[ARROW-5920] [Java] Provide a utility to create the default comparator

java/algorithm/src/main/java/org/apache/arrow/algorithm/sort/DefaultVectorComparators.java

@@ -19,19 +19,49 @@
 
 import static org.apache.arrow.vector.BaseVariableWidthVector.OFFSET_WIDTH;
 
+import org.apache.arrow.vector.BaseFixedWidthVector;
 import org.apache.arrow.vector.BaseVariableWidthVector;
 import org.apache.arrow.vector.BigIntVector;
 import org.apache.arrow.vector.Float4Vector;
 import org.apache.arrow.vector.Float8Vector;
 import org.apache.arrow.vector.IntVector;
 import org.apache.arrow.vector.SmallIntVector;
 import org.apache.arrow.vector.TinyIntVector;
+import org.apache.arrow.vector.ValueVector;
 
 /**
  * Default comparator implementations for different types of vectors.
  */
 public class DefaultVectorComparators {
 
+  /**
+   * Create the default comparator for the vector.
+   * @param vector the vector.
+   * @param <T> the vector type.
+   * @return the default comparator.
+   */
+  public static <T extends ValueVector> VectorValueComparator<T> createDefaultComparator(T vector) {
+    if (vector instanceof BaseFixedWidthVector) {
+      if (vector instanceof TinyIntVector) {
+        return (VectorValueComparator<T>) new ByteComparator();
+      } else if (vector instanceof SmallIntVector) {
+        return (VectorValueComparator<T>) new ShortComparator();
+      } else if (vector instanceof IntVector) {
+        return (VectorValueComparator<T>) new IntComparator();
+      } else if (vector instanceof BigIntVector) {
+        return (VectorValueComparator<T>) new LongComparator();
+      } else if (vector instanceof Float4Vector) {
+        return (VectorValueComparator<T>) new Float4Comparator();
+      } else if (vector instanceof Float8Vector) {
+        return (VectorValueComparator<T>) new Float8Comparator();
+      }
+    } else if (vector instanceof BaseVariableWidthVector) {
+      return (VectorValueComparator<T>) new VariableWidthComparator();
+    }
+
+    throw new IllegalArgumentException("No default comparator for " + vector.getClass().getCanonicalName());
+  }
+
   /**
    * Default comparator for bytes.
    * The comparison is based on values, with null comes first.

java/algorithm/src/test/java/org/apache/arrow/algorithm/search/TestVectorSearcher.java

@@ -69,7 +69,8 @@ public void testBinarySearchInt() {
       negVector.set(0, -333);
 
       // do search
-      VectorValueComparator<IntVector> comparator = new DefaultVectorComparators.IntComparator();
+      VectorValueComparator<IntVector> comparator =
+              DefaultVectorComparators.createDefaultComparator(rawVector);
       for (int i = 0; i < VECTOR_LENGTH; i++) {
         int result = VectorSearcher.binarySearch(rawVector, comparator, rawVector, i);
         assertEquals(i, result);
@@ -100,7 +101,8 @@ public void testLinearSearchInt() {
       negVector.set(0, -333);
 
       // do search
-      VectorValueComparator<IntVector> comparator = new DefaultVectorComparators.IntComparator();
+      VectorValueComparator<IntVector> comparator =
+              DefaultVectorComparators.createDefaultComparator(rawVector);
       for (int i = 0; i < VECTOR_LENGTH; i++) {
         int result = VectorSearcher.linearSearch(rawVector, comparator, rawVector, i);
         assertEquals(i, result);
@@ -139,7 +141,7 @@ public void testBinarySearchVarChar() {
 
       // do search
       VectorValueComparator<BaseVariableWidthVector> comparator =
-              new DefaultVectorComparators.VariableWidthComparator();
+              DefaultVectorComparators.createDefaultComparator(rawVector);
       for (int i = 0; i < VECTOR_LENGTH; i++) {
         int result = VectorSearcher.binarySearch(rawVector, comparator, rawVector, i);
         assertEquals(i, result);
@@ -178,7 +180,7 @@ public void testLinearSearchVarChar() {
 
       // do search
       VectorValueComparator<BaseVariableWidthVector> comparator =
-              new DefaultVectorComparators.VariableWidthComparator();
+              DefaultVectorComparators.createDefaultComparator(rawVector);
       for (int i = 0; i < VECTOR_LENGTH; i++) {
         int result = VectorSearcher.linearSearch(rawVector, comparator, rawVector, i);
         assertEquals(i, result);

java/algorithm/src/test/java/org/apache/arrow/algorithm/sort/TestFixedWidthInPlaceVectorSorter.java

@@ -64,7 +64,7 @@ public void testSortInt() {
 
       // sort the vector
       FixedWidthInPlaceVectorSorter sorter = new FixedWidthInPlaceVectorSorter();
-      DefaultVectorComparators.IntComparator comparator = new DefaultVectorComparators.IntComparator();
+      VectorValueComparator<IntVector> comparator = DefaultVectorComparators.createDefaultComparator(vec);
 
       sorter.sortInPlace(vec, comparator);
 

java/algorithm/src/test/java/org/apache/arrow/algorithm/sort/TestFixedWidthOutOfPlaceVectorSorter.java

