Make Buffer a sealed interface

Author: oschwald

src/main/java/com/maxmind/db/Buffer.java

@@ -14,7 +14,7 @@
  * <p>All underlying {@link java.nio.ByteBuffer}s are read-only to prevent
  * accidental modification of shared data.
  */
-interface Buffer {
+sealed interface Buffer permits SingleBuffer, MultiBuffer {
     /**
      * Returns the total capacity of this buffer in bytes.
      *

src/main/java/com/maxmind/db/MultiBuffer.java

@@ -21,7 +21,7 @@
  * <p>All underlying {@link ByteBuffer}s are read-only to prevent accidental
  * modification of shared data.
  */
-class MultiBuffer implements Buffer {
+final class MultiBuffer implements Buffer {
 
     /** Default maximum size per underlying chunk. */
     static final int DEFAULT_CHUNK_SIZE = Integer.MAX_VALUE - 8;

src/main/java/com/maxmind/db/SingleBuffer.java

@@ -16,7 +16,7 @@
  * <p>The underlying {@link ByteBuffer} is read-only to prevent accidental
  * modification of shared data.
  */
-class SingleBuffer implements Buffer {
+final class SingleBuffer implements Buffer {
 
     private final ByteBuffer buffer;