java - 已声明的变量无法解析

Question

双宽度无法与 int 墙一起解析，即使在我开始表面积计算之前，它已编译。

import java.util.Scanner;
public class Assignment_3_4 {
    public static void main(String[] args) {
    Scanner in = new Scanner(System.in);

    //Customer Name

    System.out.println("Enter your First Name");
    String Firstn = in.next();
    System.out.println("Enter your Last Name");
    String Lastn = in.next();
    System.out.println("Valued Customer Name: " + Firstn + " " + Lastn);

    //Wall Measurements

    System.out.println("Enter the Width");
    if(in.hasNextDouble()){
        double width = in.nextDouble();
        System.out.println("Width/Height: " + width);
    } else {
        System.out.println("Please enter only numbers");
    }
    System.out.println("Enter number of walls");
    if(in.hasNextInt()){
        int walls = in.nextInt();
        System.out.println("Number of Walls: " + walls);
    } else {
        System.out.println("Please enter only integers");
    }
    //Calculate Surface Area - Width Height and Length are all the same measurement
    double SA = ((width * width) * walls);
    System.out.println("Area to be Painted: " + SA + " square meters");

Answer 1

Java 有所谓的 block scope

在 block {} 内声明的任何变量都无法在 block 外部访问。您可以使用作用域之外的变量，但反之则不行。您需要做的是在范围之外声明变量。您可能还想向用户抛出异常。

double width;
if(in.hasNextDouble()){
    width = in.nextDouble();
    System.out.println("Width/Height: " + width);
} else {
    throw new IllegalArgumentException("Please enter only numbers");
}