Add java.lang.Double to JavaClasses

This is easier to read and more efficient as it
avoids repeated jimports of 'java.lang.Double' on each
Python -> Java image conversion request.

Author: elevans

src/imagej/_java.py

@@ -30,6 +30,10 @@ class MyJavaClasses(JavaClasses):
     significantly easier and more readable.
     """
 
+    @JavaClasses.java_import
+    def Double(self):
+        return "java.lang.Double"
+
     @JavaClasses.java_import
     def Throwable(self):
         return "java.lang.Throwable"

src/imagej/dims.py

@@ -184,8 +184,6 @@ def _assign_axes(xarr: xr.DataArray):
     :param xarr: xarray that holds the units
     :return: A list of ImageJ Axis with the specified origin and scale
     """
-    Double = sj.jimport("java.lang.Double")
-
     axes = [""] * len(xarr.dims)
 
     # try to get EnumeratedAxis, if not then default to LinearAxis in the loop
@@ -198,14 +196,14 @@ def _assign_axes(xarr: xr.DataArray):
         coords_arr = xarr.coords[dim].to_numpy()
 
         if _is_numeric_scale(coords_arr):
-            doub_coords = [Double(np.double(x)) for x in xarr.coords[dim]]
+            doub_coords = [jc.Double(np.double(x)) for x in xarr.coords[dim]]
         else:
             _logger.warning(
                 f"The {ax_type.label} axis is non-numeric and is translated "
                 "to a linear index."
             )
             doub_coords = [
-                Double(np.double(x)) for x in np.arange(len(xarr.coords[dim]))
+                jc.Double(np.double(x)) for x in np.arange(len(xarr.coords[dim]))
             ]
 
         # EnumeratedAxis is a new axis made for xarray, so is only present in