Add javadocs and copyright

extensions/tokenizers/src/main/java/ai/djl/huggingface/tokenizers/jni/CharSpan.java

@@ -1,19 +1,49 @@
+/*
+ * Copyright 2022 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"). You may not use this file except in compliance
+ * with the License. A copy of the License is located at
+ *
+ * http://aws.amazon.com/apache2.0/
+ *
+ * or in the "license" file accompanying this file. This file is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES
+ * OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions
+ * and limitations under the License.
+ */
+
+/** A class holds character span information. */
 package ai.djl.huggingface.tokenizers.jni;
 
 public class CharSpan {
     private final int start;
     private final int end;
 
+    /**
+     * Constructs a new {@code CharSpan} instance.
+     *
+     * @param start the start position
+     * @param end the end position
+     */
     public CharSpan(int start, int end) {
         this.start = start;
         this.end = end;
     }
 
-    public double getStart() {
+    /**
+     * Returns the start position.
+     *
+     * @return the start position
+     */
+    public int getStart() {
         return start;
     }
 
-    public double getEnd() {
+    /**
+     * Returns the end position.
+     *
+     * @return the end position
+     */
+    public int getEnd() {
         return end;
     }
 }