为什么rec.area 和rec.perimeter 总是0？

Question

我不明白为什么rec.area 和rec.perimeter 只打印0

矩形

class Rectangles {

        int weight;
        int height;
        int area;
        int perimeter;

        int area (int weight, int height) {
            return  weight * height;
        }

        int perimeter (int weight, int height) {
            return  2 * (weight + height);
        }
    }

矩形测试

class RectanglesTest {
    public static void main(String[] args)  {

        Rectangles rec = new Rectangles();

        rec.weight = 10; 
        rec.height = 15; 

        System.out.println(rec.weight);
        System.out.println(rec.height);
        System.out.println(rec.area);
        System.out.println(rec.perimeter);
    }
}

Answer 1

因为area 和perimeter 的值没有改变，在你的方法中你必须将它们设为void 并将计算的值分配给请求的属性

class Rectangles {

        int weight;
        int height;
        int area;
        int perimeter;

        void area () {
            area = weight * height;
        }

        void perimeter () {
            perimeter = 2 * (weight + height);
        }
}

并且在您的main 方法中，您必须先调用这些方法

public static void main(String[] args) {

  Rectangles rec = new Rectangles();

  rec.weight = 10; 
  rec.height = 15; 
  rec.area();
  rec.perimeter();
  System.out.println(rec.weight);
  System.out.println(rec.height);
  System.out.println(rec.area);
  System.out.println(rec.perimeter);
}

Answer 2

您将字段名称与方法名称混淆了 - 最好使它们不同，但无论如何要使用您的代码

public static void main(String[] args) {

  Rectangles rec = new Rectangles();

  rec.weight = 10; 
  rec.height = 15; 

  System.out.println(rec.weight);
  System.out.println(rec.height);
  System.out.println(rec.area ());
  System.out.println(rec.perimeter ());
}

由于你使用的是字段，所以不需要向这些方法传递其他参数，所以将它们更改为

int area () { ....}
int perimeter () { ....}

更好的命名方法是动词，例如计算面积

其实你不用

int area;
int perimeter;

所以你可以删除它们