Java 中 Vector2d 类中的旋转 [英] Rotation in a Vector2d class in Java

问题描述

我已经为此工作了一个小时，只是无法理解.

I've been working on this for one hour, just can't get it.

我有一个 Vector2d 类:

I have a Vector2d class:

public class Vector2d
{
    public double x = 0.0;
    public double y = 0.0;

    ....
}

这个向量类有一个 rotate() 方法，这给我带来了麻烦.

This vector class has a rotate() method which is causing me trouble.

第一个片段似乎使 x 和 y 值越来越小.第二个工作得很好！我在这里遗漏了一些简单的东西吗?

The first snippet seems to make the x and y values smaller and smaller. The second one works just fine! Am I missing something simple here?

public void rotate(double n)
{
    this.x = (this.x * Math.cos(n)) - (this.y * Math.sin(n));
    this.y = (this.x * Math.sin(n)) + (this.y * Math.cos(n));
}

这有效:

public void rotate(double n)
{
    double rx = (this.x * Math.cos(n)) - (this.y * Math.sin(n));
    double ry = (this.x * Math.sin(n)) + (this.y * Math.cos(n));
    x = rx;
    y = ry;
}

我就是看不出有什么不同

I just can't spot any difference there

推荐答案

第一行设置 this.x 的值，当你真正想要的是原始值时，第二行使用this.x 的值.第二个版本工作正常，因为您没有更改 this.x.

The first line sets the value of this.x which is then used in the second line when what you really want is the original value of this.x. The second version works fine because you don't alter this.x.

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