不同类型单位的抽象类

Question

我有不同的类，代表不同的单位（体积、重量、距离），枚举的值用于将转换值存储为基本类型。

问题是有很多代码重复和我相信有一种优雅的方法来编写抽象类可以避免它。我不知道我应该如何声明这个类。以下是卷类：

import java.math.BigDecimal;
import lombok.Data;
@Data
public class Volume {
public enum Unit
{
    CUBIC_METER(new BigDecimal("1")), // CUBIC_METER
    // 1 m3 = 61023.7 inch3
    CUBIC_INCH(new BigDecimal("61023.7"));
    private Unit(BigDecimal m3Value)
    {
        this.m3Value = m3Value;
    }
    public final BigDecimal m3Value;
}
// internally, we store the volume in m3
private final   BigDecimal  volumeInM3;
public Volume()
{
    volumeInM3 = BigDecimal.ZERO;
}
public Volume(final String volumeValue, final Unit volumeUnit)
{
    this(new BigDecimal(volumeValue), volumeUnit);
}
public Volume(final BigDecimal volumeValue, final Unit volumeUnit)
{
    if (volumeValue.signum() == 0)
    {
        volumeInM3 = BigDecimal.ZERO;
    }
    else
    {
        volumeInM3 = volumeValue.divide(volumeUnit.m3Value, NumberUtil.MC);
    }
}
/**
 * Return the volume in the unit given in param
 * @param volumeUnit
 * @return
 */
public BigDecimal getAs(final Unit volumeUnit)
{
    return volumeInM3.multiply(volumeUnit.m3Value, NumberUtil.MC);
}
public Volume add(final Volume volumeToAdd)
{
    BigDecimal newVolumeValue = volumeToAdd.volumeInM3.add(volumeInM3, NumberUtil.MC);
    return new Volume(newVolumeValue, Volume.Unit.CUBIC_METER);
}
public Volume divide(final Volume divisor)
{
    BigDecimal newVolumeValue = volumeInM3.divide(divisor.volumeInM3, NumberUtil.MC);
    return new Volume(newVolumeValue, Volume.Unit.CUBIC_METER);
}
public boolean isZero()
{
    if (volumeInM3.signum() == 0)
        return true;
    return false;
}
public boolean isEqual(final Volume another)
{
    if (volumeInM3.compareTo(another.volumeInM3) == 0)
        return true;
    return false;
}
}

这是非常相似的重量等级：

import java.math.BigDecimal;
import lombok.Data;
@Data
public class Weight {
// the value stored with enum is the value used to convert the unit to kilogramm, 
// wich is the reference unit
public enum Unit
{
    KILOGRAM(new BigDecimal("1")),
    // 1 kg = 1000 g 
    GRAM(new BigDecimal("1000")),
    // 1 kg = 2.20462 pounds
    POUND(new BigDecimal("2.20462"));
    private Unit(BigDecimal kgValue)
    {
        this.kgValue = kgValue;
    }
    private final BigDecimal kgValue;
}
// internally, we store the weight inKg
private final BigDecimal weightInKg;
public Weight()
{
    weightInKg = BigDecimal.ZERO;
}
public Weight(final String weightValue, final Unit weightUnit)
{
    this(new BigDecimal(weightValue), weightUnit);
}
public Weight(final BigDecimal weightValue, final Unit weightUnit)
{
    if (weightValue.signum() == 0)
    {
        weightInKg = BigDecimal.ZERO;
    }
    else
    {
        weightInKg = weightValue.divide(weightUnit.kgValue, NumberUtil.MC);
    }
}
/**
 * Return the weight in the unit given in param
 * @param weightUnit
 * @return
 */
public BigDecimal getAs(final Unit weightUnit)
{
    return weightInKg.multiply(weightUnit.kgValue, NumberUtil.MC);
}
public Weight add(final Weight weightToAdd)
{
    BigDecimal newWeightValue = weightToAdd.weightInKg.add(weightInKg, NumberUtil.MC);
    return new Weight(newWeightValue, Weight.Unit.KILOGRAM);
}
public Weight divide(final Weight divisor)
{
    BigDecimal newWeightValue = weightInKg.divide(divisor.weightInKg, NumberUtil.MC);
    return new Weight(newWeightValue, Weight.Unit.KILOGRAM);
}
public boolean isZero()
{
    if (weightInKg.signum() == 0)
        return true;
    return false;
}
public boolean isEqual(final Weight another)
{
    if (weightInKg.compareTo(another.weightInKg) == 0)
        return true;
    return false;
}
}

实例化卷时，用户被迫显式提供单位。

Volume myCubicMeter, myCubicInch;
myCubicMeter = new Volume("1", Volume.Unit.CUBIC_METER);
myCubicInch = new Volume("1", Volume.Unit.CUBIC_INCH);

我试图实现的是一个抽象类，它将实现所有方法并强制子类使用值实现枚举。正确的方法是什么？

Answer 1

在 Java 中，枚举是提供的Enum类的子类。

你不能给它们一个共同的抽象祖先，也不能给它们子类化。如果你真的想保留一组枚举中用编译时常量引用你的单位的商品，那么你做不到。

如果您放弃使用枚举并可能将它们声明为普通类，那么您可以像其他所有内容一样自由地执行此操作，例如

class VolumeUnit extends AbstractUnit {
  public static final VolumeUnit CUBIC_METER = new VolumeUnit(params);
  ..
  VolumeUnit(..) {
    ..
  }
}