为什么代码不会进入提示用户退出或继续的下一行

Question

我有一个程序可以计算用户选择的形状的面积。我提供了 4 种形状，在它们离开后，我想提示他们继续或退出。但是，在程序要求形状和所有内容之后，它会停止并且在第一个 switch 语句之后不会进入任何代码。

我尝试使代码成为 switch 语句的一部分，但由于错误，它无法运行。我也试图做另一个开关，如你所见，但什么都没有。

import java.util.Scanner;
import java.lang.Math;
public class area
{
public static void main(String[] args)
{
Scanner scan = new Scanner(System.in);
String square;
String circle;
String rectangle;
String triangle;
System.out.println("Please choose one of the shapes you want the area of.");
System.out.println("Square, Circle, Rectangle, Triangle.");
String shape = scan.nextLine();
switch (shape)
{
case "Square":
System.out.println("Please enter the length of one side of the square.");
double squareLength = scan.nextDouble();
double squareArea = (squareLength * squareLength);
System.out.println("The area of your square is "+ squareArea + ".");
break;
case "Circle":
System.out.println("Please enter the radius of the circle.");
double circleRadius = scan.nextDouble();
double circleArea = (circleRadius * circleRadius)*Math.PI;
System.out.println("The area of your circle is " + circleArea + ".");
break;
case "Rectangle":
System.out.println("Please enter the width of the rectangle.");
double rectangleWidth = scan.nextDouble();
System.out.println("Please enter the length of the rectangle.");
double rectangleLength = scan.nextDouble();
double rectangleArea = (rectangleWidth * rectangleLength);
System.out.println("The area of your rectangle is " + rectangleArea + ".");
break;
case "Triangle":
System.out.println("Please enter the height of the trangle.");
double triangleHeight = scan.nextDouble();
System.out.println("Please enter the base of the trangle.");
double triangleBase = scan.nextDouble();
double triangleArea = (triangleHeight * triangleBase) / 2;
System.out.println("The area of your triangle is " + triangleArea + ".");
break;
default:
System.out.println("Please choose an option.");
}
System.out.println("Press c to continue and or q to quit.");
String option = scan.nextLine();
switch (option)
{
case "c":
break;
case "q":
System.out.println("Have a good day!");
break;
}
}
}

程序只运行到第一个 switch 语句，之后的所有内容都没有发生。

Answer 1

首先，您需要将switch case放入while loop中，这样，当option等于"c"时，程序将执行。 其次，上面的人放了一个参考Possible duplicate of Scanner is skipping nextLine() after using next() or nextFoo()?。因此，当您使用nextDouble读取值，然后尝试使用nextLine读取时，scan 将跳过下一个nextLine。在此之后，您需要放置另一个nextLine供程序识别它。

public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
String option = "c";
while(option.equals("c")){    
System.out.println("Please choose one of the shapes you want the area of.");
System.out.println("Square, Circle, Rectangle, Triangle.");
String shape = scan.nextLine();
switch (shape) {
case "Square":
System.out.println("Please enter the length of one side of the square.");
double squareLength = scan.nextDouble();
double squareArea = (squareLength * squareLength);
System.out.println("The area of your square is " + squareArea
+ ".");
break;
case "Circle":
System.out.println("Please enter the radius of the circle.");
double circleRadius = scan.nextDouble();
double circleArea = (circleRadius * circleRadius) * Math.PI;
System.out.println("The area of your circle is " + circleArea
+ ".");
break;
case "Rectangle":
System.out.println("Please enter the width of the rectangle.");
double rectangleWidth = scan.nextDouble();
System.out.println("Please enter the length of the rectangle.");
double rectangleLength = scan.nextDouble();
double rectangleArea = (rectangleWidth * rectangleLength);
System.out.println("The area of your rectangle is "
+ rectangleArea + ".");
break;
case "Triangle":
System.out.println("Please enter the height of the trangle.");
double triangleHeight = scan.nextDouble();
System.out.println("Please enter the base of the trangle.");
double triangleBase = scan.nextDouble();
double triangleArea = (triangleHeight * triangleBase) / 2;
System.out.println("The area of your triangle is " + triangleArea
+ ".");
break;
default:
System.out.println("Please choose an option.");
break;
}
scan.nextLine();
System.out.println("Press c to continue and or q to quit.");
option = scan.nextLine();
}
}