Add getters

Author: Feynman Liang

mllib/src/main/scala/org/apache/spark/mllib/fpm/PrefixSpan.scala

@@ -53,6 +53,12 @@ class PrefixSpan private (
    */
   def this() = this(0.1, 10)
 
+  /**
+   * Get the minimal support (i.e. the frequency of occurrence before a pattern is considered
+   * frequent).
+   */
+  def getMinSupport(): Double = this.minSupport
+
   /**
    * Sets the minimal support level (default: `0.1`).
    */
@@ -63,10 +69,16 @@ class PrefixSpan private (
     this
   }
 
+  /**
+   * Gets the maximal pattern length (i.e. the length of the longest sequential pattern to consider.
+   */
+  def getMaxPatternLength(): Double = this.maxPatternLength
+
   /**
    * Sets maximal pattern length (default: `10`).
    */
   def setMaxPatternLength(maxPatternLength: Int): this.type = {
+    // TODO: support unbounded pattern length when maxPatternLength = 0
     require(maxPatternLength >= 1,
       "The maximum pattern length value must be greater than 0.")
     this.maxPatternLength = maxPatternLength