Add Labeled Point, minor fix build

jvm-packages/xgboost4j/src/main/java/ml/dmlc/xgboost4j/LabeledPoint.java

@@ -0,0 +1,45 @@
+package ml.dmlc.xgboost4j;
+
+/**
+ * Labeled data point for training examples.
+ * Represent a sparse training instance.
+ */
+public class LabeledPoint {
+  /** Label of the point */
+  float label;
+  /** Weight of this data point */
+  float weight = 1.0f;
+  /** Feature indices, used for sparse input */
+  int[] indices = null;
+  /** Feature values */
+  float[] values;
+
+  private LabeledPoint() {}
+
+  /**
+   * Create Labeled data point from sparse vector.
+   * @param label The label of the data point.
+   * @param indices The indices
+   * @param values The values.
+   */
+  public static LabeledPoint fromSparseVector(float label, int[] indices, float[] values) {
+    LabeledPoint ret = new LabeledPoint();
+    ret.label = label;
+    ret.indices = indices;
+    ret.values = values;
+    return ret;
+  }
+
+  /**
+   * Create Labeled data point from dense vector.
+   * @param label The label of the data point.
+   * @param values The values.
+   */
+  public static LabeledPoint fromDenseVector(float label, float[] values) {
+    LabeledPoint ret = new LabeledPoint();
+    ret.label = label;
+    ret.indices = null;
+    ret.values = values;
+    return ret;
+  }
+}