@@ -70,7 +70,7 @@ public void testSortByte() {
 
       // sort the vector
       FixedWidthOutOfPlaceVectorSorter sorter = new FixedWidthOutOfPlaceVectorSorter();
-      DefaultVectorComparators.ByteComparator comparator = new DefaultVectorComparators.ByteComparator();
+      VectorValueComparator<TinyIntVector> comparator = DefaultVectorComparators.createDefaultComparator(vec);
 
       TinyIntVector sortedVec =
               (TinyIntVector) vec.getField().getFieldType().createNewSingleVector("", allocator, null);
@@ -117,7 +117,7 @@ public void testSortShort() {
 
       // sort the vector
       FixedWidthOutOfPlaceVectorSorter sorter = new FixedWidthOutOfPlaceVectorSorter();
-      DefaultVectorComparators.ShortComparator comparator = new DefaultVectorComparators.ShortComparator();
+      VectorValueComparator<SmallIntVector> comparator = DefaultVectorComparators.createDefaultComparator(vec);
 
       SmallIntVector sortedVec =
               (SmallIntVector) vec.getField().getFieldType().createNewSingleVector("", allocator, null);
@@ -164,7 +164,7 @@ public void testSortInt() {
 
       // sort the vector
       FixedWidthOutOfPlaceVectorSorter sorter = new FixedWidthOutOfPlaceVectorSorter();
-      DefaultVectorComparators.IntComparator comparator = new DefaultVectorComparators.IntComparator();
+      VectorValueComparator<IntVector> comparator = DefaultVectorComparators.createDefaultComparator(vec);
 
       IntVector sortedVec = (IntVector) vec.getField().getFieldType().createNewSingleVector("", allocator, null);
       sortedVec.allocateNew(vec.getValueCount());
@@ -210,7 +210,7 @@ public void testSortLong() {
 
       // sort the vector
       FixedWidthOutOfPlaceVectorSorter sorter = new FixedWidthOutOfPlaceVectorSorter();
-      DefaultVectorComparators.LongComparator comparator = new DefaultVectorComparators.LongComparator();
+      VectorValueComparator<BigIntVector> comparator = DefaultVectorComparators.createDefaultComparator(vec);
 
       BigIntVector sortedVec = (BigIntVector) vec.getField().getFieldType().createNewSingleVector("", allocator, null);
       sortedVec.allocateNew(vec.getValueCount());
@@ -256,7 +256,7 @@ public void testSortFloat() {
 
       // sort the vector
       FixedWidthOutOfPlaceVectorSorter sorter = new FixedWidthOutOfPlaceVectorSorter();
-      DefaultVectorComparators.Float4Comparator comparator = new DefaultVectorComparators.Float4Comparator();
+      VectorValueComparator<Float4Vector> comparator = DefaultVectorComparators.createDefaultComparator(vec);
 
       Float4Vector sortedVec = (Float4Vector) vec.getField().getFieldType().createNewSingleVector("", allocator, null);
       sortedVec.allocateNew(vec.getValueCount());
@@ -302,7 +302,7 @@ public void testSortDobule() {
 
       // sort the vector
       FixedWidthOutOfPlaceVectorSorter sorter = new FixedWidthOutOfPlaceVectorSorter();
-      DefaultVectorComparators.Float8Comparator comparator = new DefaultVectorComparators.Float8Comparator();
+      VectorValueComparator<Float8Vector> comparator = DefaultVectorComparators.createDefaultComparator(vec);
 
       Float8Vector sortedVec = (Float8Vector) vec.getField().getFieldType().createNewSingleVector("", allocator, null);
       sortedVec.allocateNew(vec.getValueCount());

java/algorithm/src/test/java/org/apache/arrow/algorithm/sort/TestVariableWidthOutOfPlaceVectorSorter.java

@@ -22,6 +22,7 @@
 
 import org.apache.arrow.memory.BufferAllocator;
 import org.apache.arrow.memory.RootAllocator;
+import org.apache.arrow.vector.BaseVariableWidthVector;
 import org.apache.arrow.vector.VarCharVector;
 import org.junit.After;
 import org.junit.Assert;
@@ -65,8 +66,8 @@ public void testSortString() {
 
       // sort the vector
       VariableWidthOutOfPlaceVectorSorter sorter = new VariableWidthOutOfPlaceVectorSorter();
-      DefaultVectorComparators.VariableWidthComparator comparator =
-              new DefaultVectorComparators.VariableWidthComparator();
+      VectorValueComparator<BaseVariableWidthVector> comparator =
+              DefaultVectorComparators.createDefaultComparator(vec);
 
       VarCharVector sortedVec =
               (VarCharVector) vec.getField().getFieldType().createNewSingleVector("", allocator, null);