使 Class 不可变

Question

我正在学习不可变对象。我必须让以下 class 不可变。我做对了吗？

import java.awt.Point;
public class MyImmutablePoint {
    Point point;

    public MyImmutablePoint(Point point) {
        super();
        this.point = point;
    }

    public MyImmutablePoint() {
        this (new Point (0,0));
    }

    public Point getPoint() {
        return point;
    }

    public void setPoint(Point point) {
        this.point = point
    }
}

"Immutable" Class:

public final class MyImmutablePoint {
    private final Point point;

    public MyImmutablePoint(Point point) {
        this.point = point;
    }

    public MyImmutablePoint() {
        this (new Point (0,0));
    }

    public Point getPoint() {
        return point;
    }   
}

虽然我不确定 toString 方法。也许返回一个像 Point 这样的对象也可以像数组一样被修改但不确定

Answer 1

不，它不是一成不变的。 Point 仍然可以被 MyImmutablePoint 的创建者修改。例如：

    Point point = new Point(1, 1);
    MyImmutablePoint immutablePoint = new MyImmutablePoint(point);
    point.setLocation(0, 0);

Answer 2

没有

final Point p = new Point(0,0);
final ImmutablePoint ip = new ImmutablePoint(p);

两个例子：

//change the original Point passed in
p.x = 10
//use the getter and change the Point
ip.getPoint().x = 10

所以，首先你需要创建一个防御副本 Point 在构造函数中：

public MyImmutablePoint(Point point) {
    this.point = new Point(point);
}

然后您需要创建从 getter:

返回的 Point 的防御副本

public Point getPoint() {
    return new Point(point);
}

这一切让我建议最好不要公开内部 point：

public final class MyImmutablePoint {

    private final Point point;

    public MyImmutablePoint(Point point) {
        this.point = new Point(point);
    }

    public MyImmutablePoint() {
        this.point = new Point (0,0);
    }

    public int getX() {
        return point.x;
    }

    public int getY() {
        return point.y;
    }
}

进一步格式化您的代码并订购您的会员。

使 Class 不可变

Making a Class Immutable

java

immutability

没有