Question

1- long xValue = someValue;

2- long yValue = someValue;

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

这行代码给出了以下异常：

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

更新：

代码：

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包含双值as the passed chart has Number type，但是getYvalue（）返回long，这就是程序在运行时因该异常而崩溃的原因，但是当我在线转换为什么转换不成功时。我认为编译器看到的类型已经很长了！

Answer 1

这是不可能的

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

这三行中都不能产生java.lang.ClassCastException

假设someValues为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 2

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

long otherTolalValue = xValue - yValue;

但请记住，你会失去精确度。

Answer 3

我真的不明白为什么你的代码失败了，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

据推测，someValue是double。要将其分配给long，您需要将其投射：

long xValue = (long) someValue;

Java转换为double to long异常

4 个答案: