Java Rounding（双）

Question

double y1 = 0;  
double y2 = 0;  
double i = 0.025;  
double n = 2;  
double h1 = 2000; 
double h2 = 4000; 

y1 = Math.pow((1 + i), n) * h1;
y2 = Math.pow((1 + i), n) * h2;
double result =  y1 + y2;
System.out.println(result);

我希望结果为＆＃34; 6303.749999999999＆＃34;但它给了我＆＃34; 6303.75＆＃34;。我该如何解决？

Answer 1

正确的结果应该是（并且是） 6303.750000000000017069679003611781820568916563219777423023367655509563911228609889292329171439632773399353027343750000

尝试看一下BigDecimal类。

    BigDecimal i = new BigDecimal(0.025);
    int n = 2;
    BigDecimal h1 = new BigDecimal(2000);
    BigDecimal h2 = new BigDecimal(4000);

    BigDecimal y1 = ((BigDecimal.ONE.add(i)).pow(n)).multiply(h1);
    BigDecimal y2 = ((BigDecimal.ONE.add(i)).pow(n)).multiply(h2);
    BigDecimal result =  y1.add(y2);

    System.out.println(result.toEngineeringString());

Answer 2

问题是您计算值6303.75。如果您添加一个语句，从变量0.000000000001中减去值result，那么您将获得预期值6303.749999999999。

以下代码更改演示了如何计算6303.749999999999：

public static void main(String[] args){

    double y1 = 0;  
    double y2 = 0;  
    double i = 0.025;  
    double n = 2;  
    double h1 = 2000; 
    double h2 = 4000; 

    y1 = Math.pow((1 + i), n) * h1;
    y2 = Math.pow((1 + i), n) * h2;
    double result =  y1 + y2;
    result -= (double)0.000000000001; // this line is the key to calculating the expected result
    System.out.println(result);
}

<强>输出：

  

6303.749999999999