code: private void obtainQualityScoresFromQualityString() {
          int total = 0;
          this.maximumQuality = Integer.MIN_VALUE;
          this.minimumQuality = Integer.MAX_VALUE;
          // quality int array initialization
          qualityScoresArray = new int[this.quality.length()];
  
          // Transform each character in the quality String into a integer, depending on
          // the quality scale, and obtain the average, minimum and maximum values
          for (int i = 0; i < this.quality.length(); i++) {
              char c = this.quality.charAt(i);
              qualityScoresArray[i] = c - FastQ.SCALE_OFFSET[this.encoding];
              total += this.qualityScoresArray[i];
  
              this.maximumQuality = Math.max(this.qualityScoresArray[i], this.maximumQuality);
              this.minimumQuality = Math.min(this.qualityScoresArray[i], this.minimumQuality);
          }
          this.averageQuality = (double) total / this.quality.length();
      }
docs: This method obtain the quality scores array corresponding to the quality char sequence,
  depending on the sequence's encoding, and calculate sequence's average quality and
  maximum and minimum individual quality scores