T1,R&gt; cannot be applied to given types; required: Tuple2&lt;Integer,String&gt; found: Tuple2&lt;Object,String&gt; reason: actual argument Tuple2&lt;Object,String&gt; cannot be converted to Tuple2&lt;Integer,String&gt; by method invocation conversion where T1,R are type-variables: T1 extends Object declared in interface Function1 R extends Object declared in interface Function1 </code></pre> <p>You cannot simply cast tuple to a Tuple2&lt;Integer, String>. If you try the following:</p> <pre><code>System.out.println(JavaTupleDemo.foo.tupled().apply((Tuple2&lt;Integer, String&gt;)tuple)); System.out.println(Function.tupled(JavaTupleDemo.foo).apply((Tuple2&lt;Integer, String&gt;)tuple)); </code></pre> <p>The error message is:</p> <pre><code>error: inconvertible types required: Tuple2&lt;Integer,String&gt; found: Tuple2&lt;Object,String&gt; </code></pre> <p>The only way to make this compile is to do something really nasty - cast tuple first to an Object, then to a Tuple2&lt;Integer, String>:</p> <pre><code>System.out.println(JavaTupleDemo.foo.tupled().apply((Tuple2&lt;Integer, String&gt;)((Object)javaTuple))); System.out.println(Function.tupled(JavaTupleDemo.foo).apply((Tuple2&lt;Integer, String&gt;)((Object)javaTuple))); </code></pre> <p>Is there a better way to do this?</p>
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    1. POInvoking scala.Function.tupled() from Java
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    1. USMike Slinn
    1. USMike Slinn
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