方法参数的问题...Java

Question

@Rogue 这是我设置它的新方法......我目前收到“找不到符号”错误。我仔细检查并声明了我的对象（r​​ectangle4）。 任何想法为什么？再次感谢兄弟...

package rectanglewithprivatedatafields;

class RectangleTestFile
{
public static void main(String[] args)
{
    double lengths = rectangle4.getLengths();
    double widths = rectangle4.getAreas();

//rectangle object 4
RectangleWithPrivateDataFields rectangle4 = new RectangleWithPrivateDataFields();
System.out.println("\nUser Specified Rectangle 4");
System.out.println("Please enter the appropriates sizes for your rectangle: \n");
System.out.println(rectangle4.getWidths());
System.err.println(rectangle4.getLengths());
System.out.println(rectangle4.getPerimeters(rectangle4.getLengths(), rectangle4.getWidths())); 
System.out.println(rectangle4.getAreas(rectangle4.getLengths(),rectangle4.getWidths()));
 }//main
}

Answer 1

你指的是rectangle4.getPerimeters(rectangle4.getLengths(), rectangle4.getWidths())而不是rectangle4.getPerimeters(lengths, widths)？

您的实用程序类没有任何私有成员变量，只有公共访问器方法。

Answer 2

lengths 和 widths 不是您的 main 方法中的变量，因此请制作它们：

int lengths = rectangle4.getLengths();
int widths = rectangle4.getWidths();

由于这些方法读取输入，您应该只调用它们一次。另外据我记得Scanner 消耗System.in 流，所以我只会做一次。继续前进（为了面向对象编程），我会让构造函数接受Scanner 来构建自己，然后让方法返回我需要的值：

//Simple, short class names are easier to work with
public class Rectangle {

    //length and width is data, or "state" of our rectangle, so store it
    private final int length;
    private final int width;

    //Allow creating it without requiring input
    public Rectangle(int width, int length) {
        this.width = width;
        this.length = length;
    }

    //We create ourselves given a Scanner which we can take input from
    public Rectangle(Scanner input) {
        System.out.print("Length: ");
        this.length = input.nextDouble();
        System.out.print("Width: ");
        this.width = input.nextDouble();
    }

    //Calculate based around known information
    public double getArea() {
        return this.length * this.width;
    }

    //Calculate based around known information
    public double getPerimeter() {
        return 2 * (this.length + this.width);
    }

    //getter
    public int getLength() {
        return this.length;
    }

    //getter
    public int getWidth() {
        return this.width;
    }

}

因此像这样调用它：

public static final void main(String... args) {
    Scanner input = new Scanner(System.in); //make once
    Rectangle rect = new Rectangle(input); //let our rectangle do all the work
    //Simple!
    System.out.println("Your rectangle has a width of " + rect.getWidth()
            + ", a length of " + rect.getLength()
            + ", the perimeter " + rect.getPerimeter()
            + ", and an area of " + rect.getArea());
}

这里的关键思想是数据和角色的分离——Rectangle 将管理信息和自身创建的所有方面；无论您是手动提供length 和width，还是为它提供获取该信息的方法（我们的Scanner）。 Rectangle 将存储它需要的信息并返回我们想要的任何其他信息（我们的方法）。这使得类的计算和使用变得非常简单（您将输入传递给它，现在您的工作是从外部角度完成的）。