java 处理Float和Double时要小心陷阱

ゝ一纸荒年。 2024-02-18 18:18 17阅读 0赞

Float和Double包括float和double，有

NEGATIVE_INFINITY
    -0.0
    0
    0.0
    POSITIVE_INFINITY

和  
`NaN`  
与NaN进行比较，结果都是false。  
所以尽量把“targeted执行的语句”放在确定的判断中，并且该判断返回true（因为NaN参与的判断一律返回false）

public employee(float monthly_salary)
    {
      if (monthly_salary >= 0.0)
      {
        this.yearly_salary = 12.0 * monthly_salary; // targeted执行的语句
      }
      else throw IllegalArgumentException("illegal monthly salary");
    }

而下面的代码因为没有考虑monthly\_salary等于NaN的情况，而不正确：

public employee(float monthly_salary)
    {
      if (monthly_salary < 0.0)
        throw IllegalArgumentException("illegal monthly salary");
      this.yearly_salary = 12.0 * monthly_salary; // targeted执行的语句在外面
    }

参考：  
[http://blog.csdn.net/jierui001/article/details/3278382][http_blog.csdn.net_jierui001_article_details_3278382]  
除此以外，在对浮点型进行处理时，可以参照Princeton的代码：

public Point2D(double x, double y) {
            if (Double.isInfinite(x) || Double.isInfinite(y))
                throw new IllegalArgumentException("Coordinates must be finite");
            if (Double.isNaN(x) || Double.isNaN(y))
                throw new IllegalArgumentException("Coordinates cannot be NaN");
            if (x == 0.0) this.x = 0.0;  // convert -0.0 to +0.0
            else          this.x = x;
    
            if (y == 0.0) this.y = 0.0;  // convert -0.0 to +0.0
            else          this.y = y;
        }

以及

public Interval1D(double min, double max) {
            if (Double.isInfinite(min) || Double.isInfinite(max))
                throw new IllegalArgumentException("Endpoints must be finite");
            if (Double.isNaN(min) || Double.isNaN(max))
                throw new IllegalArgumentException("Endpoints cannot be NaN");
    
            // convert -0.0 to +0.0
            if (min == 0.0) min = 0.0;
            if (max == 0.0) max = 0.0;
    
            if (min <= max) {
                this.min = min;
                this.max = max;
            }
            else throw new IllegalArgumentException("Illegal interval");
        }

参考：  
[https://algs4.cs.princeton.edu/12oop/][https_algs4.cs.princeton.edu_12oop]

[http_blog.csdn.net_jierui001_article_details_3278382]: http://blog.csdn.net/jierui001/article/details/3278382
[https_algs4.cs.princeton.edu_12oop]: https://algs4.cs.princeton.edu/12oop/