添加2个BigDecimal值 [英] adding 2 BigDecimal values

问题描述

class Point {

  BigDecimal x;
  BigDecimal y;

  Point(double px, double py) {
    x = new BigDecimal(px);
    y = new BigDecimal(py);
  }

  void addFiveToCoordinate(String what) {
    if (what.equals("x")) {
      BigDecimal z = new BigDecimal(5);
      x.add(z);
    }
  }

  void show() {
    System.out.print("\nx: " + getX() + "\ny: " + getY());
  }

  public BigDecimal getX() {
    return x;
  }

  public BigDecimal getY() {
    return y;
  }

  public static void main(String[] args) {
    Point p = new Point(1.0, 1.0);
    p.addFiveToCoordinate("x");
    p.show();
  }
}

好的，我想添加2个BigDecimal值.我正在使用带有double的构造函数(因为我认为这是可能的-文档中有一个选项).如果我在主类中使用它，我会得到:

Ok, I would like to add 2 BigDecimal values. I'm using constructor with doubles(cause I think that it's possible - there is a option in documentation). If I use it in main class, I get this:

x: 1
y: 1

当我使用System.out.print显示我的z变量时，我得到了:

When I use System.out.print to show my z variable i get this:

z: 5

推荐答案

BigDecimal是不可变的.每个操作都会返回一个包含操作结果的新实例:

BigDecimal is immutable. Every operation returns a new instance containing the result of the operation:

 BigDecimal sum = x.add(y);

如果您想更改x，则必须这样做

If you want x to change, you thus have to do

x = x.add(y);

阅读 javadoc 确实有助于理解类及其方法如何工作.

Reading the javadoc really helps understanding how a class and its methods work.

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