Java类强制转换异常java.awt.geom.Path2D.Double [英] Java Class Cast Exception java.awt.geom.Path2D.Double

问题描述

在尝试实现AffineTransform时，我一直在收到此类强制转换异常.

I've been getting this class cast exception when trying to to implement an AffineTransform.

调用AffineTransform:

Call to AffineTransform:

public Shape moveToAndRotate(double x, double y, double theta)
{
    double cx = getBounds2D().getCenterX();
    double cy = getBounds2D().getCenterY();

    at.translate(cx, cy);
    at.translate(x, y);
    at.rotate(Math.toRadians(theta));
    at.translate(-cx, -cy);
    return at.createTransformedShape(yingYang);
}

这位于自定义形状类(YingYang)中.

This is resides in a custom shape class (YingYang).

public class YingYang implements Shape
{
    private Area yingYang = new Area();
    private AffineTransform at = new AffineTransform();
    ...
}

每当我打电话时，当我尝试从绘图面板或在其自身的类中将其投射回盈阳时，都会发生类转换异常(如果我将返回类型更改为盈阳.

When ever I make a call I get a class cast exception when I try to cast this back to a YingYang either from the drawing panel or within the class it self (if I change the return type to YingYang.

我这样拨打电话:

YingYang newShape = (YingYang) shape.moveToAndRotate(newLoc1.x, newLoc1.y, theta);

这是错误:

java.lang.ClassCastException:java.awt.geom.Path2D $ Double无法转换为Animation.YingYang

java.lang.ClassCastException: java.awt.geom.Path2D$Double cannot be cast to Animation.YingYang

自从颖阳实现了形状成形以来，任何想法都认为我完全不必铸造这种形状.我错过了一个关键概念吗?

Any ideas since YingYang implements shape one would think that I shouldn't have to cast this at all. Am I missing a key concept?

推荐答案

您将收到一个类强制转换异常，因为您只能向上继承树.意思是阴阳是一个形状，但形状不一定是阴阳. createTransformedShape返回的Path2D是Shape.但是那个Shape不是阴阳.

You are getting a class cast exception because you can only go up the inheritance tree. Meaning YinYang is a Shape but a Shape isnt necessarily a YinYang. createTransformedShape is returning a Path2D which is a Shape. But that Shape is not a YinYang.

您可以保留变量yinYang = new Area();在您的YinYang班级内部，或者让您的YinYang扩展该区域.

You could either keep the variable yinYang = new Area(); inside your YinYang class or make your YinYang extend the area.

所以阴阳区->有一个区域.应该是阴阳->是一个区域

So intead of YinYang -> has an Area. It would be YinYang -> is an Area

如果确实需要打开扩展继承，则可以实现形状并实现所有方法以使用yinYang变量.

If you really need to leave the extends inheritance open you can implement a shape and implement all the methods to go to the yinYang variable.

然后创建一个类似于以下内容的构造函数

Then make a constructor like the following

private class YinYang extends Area {
    public YinYang(Shape shape) {
        super(shape);
    }
}

public Shape moveToAndRotate(double x, double y, double theta)
{
    double cx = getBounds2D().getCenterX();
    double cy = getBounds2D().getCenterY();

    at.translate(cx, cy);
    at.translate(x, y);
    at.rotate(Math.toRadians(theta));
    at.translate(-cx, -cy);
    return at.createTransformedShape(yingYang);
}

YingYang shape = new YingYang(shape.moveToAndRotate(newLoc1.x, newLoc1.y, theta));

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