Java理解继承:从父类获取getter和setter方法

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英文:

Java understanding inheritance: getter and setter from parents class

问题

以下是翻译好的内容:

父类:

class MyPoint {
    public int x, y;

    MyPoint() {
        x = 0;
        y = 0;
    }

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

    MyPoint(MyPoint myPoint) {
        x = myPoint.x;
        y = myPoint.y;
    }

    public int getX() {
        return x;
    }

    public int getY() {
        return y;
    }

    public void setX(int x) {
        if (x > 0) {
            this.x = x;
        }
    }

    public void setY(int y) {
        if (y > 0) {
            this.y = y;
        }
    }

    public String toString() {
        return "(" + x + ", " + y + ")";
    }
}

子类:

class MySubLine extends MyPoint {
    int x, y, x1, y1;
    MyPoint endPoint;

    public MySubLine() {
        super();
        x1 = 0;
        y1 = 0;
    }

    public MySubLine(int x, int y, int x1, int y1) {
        super(x, y);
        this.x = x;
        this.y = y;
        this.x1 = x1;
        this.y1 = y1;
    }

    public MySubLine(MyPoint p1, MyPoint p2) {
        super(p1.x, p1.y);
        x = p1.x;
        y = p2.y;
        x1 = p2.x;
        y1 = p2.y;
    }

    public int getEndX() {
        return x1;
    }

    public int getEndY() {
        return y1;
    }

    public void setEndX(int x) {
        if (x > 0) {
            this.x1 = x;
        }
    }

    public void setEndY(int y) {
        if (y > 0) {
            this.y1 = y;
        }
    }

    public double getLength() {
        return Math.sqrt(Math.pow((x1 - x), 2) + Math.pow((y1 - y), 2));
    }

    public String toString() {
        return "(" + x + ", " + y + ") to (" + x1 + ", " + y1 + ")";
    }
}

测试案例:

MySubLine line = new MySubLine();
line.setX(40); line.setY(50);
System.out.println(line);

运行该测试案例在主 Java 文件中,得到的结果是 (0, 0) to (0, 0),然而预期的结果是 (40, 50) to (0, 0)

为什么我的 setter 方法没有触发?

将不相关的部分删除,只返回了翻译好的内容,如有需要,请随时询问。

英文:

Java beginner again. I am trying to understand how inheritance works and I think I kind of got it, but my code does not work as I expected and hard to figure out the reason why.

The problem is my getter and setter methods from the parents class. It doesn't seem that my code is calling them as I expect.

Here is my parent class:

class MyPoint {
public int x, y;
MyPoint() {
x = 0;
y = 0;
}
MyPoint(int x, int y) {
this.x = x;
this.y = y;
}
MyPoint(MyPoint myPoint) {
x = myPoint.x;
y = myPoint.y;
}
public int getX() {
return x;
}
public int getY() {
return y;
}
public void setX(int x) {
if (x > 0) {
this.x = x;
}
}
public void setY(int y) {
if (y > 0) {
this.y = y;
}
}
public String toString() {
return "(" + x + ", " + y + ")";
}
}

And the child class:

class MySubLine extends MyPoint {
int x, y, x1, y1;
MyPoint endPoint;
public MySubLine() {
super();
x1 = 0;
y1 = 0;
}
public MySubLine(int x, int y, int x1, int y1) {
super(x, y);
this.x = x;
this.y = y;
this.x1 = x1;
this.y1 = y1;
}
public MySubLine(MyPoint p1, MyPoint p2) {
super(p1.x, p1.y);
x = p1.x;
y = p2.y;
x1 = p2.x;
y1 = p2.y;
}
public int getEndX() {
return x1;
}
public int getEndY() {
return y1;
}
public void setEndX(int x) {
if (x > 0) {
this.x1 = x;
}
}
public void setEndY(int y) {
if (y > 0) {
this.y1 = y;
}
}
public double getLength() {
return Math.sqrt(Math.pow((x1 - x), 2) + Math.pow((y1 - y), 2));
}
public String toString() {
return "(" + x + ", " + y + ") to (" + x1 + ", " + y1 + ")";
}
}

And when I try to run a test case of

MySubLine line = new MySubLine();
line.setX(40); line.setY(50);
System.out.println(line);

in my main Java file, the result I am getting is (0, 0) to (0, 0) while the expected result is (40, 50) to (0, 0).

Why arent my setter methods triggered?

Any help will be appreciated!

答案1

得分: 3

你在子类中重新声明了x和y,因此它们遮盖了超类中同名的变量。

line.setX(40);

这将调用超类中的方法,从而在MyPoint中设置x。

在子类中:

public String toString() {
    return "(" + x + ", " + y + ") 到 (" + x1 + ", " + y1 + ")";
}

这将访问MySubLine中未被修改的x和y。

解决方案:从MySubLine中移除x和y作为实例成员。

英文:

You have declared x and y again in your subclass so they overshadow the variables with the same names in the super class

line.setX(40)

This will call the method in the superclass and thus setting x in MyPoint

In subclass

public String toString() {
return "(" + x + ", " + y + ") to (" + x1 + ", " + y1 + ")";
}

this will access x and y in MySubLine which have not been modified.

Solution: remove x and y as instance members from MySubLine

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  • 本文由 发表于 2020年4月10日 21:14:20
  • 转载请务必保留本文链接:https://go.coder-hub.com/61141047.html
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