java - 二次公式程序 - 出现 NaN 错误

Question

我不确定我的代码中做错了什么，但我无法让它正常运行...测试器不断返回 NaN 而不是预期的结果。本练习的目标是打印二次方程的所有实数解。 Solution1 应返回较小的解决方案，solution2 应返回较小的解决方案。这是我的类(class)。

   public class QuadraticEquation
   {
    private int a;
    private int b;
    private int c;
    private boolean hasSolutions;
    private double discriminant = (b * b) - (4 * a * c);
    private double solution1;
    private double solution2;
   /**
 * Constructs a quadratic equation
 * @param a coefficient a 
 * @param b coefficient b
 * @param c coefficient c
 */

    public QuadraticEquation(int a, int b, int c)
    {
        a = a;
        b = b;
        c = c;
    }
     /**
 * Checks if there is a solution
 * @return true if there is a real solution
 */

    public boolean hasSolutions()
    {
        if(discriminant < 0)
            hasSolutions = false;
        else
            hasSolutions = true;
        return hasSolutions;
    }
    /**
  * Returns first solution
  * @return first solution
  */

    public double getSolution1()
    {
        if(hasSolutions)
        {
            if((-b + Math.sqrt(discriminant) / (2 * a)) < (-b - Math.sqrt(discriminant) / (2 * a)))
                solution1 = (-b + Math.sqrt(discriminant) / (2 * a));
            else
                solution1 = (-b - Math.sqrt(discriminant) / (2 * a));
        }
            return solution1;
    }
    /**
    * Returns second solution
    * @return second solution
    */  

    public double getSolution2()
    {
        if(hasSolutions)
        {
            if((-b + Math.sqrt(discriminant) / (2 * a)) > (-b - Math.sqrt(discriminant) / (2 * a)))
                solution2 = (-b + Math.sqrt(discriminant) / (2 * a));
            else
                solution2 = (-b - Math.sqrt(discriminant) / (2 * a));
        }
            return solution2;
    }

  }

这是我的测试仪:

    public class QuadraticEquationTester
    {
    public static void main(String[] args)
      {
          QuadraticEquation equation = new QuadraticEquation(2, 2, -4);
          System.out.println(equation.hasSolutions());
          System.out.println("Expected: true");
          System.out.println(equation.getSolution1());
          System.out.println("Expected: -2");
          System.out.println(equation.getSolution2());
          System.out.println("Expected: 1");

          QuadraticEquation equation2 = new QuadraticEquation(2, 2, 4);
          System.out.println("\n" + equation2.hasSolutions());
          System.out.println("Expected: false");
          System.out.println(equation2.getSolution1());
          System.out.println("Expected: 0");
          System.out.println(equation2.getSolution2());
          System.out.println("Expected: 0");
        }
     }

非常感谢! :)

Answer 1

1. 您正在类上下文的对象初始化部分中计算判别式，该部分使用默认值a、b 和c 进行计算。在初始化 a,b 和 c

之前不要计算

2. 您在构造函数方法中隐藏了变量，因为 a、b、c 是参数字段。使用这个:

   public QuadraticEquation(int a, int b, int c)
   {
     this.a = a;
     this.b = b;
     this.c = c;
   }
   

3. NaN 通过零除以零等运算进行浮点计算。所以找出上述修复后是否仍然发生这种情况。