有没有简单的方法可以返回整数值或双精度值？

Question

I'm recreating something similar to pandas dataframe in java to read csv files and manipulate data. I have everything coded as generic to handle any type of column in a csv file as well as auto declaration to wrapper classes such as Integer and Double if it is a number. The problem is that now I'm writing functions that will only concern Numeric columns, but I still need to do a decent amount of casting to get the actual values which I would like to find a more elegant solution to.

I have tried casting within the methods and it works but I'm looking for a way to just return the numeric value if it is a number within the column class to avoid doing this for future functions:

  //the basic structure
  public class Column<T> {
  public String type; //column type
  public String name; //column name
  public ArrayList<T> values; //array of values
...
  public T getValue(int index) {
      return values.get(index);
  }
}


//in another file is the problem
public static double variance(Column c) {
    double mean = mean(c);
    double var = 0;
    for(int i = 0;i < c.getLength();i++) {
                            // here is the problem
        var = Math.pow((((Number) c.getValue(i)).doubleValue()-mean),2);
    }
    return var/c.getLength();
  }

Answer 1

If you have the freedom to modify your Column class or make another, more specific subclass, instead of doing a cast outside the object, you could add methods to return a double internally if it's a double, an int if it's an int, etc, since in your example you know that Column is a Column<Number> . For example:

public class DoubleColumn extends Column<Number> {
    @Override
    public Double getValue(int index) {
        return super.getValue(index).doubleValue();
    }
}

Then you can modify your variance method accordingly to take a DoubleColumn instead of a Column .