具有默认值的抽象类

Question

我试图定义一个抽象的Range类,它将作为许多范围类的基本实现.预期用途与此问题无关,但到目前为止,我有:

/**
 * Abstract generic utility class for handling ranges
 */
public abstract class Range<T extends Number> {

  // Variables to hold the range configuration
  private T start;
  private T stop;
  private T step;

  /**
   * Constructs a range by defining it's limits and step size.
   *
   * @param start The beginning of the range.
   * @param stop The end of the range.
   * @param step The stepping
   */
  public Range(T start, T stop, T step) {
    this.start = start;
    this.stop = stop;
    this.step = step;
  }
}

现在我想添加一个构造函数,只需要start和stop,并设置一个默认的步长值1,无论是什么实现Number T(例如,如果T是Integer [one]有值1,如果T是Long [one]有值1L,依此类推).我想要像:

protected Range(T start, T stop) {
  this(start, stop, [one]);
}

但我无法弄清楚如何设定价值[one].由于Java对我来说还是一个新手,我尝试过:

private static final T one = 1;

哪个不起作用,因为T显然是在实例化中定义的Range.this.我也尝试过:

protected static abstract T getOne();

这也不起作用,因为T在Range.thisplus 的实例化中定义static并且abstract不能一起工作.

我需要一些方法来扩展类以强制定义值,[one]无论实现什么实现Number Range.

最后我还想将零值设置为默认开始,这样我得到一个如下所示的构造函数:

protected Range(T stop) {
  this([zero], stop, [one]);
}

Answer 1

一种解决方案是询问子类使用的默认步骤:

public abstract class Range<T extends Number> {

    private T start;
    private T stop;
    private T step;

    public Range(T start, T stop, T step) {
        this.start = start;
        this.stop = stop;
        this.step = step;
    }

    protected Range(T start, T stop) {
        this.start = start;
        this.stop = stop;
        this.step = getDefaultStep();
    }

    protected abstract T getDefaultStep();

}

public class IntegerRange extends Range<Integer> {

    public IntegerRange(Integer start, Integer stop, Integer step) {
        super(start, stop, step);
    }

    public IntegerRange(Integer start, Integer stop) {
        super(start, stop);
    }

    @Override
    protected Integer getDefaultStep() {
        return 1;
    }

}

public class DoubleRange extends Range<Double> {

    public DoubleRange(Double start, Double stop, Double step) {
        super(start, stop, step);
    }

    public DoubleRange(Double start, Double stop) {
        super(start, stop);
    }

    @Override
    protected Double getDefaultStep() {
        return 1d;
    }

}

Answer 2

您可以使用此实现:

protected Range(T start, T stop) {
  this(start, stop, (T) (new Integer(1)));
}