ARROW-6264: [Java] There is no need to consider byte order in ArrowBufHasher

According to the discussion in apache#5063 (comment), Arrow has a mechanism to make sure the data is stored in little-endian, so there is no need to check byte order.

Closes apache#5098 from liyafan82/fly_0816_order and squashes the following commits:

538ce59 <liyafan82> ARROW-6264  There is no need to consider byte order in ArrowBufHasher

Authored-by: liyafan82 <fan_li_ya@foxmail.com>
Signed-off-by: Pindikura Ravindra <ravindra@dremio.com>

Author: liyafan82

memory/src/main/java/org/apache/arrow/memory/util/ArrowBufPointer.java

@@ -17,8 +17,6 @@
 
 package org.apache.arrow.memory.util;
 
-import java.nio.ByteOrder;
-
 import org.apache.arrow.memory.util.hash.ArrowBufHasher;
 import org.apache.arrow.memory.util.hash.SimpleHasher;
 import org.apache.arrow.util.Preconditions;
@@ -31,8 +29,6 @@
  */
 public final class ArrowBufPointer {
 
-  public static final boolean LITTLE_ENDIAN = ByteOrder.nativeOrder() == ByteOrder.LITTLE_ENDIAN;
-
   /**
    * The hash code when the arrow buffer is null.
    */

memory/src/main/java/org/apache/arrow/memory/util/hash/MurmurHasher.java

@@ -20,8 +20,6 @@
 import static io.netty.util.internal.PlatformDependent.getByte;
 import static io.netty.util.internal.PlatformDependent.getInt;
 
-import org.apache.arrow.memory.util.ArrowBufPointer;
-
 import io.netty.buffer.ArrowBuf;
 
 /**
@@ -93,9 +91,6 @@ public static int hashCode(long address, int length, int seed) {
     int hash = seed;
     while (index + 4 <= length) {
       int intValue = getInt(address + index);
-      if (!ArrowBufPointer.LITTLE_ENDIAN) {
-        intValue = Integer.reverseBytes(intValue);
-      }
       hash = combineHashCode(hash, intValue);
       index += 4;
     }

memory/src/main/java/org/apache/arrow/memory/util/hash/SimpleHasher.java

@@ -21,8 +21,6 @@
 import static io.netty.util.internal.PlatformDependent.getInt;
 import static io.netty.util.internal.PlatformDependent.getLong;
 
-import org.apache.arrow.memory.util.ArrowBufPointer;
-
 import io.netty.buffer.ArrowBuf;
 
 /**
@@ -61,20 +59,13 @@ public int hashCode(long address, int length) {
     int index = 0;
     while (index + 8 <= length) {
       long longValue = getLong(address + index);
-      if (!ArrowBufPointer.LITTLE_ENDIAN) {
-        // assume the buffer is in little endian
-        longValue = Long.reverseBytes(longValue);
-      }
       int longHash = getLongHashCode(longValue);
       hashValue = combineHashCode(hashValue, longHash);
       index += 8;
     }
 
     while (index + 4 <= length) {
       int intValue = getInt(address + index);
-      if (!ArrowBufPointer.LITTLE_ENDIAN) {
-        intValue = Integer.reverseBytes(intValue);
-      }
       int intHash = intValue;
       hashValue = combineHashCode(hashValue, intHash);
       index += 4;