为什么我不能用(Point2d.Double)键入castJAVA
我有下面的代码片段-它不起作用为什么我不能用(Point2d.Double)键入castJAVA,java,casting,classcastexception,Java,Casting,Classcastexception,我有下面的代码片段-它不起作用 private void startAddingTrackPointValue() { Set<Point2D.Double> keySet = this.trackPointList.keySet(); Point2D.Double[] keys = (Point2D.Double[]) keySet.toArray(); for(int i = 0; i < keys.length; i
private void startAddingTrackPointValue()
{
Set<Point2D.Double> keySet = this.trackPointList.keySet();
Point2D.Double[] keys = (Point2D.Double[]) keySet.toArray();
for(int i = 0; i < keys.length; i++)
{
System.out.println(keys[i]);
}
}
private void startAddingTrackPointValue()
{
Set keySet=this.trackPointList.keySet();
Point2D.Double[]keys=(Point2D.Double[])keySet.toArray();
for(int i=0;i
生成的异常为,此
Exception in thread "main" java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to [Ljava.awt.geom.Point2D$Double;
at SegmentFactory.startAddingTrackPointValue(SegmentFactory.java:170)
at SegmentFactory.<init>(SegmentFactory.java:44)
at TestClass.main(TestClass.java:8)
线程“main”java.lang.ClassCastException:[Ljava.lang.Object;中的异常不能转换为[Ljava.awt.geom.Point2D$Double;
在SegmentFactory.startAddingTrackPointValue(SegmentFactory.java:170)处
在SegmentFactory。(SegmentFactory.java:44)
位于TestClass.main(TestClass.java:8)
但是这个很好用,如果我这样做
private void startAddingTrackPointValue()
{
Set<Point2D.Double> keySet = this.trackPointList.keySet();
Object[] keys = (Object[]) keySet.toArray();
for(int i = 0; i < keys.length; i++)
{
System.out.println(keys[i]);
}
}
private void startAddingTrackPointValue()
{
Set keySet=this.trackPointList.keySet();
Object[]keys=(Object[])keySet.toArray();
for(int i=0;i
问题是,为什么我不能用Point2D.Double[]进行类型转换?因为“Object[]”不是“Point2D.Double[]”的实例
这两种方法都不起作用:
Point2D.Double[] = (Point2D.Double[])new Object[0]; // this is essentially what your code is doing
Point2D.Double = (Point2D.Double)new Object();
改为这样做:
Point2D.Double[] keys = (Point2D.Double[]) keySet.toArray(new Point2D.Double[keySet.size()]);
将键入的数组传递给
toArray()
:
部分正确,但是.toArray参数()中需要“new”关键字。Thanks@SkeetOverFlow-对不起,我打字太快了。一个方便的构造函数会很好。
Point2D.Double[] keys = keySet.toArray(new Point2D.Double[keySet.size()]);