cdm/src/main/java/ucar/nc2/NetcdfFileWriter.java
public Variable addVariable(Group g, String shortName, DataType dataType, List<Dimension> dims) {
    if (g == null) g = ncfile.getRootGroup();
    Variable oldVar = g.findVariable(shortName);
    if (oldVar != null) return null;
    return addVariable(g, null, shortName, dataType, dims);
  }
public Variable addVariable(Group g, String shortName, DataType dataType, List<Dimension> dims) {
    if (g == null) g = ncfile.getRootGroup();
    Variable oldVar = g.findVariable(shortName);
    if (oldVar != null) return null;
    return addVariable(g, null, shortName, dataType, dims);
  }
Add a variable to the file. Must be in define mode.

@param g         add to this group in the new file
@param shortName name of Variable, must be unique with the file.
@param dataType  type of underlying element
@param dims      list of Dimensions for the variable in the new file, must already have been added.
Use a list of length 0 for a scalar variable.
@return the Variable that has been added, or null if a Variable with shortName already exists in the group