Java中为Rect类添加宽高合法性控制的实现方法

我创建了一个仅包含矩形属性的Rect类，希望实现以下逻辑：width和length必须为大于0的整数，若传入负数则取其绝对值。已有多年未使用Java，相关经验有限，不清楚应在何处编写对应代码，附上当前Rect类代码：

public class Rect {

    int x;
    int y;
    int width;
    int length;

    public int getPerimeter() {
        return (2 * width) + (2 * length);
    }

    public int getArea() {
        return width * length;
    }

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

    public void changeSize(int n) {
        this.width = n;
        this.length = n;
    }

    public void print(int area, int perimeter) {
        System.out.printf("X: %d\n", this.x);
        System.out.printf("Y: %d\n", this.y);
        System.out.printf("Length: %d\n", this.width);
        System.out.printf("Width: %d\n", this.length);
        System.out.printf("Area: %d\n", area);
        System.out.printf("Perimeter: %d", perimeter);
    }

    public static void main(String[] args) {
        Rect r1 = new Rect();
        r1.length = 1;
        r1.width = 2;
        r1.x = 3;
        r1.y = 4;

        //test here
        int area = r1.getArea();
        int perimeter = r1.getPerimeter();

        r1.print(area, perimeter);

    }
}

要实现width和length的合法性校验，核心是封装成员变量，通过Getter/Setter方法控制属性赋值逻辑，避免外部直接操作成员变量。具体实现步骤如下：

1. 私有化成员变量 #

将所有属性设为private，禁止外部直接修改：

private int x;
private int y;
private int width;
private int length;

2. 编写带校验逻辑的Setter方法 #

为width和length编写Setter方法，在方法内处理负数取绝对值，同时确保值大于0（若传入0则默认设为1，可根据需求调整）：

public void setWidth(int width) {
    this.width = Math.abs(width);
    // 保证值大于0，避免传入0的情况
    if (this.width == 0) {
        this.width = 1;
    }
}

public void setLength(int length) {
    this.length = Math.abs(length);
    if (this.length == 0) {
        this.length = 1;
    }
}

同时为x、y编写普通Setter方法（无需校验逻辑），并为所有属性添加Getter方法：

public int getX() {
    return x;
}

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

public int getY() {
    return y;
}

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

public int getWidth() {
    return width;
}

public int getLength() {
    return length;
}

3. 修改现有方法与初始化逻辑 #

• 调整changeSize方法，使用Setter而非直接赋值：

public void changeSize(int n) {
    setWidth(n);
    setLength(n);
}

• 修正print方法的输出错误（原代码将width和length的输出搞反了）：

public void print(int area, int perimeter) {
    System.out.printf("X: %d\n", this.x);
    System.out.printf("Y: %d\n", this.y);
    System.out.printf("Length: %d\n", this.length);
    System.out.printf("Width: %d\n", this.width);
    System.out.printf("Area: %d\n", area);
    System.out.printf("Perimeter: %d", perimeter);
}

• 修改main方法的初始化代码，使用Setter设置属性：

public static void main(String[] args) {
    Rect r1 = new Rect();
    r1.setLength(1);
    r1.setWidth(2);
    r1.setX(3);
    r1.setY(4);

    // 测试负数输入
    r1.setWidth(-5);
    r1.setLength(-3);

    int area = r1.getArea();
    int perimeter = r1.getPerimeter();

    r1.print(area, perimeter);
}

4. 可选：添加带参构造方法 #

添加构造方法，在创建对象时直接完成属性的校验初始化：

public Rect(int x, int y, int width, int length) {
    setX(x);
    setY(y);
    setWidth(width);
    setLength(length);
}

使用示例：

Rect r1 = new Rect(3, 4, 2, 1);

完整修改后的代码 #

public class Rect {

    private int x;
    private int y;
    private int width;
    private int length;

    // 无参构造
    public Rect() {}

    // 带参构造
    public Rect(int x, int y, int width, int length) {
        setX(x);
        setY(y);
        setWidth(width);
        setLength(length);
    }

    public int getPerimeter() {
        return (2 * width) + (2 * length);
    }

    public int getArea() {
        return width * length;
    }

    public void move(int x, int y) {
        setX(x);
        setY(y);
    }

    public void changeSize(int n) {
        setWidth(n);
        setLength(n);
    }

    public void print(int area, int perimeter) {
        System.out.printf("X: %d\n", this.x);
        System.out.printf("Y: %d\n", this.y);
        System.out.printf("Length: %d\n", this.length);
        System.out.printf("Width: %d\n", this.width);
        System.out.printf("Area: %d\n", area);
        System.out.printf("Perimeter: %d", perimeter);
    }

    // Getter和Setter方法
    public int getX() {
        return x;
    }

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

    public int getY() {
        return y;
    }

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

    public int getWidth() {
        return width;
    }

    public void setWidth(int width) {
        this.width = Math.abs(width);
        if (this.width == 0) {
            this.width = 1;
        }
    }

    public int getLength() {
        return length;
    }

    public void setLength(int length) {
        this.length = Math.abs(length);
        if (this.length == 0) {
            this.length = 1;
        }
    }

    public static void main(String[] args) {
        Rect r1 = new Rect();
        r1.setLength(1);
        r1.setWidth(2);
        r1.setX(3);
        r1.setY(4);

        // 测试负数输入
        r1.setWidth(-5);
        r1.setLength(-3);

        int area = r1.getArea();
        int perimeter = r1.getPerimeter();

        r1.print(area, perimeter);
    }
}

内容的提问来源于stack exchange，提问作者msalaz03