我的代碼違反了 DRY 原則，但不確定如何進行重構

Question

我對 OOP 非常陌生，並且在 Java 中編寫了一些用於在不同長度單位之間轉換雙精度值的類，但是我意識到我違反了 DRY 原則，因為類似的類基本上做同樣的事情。

問題 1：在這種情況下，創建計量單位的更好解決方案是什么？

問題 2：我想在 'lengthConverter' class 中完成所有轉換，但我意識到它在多個類之間進行了拆分。 將 'Feet' class 中的 'convertTo' 方法放入 'lengthConverter' class 等每個附加單元是否有意義？

public class LengthConverter {

private Inches inches = new Inches();
private Feet feet = new Feet();
private Meters meters = new Meters();
private Miles miles = new Miles();
private Millimeters millimeters = new Millimeters();
private Centimeters centimeters = new Centimeters();
private Kilometers kilometers = new Kilometers();
private Yards yards = new Yards();

public LengthConverter() {
}

public double convert(String origUnit, double length, String toUnit) {
    double result = 0;
    switch (origUnit) {
        case "cm":
            centimeters.setLength(length);
            result = centimeters.convertTo(toUnit);
            break;
        case "ft":
            feet.setLength(length);
            result = feet.convertTo(toUnit);
            break;
        case "in":
            inches.setLength(length);
            result = inches.convertTo(toUnit);
            break;
        case "km":
            kilometers.setLength(length);
            result = kilometers.convertTo(toUnit);
            break;
        case "m":
            meters.setLength(length);
            result = meters.convertTo(toUnit);
            break;
        case "mi":
            miles.setLength(length);
            result = miles.convertTo(toUnit);
            break;
        case "mm":
            millimeters.setLength(length);
            result = millimeters.convertTo(toUnit);
            break;
        case "yd":
            yards.setLength(length);
            result = yards.convertTo(toUnit);
            break;
        default:
            System.out.println("Error: incorrect input");
    }
    return result;
}

public class Feet {
final private double FOOT_TO_CM = 30.48;
final private double FOOT_TO_INCH = 12;
final private double FOOT_TO_KM = 0.000305;
final private double FOOT_TO_METER = 0.3048;
final private double FOOT_TO_MILE = 0.000189;
final private double FOOT_TO_MM = 304.8;
final private double FOOT_TO_YD = 0.333333;
final private double FOOT = 1;

private double length;

public Feet() {
}

public void setLength(double length) {
    this.length = length;
}

public double convertTo(String unit) {
    double result = 0;
    switch (unit) {
        case "in":
            result = length * FOOT_TO_INCH;
            break;
        case "m":
            result = length * FOOT_TO_METER;
            break;
        case "mi":
            result = length * FOOT_TO_MILE;
            break;
        case "mm":
            result = length * FOOT_TO_MM;
            break;
        case "cm":
            result = length * FOOT_TO_CM;
            break;
        case "km":
            result = length * FOOT_TO_KM;
            break;
        case "yd":
            result = length * FOOT_TO_YD;
            break;
        case "ft":
            result = length * FOOT;
            break;
    }
    return result;
}

}

Answer 1

您可以使用 Java 枚舉。 查看TimeUnit （特別是TimeUnit.convert(long,TimeUnit) ）進行轉換。 源代碼在GitHub上可用。