java - 预期 & .class 预期 java

Question

我对java有点陌生，所以如果我犯了一个简单的错误，请原谅我，但我不确定我哪里出错了，我收到的错误是“预期的.class，预期的标识符，而不是声明， ';'预期的。”我尝试了不同的方法，并从这些方法中收到了不同的错误，但我认为这些错误是最容易诊断的。预先感谢您的任何回复。 代码:

//main class 
Operation a = new Operation(); 
double area = a.square(double area, double length); // line that receives errors

// Operation class
import java.util.Scanner;
public class Operation
{
    double pi = 3.14;
    double gravity = 9.8;
    double length;
    double width;
    double area;
    Scanner keyboard = new Scanner(System.in);
    public double square(double area, double length)
    {
        System.out.println("Enter length of each side of a square:");
        length = keyboard.nextDouble();
        area = length * length;
        System.out.println(area);
        return area;
    }
}

Answer 1

您正在从命令行读取输入，因此您的 square(...) 方法中不需要任何参数。将其声明为:

public double square()
{
    double area, length;
    System.out.println("Enter length of each side of a square:");
    length = keyboard.nextDouble();
    area = length * length;
    System.out.println(area);
    return area;
}

并在主方法中调用它，如下所示:

double area = a.square();