Use EMPTY constant instance for empty byte array to safe memory

fix #17

Author: patrickfav

CHANGELOG

@@ -7,6 +7,7 @@
  * add `from(Inputstream stream, int maxlength)` limiting stream reading constructor #13
  * add indexOf() with `fromIndex` parameter #14
  * add support for base64 url safe encoding #15
+ * use EMPTY constant instance for empty byte array to safe memory #16
 
 ## v0.6.0
 

src/main/java/at/favre/lib/bytes/Bytes.java

@@ -60,6 +60,8 @@
 @SuppressWarnings("WeakerAccess")
 public class Bytes implements Comparable<Bytes>, Serializable, Iterable<Byte> {
 
+    private final static Bytes EMPTY = Bytes.wrap(new byte[0]);
+
     /* FACTORY ***************************************************************************************************/
 
     /**
@@ -90,10 +92,10 @@ public static Bytes allocate(int length, byte defaultValue) {
     /**
      * Creates an Byte instance with an internal empty byte array. Same as calling {@link #allocate(int)} with 0.
      *
-     * @return new instance
+     * @return the empty instance (always the same reference
      */
     public static Bytes empty() {
-        return allocate(0);
+        return EMPTY;
     }
 
     /**
@@ -120,7 +122,7 @@ public static Bytes wrap(Bytes bytes) {
      * @return new instance
      */
     public static Bytes wrapNullSafe(byte[] array) {
-        return wrap(array != null ? array : new byte[0]);
+        return array != null ? wrap(array) : empty();
     }
 
     /**
@@ -175,7 +177,7 @@ public static Bytes from(byte[] byteArrayToCopy) {
      * @return new instance
      */
     public static Bytes fromNullSafe(byte[] byteArrayToCopy) {
-        return from(byteArrayToCopy != null ? byteArrayToCopy : new byte[0]);
+        return byteArrayToCopy != null ? from(byteArrayToCopy) : empty();
     }
 
     /**

src/test/java/at/favre/lib/bytes/BytesConstructorTests.java

@@ -26,13 +26,10 @@
 import org.junit.Test;
 import org.junit.rules.TemporaryFolder;
 
-import java.io.ByteArrayInputStream;
-import java.io.DataInput;
-import java.io.DataInputStream;
-import java.io.File;
-import java.io.FileOutputStream;
+import java.io.*;
 import java.math.BigInteger;
 import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
 import java.nio.charset.Charset;
 import java.nio.charset.StandardCharsets;
 import java.text.Normalizer;
@@ -82,6 +79,11 @@ public void empty() {
         assertEquals(0, Bytes.empty().length());
         assertEquals(Bytes.allocate(0), Bytes.empty());
         assertArrayEquals(new byte[0], Bytes.empty().array());
+        assertSame(Bytes.empty(), Bytes.empty());
+
+        Bytes empty = Bytes.empty();
+        empty = empty.byteOrder(ByteOrder.LITTLE_ENDIAN);
+        assertNotSame(Bytes.empty(), empty);
     }
 
     @Test