java - Java 将 double 转换为 long 异常

Question

1- 长 xValue = someValue;

2- 长 yValue = someValue;

3- long otherTolalValue = (long)(xValue - yValue);

那行代码给了我以下异常：

java.lang.ClassCastException: java.lang.Double cannot be cast to java.lang.Long.

• 更新 ：

代码段：

StackedBarChart<String,Number> sbc = new StackedBarChart<String,Number>();

XYChart.Series<String, Number> series = new XYChart.Series<String, Long>();
series.getData.add(new XYChart.Data<String, Number>("X1",150));
series.getData.add(new XYChart.Data<String, Number>("X2",50));
sbc.getData.add(series);
long dif = getDif(sbc);

long getDif(XYChart barChart){
XYChart.Series series = (XYChart.Series).getData().get(0);
// X1 at zero position i dont have to use iIterator now.
XYChart.Data<String, Long> seriesX1Data = series.getData().get(0);
XYChart.Data<String, Long> seriesX2Data = series.getData().get(1);

long x1Value = seriesX1Data.getYValue();
long x2Value = seriesX1Data.getYValue();
// line - 3 - exception on the next line
// -4- long value = (x1Value) - (x2Value);
long value = (long)(x1Value) - (long)(x2Value);
return value;
}

• 调试后我发现了。

seriesX1Data,seriesX2Data包含双精度值as the passed chart has Number type，但 getYvalue() 返回 long，这就是为什么程序在运行时崩溃并出现该异常，但是当我在线投射时，为什么投射不成功。我认为编译器看到该类型已经很长了！

Answer 1

long xValue = (long)someValue;
// or : 
long yValue = new Double(someValue).longValue();

long otherTolalValue = xValue - yValue;

但请记住，您将失去精度。

Answer 2

不可能

long xValue = someValue;
long yValue = someValue;
long otherTolalValue = (long)(xValue - yValue);

3 行都不能产生 java.lang.ClassCastException

假设 someValues 是 Double，

Double someValue = 0.0;

它会给出编译错误：类型不匹配：无法将 Double 转换为 long

Answer 3

我真的不明白为什么您的代码会失败，但以下也可以正常工作。

    public class CastingDoubleToLongTest {

      @Test
      public void testCast(){
        double xValue = 12.457;
        double yValue = 9.14;

        long diff = new Double(xValue - yValue).longValue();

        Assert.assertEquals(3, diff);
      }
   }

Answer 4

大概someValue是一个double。要将其分配给long您需要转换它：

long xValue = (long) someValue;