java中的私有实例和getter可见性

Question

并感谢每个人修复格式等,这里全新

我最近开始学习java,在一次练习中发生了一个问题,抱歉,如果我错过了发布规则:

从一个MyPoint到另一个Mypoint计算距离,我决定使用用于MyPoint吸气另一个因为x和y为另一个应该是私有的,并且不能在点操作(another.x another.y)中使用;

public class MyPoint {
    private int x;
    private int y;                   

    public int getX() {             
        return x;
    }

    public int getY() {            
        return y;
    } 

    public double distance(MyPoint another) { 
        int xDiff = this.x - another.getX();           //getter
        int yDiff = this.y - another.getY();          // getter

        return Math.sqrt(xDiff * xDiff + yDiff * yDiff);
    }
}

public class TestMyPoint {
    public static void main(String[] args) {
        MyPoint a = new MyPoint(3,0);
        MyPoint b = new MyPoint(0,4);

        System.out.println(a.distance(b));  // this works fine;
    }
}

但是,如果我回到代码并将another.getX()更改为another.x,代码仍然有效.和y相同.

public class MyPoint {
    private int x;
    private int y;              

    public MyPoint(int x, int y) {
        this.x = x;
        this.y = y;
    }     

    public int getX() {             
        return x;
    }
    public int getY() {            
        return y;
    } 

    public double distance(MyPoint another) { 
        int xDiff = this.x - another.x;                         //no getter
        int yDiff = this.y - another.y;                         //no getter

        return Math.sqrt(xDiff * xDiff + yDiff * yDiff);
    }
}


public class TestMyPoint {
    public static void main(String[] args) {
        MyPoint a = new MyPoint(3,0);
        MyPoint b = new MyPoint(0,4);

        System.out.println(a.distance(b));  // this still works fine;
    }
}

我认为,因为另一个是MyPoint类,而实例x和y是私有的,所以.x和.y无法工作,这就是设置私有实例并使用getter的重点.

我错过了什么？

Answer 1

private表示只能从内部访问字段MyPoint.这并不意味着他们只能从与访问同一个实例的MyPoint.这对于那些在"其他"的情况下,尤其是操作方法完全合法的equals,并compareTo在同一类的其他实例来访问私有状态.