java Java将父级转换为子级？
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Java cast parent to child?
提问by Kyle V.
Here is my code:
这是我的代码：
for (DrawableEntity entity : drawableEntityList) {
if (entity instanceof Beam) {
(Beam) entity.age += timeElapsed;
}
else if (entity instanceof Block) {
}
}
Basically drawableEntityListis a Vectorof DrawableEntitys, and I want to iterate through everything in the Vector. Then depending on if they are subclass Beamor subclass BlockI want to do something different.
基本上drawableEntityList是Vector的DrawableEntitys，我通过在一切要迭代Vector。然后取决于它们是子类Beam还是子类，Block我想做一些不同的事情。
The problem is that I'm trying to change a variable that only the subclasses have, I figured I could cast with (Beam) but it doesn't work.
问题是我正在尝试更改只有子类具有的变量，我想我可以使用 (Beam) 进行转换，但它不起作用。
Is it not possible to cast a parent class to a child class?
不能将父类转换为子类吗？
回答by Bala R
Your casting syntax is not right.
您的转换语法不正确。
Try this
试试这个
if (entity instanceof Beam) {
((Beam) entity).age += timeElapsed;
}
else if (entity instanceof Block) {
}
回答by Alexandr
Notes: Beware of instanceofoperator
注意事项：小心instanceof操作员
