8257750: writeBuffer field of java.io.DataOutputStream should be final

Reviewed-by: lancea, naoto

Author: Brian Burkhalter

src/java.base/share/classes/java/io/DataOutputStream.java

@@ -50,6 +50,8 @@ public class DataOutputStream extends FilterOutputStream implements DataOutput {
      */
     private byte[] bytearr = null;
 
+    private final byte[] writeBuffer = new byte[8];
+
     /**
      * Creates a new data output stream to write data to the specified
      * underlying output stream. The counter {@code written} is
@@ -207,8 +209,6 @@ public final void writeInt(int v) throws IOException {
         incCount(4);
     }
 
-    private byte writeBuffer[] = new byte[8];
-
     /**
      * Writes a {@code long} to the underlying output stream as eight
      * bytes, high byte first. In no exception is thrown, the counter