code: public Axis addLabel(String[] label, double[] location) {
          if (label.length != location.length) {
              throw new IllegalArgumentException("Label size and location size don't match.");
          }
  
          if (labels == null) {
              labels = new HashMap<>();
          }
  
          for (int i = 0; i < label.length; i++) {
              labels.put(label[i], location[i]);
          }
  
          setSlice();
          initGridLines();
          initGridLabels();
          return this;
      }
docs: Add a label to the axis at given location.