[jvm-packages] separate classification and regression model and integrate with ML package (#1608)

jvm-packages/xgboost4j/src/main/scala/ml/dmlc/xgboost4j/scala/EvalTrait.scala

@@ -38,6 +38,8 @@ trait EvalTrait extends IEvaluation {
   def eval(predicts: Array[Array[Float]], dmat: DMatrix): Float
 
   private[scala] def eval(predicts: Array[Array[Float]], jdmat: java.DMatrix): Float = {
+    require(predicts.length == jdmat.getLabel.length, "predicts size and label size must match " +
+      s" predicts size: ${predicts.length}, label size: ${jdmat.getLabel.length}")
     eval(predicts, new DMatrix(jdmat))
   }
 }