logback-android/src/main/java/ch/qos/logback/core/rolling/RollingFileAppender.java
@Override
  protected void subAppend(E event) {
    // The roll-over check must precede actual writing. This is the
    // only correct behavior for time driven triggers.

    // We need to synchronize on triggeringPolicy so that only one rollover
    // occurs at a time
    synchronized (triggeringPolicy) {
      if (triggeringPolicy.isTriggeringEvent(currentlyActiveFile, event)) {
        rollover();
      }
    }

    super.subAppend(event);
  }
@Override
  protected void subAppend(E event) {
    // The roll-over check must precede actual writing. This is the
    // only correct behavior for time driven triggers.

    // We need to synchronize on triggeringPolicy so that only one rollover
    // occurs at a time
    synchronized (triggeringPolicy) {
      if (triggeringPolicy.isTriggeringEvent(currentlyActiveFile, event)) {
        rollover();
      }
    }

    super.subAppend(event);
  }
This method differentiates RollingFileAppender from its super class.