我需要做的就是再次循环，以便用户可以继续使用该程序。如果有任何我可以阅读的参考资料，请告诉我，以帮助我更多地了解这个问题。提前谢谢。
import java.util.Scanner;
public class Module3Assignment1 {
// public variables
public static String letterChosen;
public static int loop = 0;
public static double radius, area;
public static Scanner scanner = new Scanner(System.in);
public static void main(String[] args) {
// tells user what the program is about
System.out.println("Welcome to the Round Object Calculator");
System.out.println("This program will calculate the area of a circle of the colume of a sphere.");
System.out.println("The calculations will be based on the user input radius.");
System.out.println("");
// loops while the user wants to calculate information
while (loop == 0){
Input();
System.out.print(Answer());
System.out.println("Do you want to calculate another round object (Y/N)? ");
String input = scanner.next().toUpperCase();
if (input == "N"){
loop = 1;
}
}
// ending message/goodbye
Goodbye();
scanner.close();
}
private static void Input(){
// prompts user for input
System.out.print("Enter C for circle or S for sphere: ");
letterChosen = scanner.nextLine().toUpperCase();
System.out.print("Thank you. What is the radius of the circle (in inches): ");
radius = scanner.nextDouble();
}
private static double AreaCircle(){
// calculates the area of a circle
area = Math.PI * Math.pow(radius, 2);
return area;
}
private static double AreaSphere(){
// calculates the area of a sphere
area = (4/3) * (Math.PI * Math.pow(radius, 3));
return area;
}
private static String Answer(){
//local variables
String answer;
if(letterChosen == "C"){
// builds a string with the circle answer and sends it back
answer = String.format("%s %f %s %.3f %s %n", "The volume of a circle with a radius of", radius, "inches is:", AreaCircle(), "inches");
return answer;
}else{
// builds a string with the sphere answer and sends it back
answer = String.format("%s %f %s %.3f %s %n", "The volume of a sphere with a radius of", radius, "inches is:", AreaSphere(), "cubic inches");
return answer;
}
}
private static String Goodbye(){
// local variables
String goodbye;
// says and returns the goodbye message
goodbye = String.format("%s", "Thank you for using the Round Object Calculator. Goodbye");
return goodbye;
}
}
以下是控制台输出和执行后我得到的错误
Welcome to the Round Object Calculator
This program will calculate the area of a circle of the colume of a sphere.
The calculations will be based on the user input radius.
Enter C for circle or S for sphere: C
Thank you. What is the radius of the circle (in inches): 12
The volume of a sphere with a radius of 12.000000 inches is: 5428.672 cubic inches
Do you want to calculate another round object (Y/N)?
Y
Enter C for circle or S for sphere: Thank you. What is the radius of the circle (in inches): C
Exception in thread "main" java.util.InputMismatchException
at java.util.Scanner.throwFor(Scanner.java:840)
at java.util.Scanner.next(Scanner.java:1461)
at java.util.Scanner.nextDouble(Scanner.java:2387)
at Module3Assignment1.Input(Module3Assignment1.java:48)
at Module3Assignment1.main(Module3Assignment1.java:24)
答案 0 :(得分：0)
概念一
在比较Java中的字符串
时始终使用.equals Method
所以
if(letterChosen == "C")
应该是if(letterChosen.equals("C"))，而其他人
概念二。
这可能是您的代码发生的原因之一。 您已经从扫描仪类的键盘对象获取了一个UserInput，这就是为什么它会给出else响应。当您从该对象输入非String输入时，尤其会发生这种情况
这是因为Scanner＃nextDouble方法没有读取输入的最后一个换行符，因此在下次调用Scanner＃nextLine时会消耗该换行符。
WorkAround Fire a blank Scanner#nextLine call after Scanner#nextDouble to consume newline.
Or Use Two Scanner Object.
演示使用相同的扫描程序对象为nextLine（）和nextInt（）发生了什么
公共课测试{
public static void main(String[] args) {
Scanner keyboard= new Scanner(System.in);
int n=keyboard.nextInt();
String userResponse;
while(true) {
userResponse = keyboard.nextLine();
if(userResponse.length() == 1 && userResponse.charAt(0) == 'y') {
System.out.println("Great! Let's get started.");
break;
}
else if(userResponse.length() == 1 && userResponse.charAt(0) == 'n') {
System.out.println("Come back next time " + "" + ".");
System.exit(0);
}
else {
System.out.println("Invalid response.");
}
}
}
}
输出
5
Invalid response.
