@java.lang.Override
  public java.lang.String getFilePrefix() {
    java.lang.Object ref = filePrefix_;
    if (ref instanceof java.lang.String) {
      return (java.lang.String) ref;
    } else {
      com.google.protobuf.ByteString bs = (com.google.protobuf.ByteString) ref;
      java.lang.String s = bs.toStringUtf8();
      filePrefix_ = s;
      return s;
    }
  }
<pre>
Required. File name prefix for the generated sprite sheets. If multiple
sprite sheets are added to the channel, each must have a unique file
prefix.
Each sprite sheet has an incremental 10-digit zero-padded suffix starting
from 0 before the extension, such as `sprite_sheet0000000123.jpeg`.
</pre>

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

@return The filePrefix.
java-video-live-stream/proto-google-cloud-live-stream-v1/src/main/java/com/google/cloud/video/livestream/v1/SpriteSheet.java