Make DataSize constants final

spring-core/src/main/java/org/springframework/util/unit/DataSize.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2019 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -41,22 +41,22 @@ public final class DataSize implements Comparable<DataSize> {
 	/**
 	 * Bytes per Kilobyte.
 	 */
-	private static long BYTES_PER_KB = 1024;
+	private static final long BYTES_PER_KB = 1024;
 
 	/**
 	 * Bytes per Megabyte.
 	 */
-	private static long BYTES_PER_MB = BYTES_PER_KB * 1024;
+	private static final long BYTES_PER_MB = BYTES_PER_KB * 1024;
 
 	/**
 	 * Bytes per Gigabyte.
 	 */
-	private static long BYTES_PER_GB = BYTES_PER_MB * 1024;
+	private static final long BYTES_PER_GB = BYTES_PER_MB * 1024;
 
 	/**
 	 * Bytes per Terabyte.
 	 */
-	private static long BYTES_PER_TB = BYTES_PER_GB * 1024;
+	private static final long BYTES_PER_TB = BYTES_PER_GB * 1024;
 
 
 	private final long bytes;