public java.lang.String getIndexId() {
      java.lang.Object ref = indexId_;
      if (!(ref instanceof java.lang.String)) {
        com.google.protobuf.ByteString bs = (com.google.protobuf.ByteString) ref;
        java.lang.String s = bs.toStringUtf8();
        indexId_ = s;
        return s;
      } else {
        return (java.lang.String) ref;
      }
    }
<pre>
Optional. The ID for the index. This will become the final resource name
for the index. If the user does not specify this value, it will be
generated by system.

This value should be up to 63 characters, and valid characters
are /[a-z][0-9]-/. The first character must be a letter, the last could be
a letter or a number.
</pre>

<code>string index_id = 2 [(.google.api.field_behavior) = OPTIONAL];</code>

@return The indexId.
java-visionai/proto-google-cloud-visionai-v1/src/main/java/com/google/cloud/visionai/v1/CreateIndexRequest.java