现在更改代码结构以从该扫描程序对象获取字符串输入，而不是获取代码工作的另一种数据类型。
使用String作为上一个输入
public class Test {
public static void main(String[] args) {
Scanner keyboard= new Scanner(System.in);
String n=keyboard.nextLine();
String userResponse;
while(true) {
userResponse = keyboard.nextLine();
if(userResponse.length() == 1 && userResponse.charAt(0) == 'y') {
System.out.println("Great! Let's get started.");
break;
}
else if(userResponse.length() == 1 && userResponse.charAt(0) == 'n') {
System.out.println("Come back next time " + "" + ".");
System.exit(0);
}
else {
System.out.println("Invalid response.");
}
}
}
}
输出
j
y
Great! Let's get started.
没有任何先前对该对象的响应，您的代码将起作用。
public class Test {
public static void main(String[] args) {
Scanner keyboard= new Scanner(System.in);
String userResponse;
while(true) {
userResponse = keyboard.nextLine();
if(userResponse.length() == 1 && userResponse.charAt(0) == 'y') {
System.out.println("Great! Let's get started.");
break;
}
else if(userResponse.length() == 1 && userResponse.charAt(0) == 'n') {
System.out.println("Come back next time " + "" + ".");
System.exit(0);
}
else {
System.out.println("Invalid response.");
}
}
}
}
并给我所需的输出
y
Great! Let's get started.
我通常一直在创建两个OBJECT of Scanner Class 1来获取String Input而其他来获取其他数据类型输入 （太坦率了，即使我一直无法弄清楚为什么我需要在java中创建两个用于接收String和其他数据类型的Object而没有任何错误。如果有人知道请告诉我）
答案 1 :(得分：0)
import java.util.Scanner;
public class Module3Assignment1 {
// public static variables are discouraged...
private static char letterChosen; //char takes less memory
private static char useAgain = 'Y'; //just use the answer to loop...
private static double radius, area;
private static String answer;
private static Scanner scanner = new Scanner(System.in);
//you might want to clear the screen after the user gave an answer to another round object
private static void clearScreen(){
for(int i =0;i<50;i++){System.out.print("\n");}
}
public void input(){
// prompts user for input
System.out.print("Enter C for circle or S for sphere: ");
letterChosen = scanner.next().charAt(0);
System.out.print("Thank you. What is the radius of the circle (in inches): ");
radius = scanner.nextDouble();
this.answer= answer(letterChosen);
}
public double areaCircle(double radius){
// calculates the area of a circle
area = Math.PI * Math.pow(radius, 2);
return area;
}
public double areaSphere(double radius){
// calculates the area of a sphere
area = (4/3) * (Math.PI * Math.pow(radius, 3));
return area;
}
public String answer(char letterChosen){
//local variables
String answer = "";
if(letterChosen=='c'||letterChosen=='C'){
answer = String.format("%s %f %s %.3f %s %n", "The volume of a circle with a radius of", radius, "inches is:", areaCircle(radius), "inches");
}else{
answer = String.format("%s %f %s %.3f %s %n", "The volume of a sphere with a radius of", radius, "inches is:", areaSphere(radius), "cubic inches");
}
return answer;
}
private static String goodbye(){
// local variables
String goodbye;
// says and returns the goodbye message
goodbye = String.format("%s", "Thank you for using the Round Object Calculator. Goodbye");
return goodbye;
}
public static void main(String[] args) {
// tells user what the program is about
System.out.println("Welcome to the Round Object Calculator");
System.out.println("This program will calculate the area of a circle of the colume of a sphere.");
System.out.println("The calculations will be based on the user input radius.");
System.out.println("");
Module3Assignment1 ass1 = new Module3Assignment1();
// loops while the user wants to calculate a round object
while (useAgain == 'Y'||useAgain=='y'){
ass1.input();
System.out.print(answer);
System.out.println("Do you want to calculate another round object (Y/N)? ");
useAgain = scanner.next().charAt(0);
System.out.println(useAgain);
clearScreen();
}
// ending message/goodbye
System.out.println(goodbye());
scanner.close();
}
}
我改变了一些事情：
我在areaSphere和areaCircle方法中添加了参数radius。这使得这些方法可以重用。
我将所有公共静态变量更改为private static。使用公共静态变量是高度重新。您可以阅读this以找出原因。
为了防止公共静态变量，我创建了一个Module3Assignment1的实例，而不是让所有东西都是静态的。
更改了方法名称的大小写。请遵循camel-casing，这意味着该方法的第一个字母是小写的，其他单词将以大写形式显示第一个字母（例如input（），areaSphere（））
关于比较字符串的评论：
== 比较参考对象， NOT VALUES
如果要比较两个字符串的值，请使用 .equals（）或 .equalsIgnoreCase（）。这是一个示例语法：
if(string1.equals(string2)){
//do something
}