方法不会读取用户输入，并且 do-while 循环不会跳过一行

Question

我正在为一个项目制作一个程序，我不明白为什么即使我的变量被声明为实例变量，该方法也不会读取用户输入，以及如果用户选择"否"作为答案，为什么do-while循环不会跳过某一行。

System.out.println("What Gas Brand Did You Use?");
System.out.println("1 - Diesel");
System.out.println("2 - Unleaded");
gas = console.nextInt();
if (gas == 1){
    diesel();
}
else if (gas == 2){
    unleaded();
}
System.out.println("How Many Liters Did You Cosume?");
liters = console.nextInt();
System.out.println("Do You Want to Buy Some Snack? (1 - Yes or 2 - No)");
choice = console.nextInt();

do{
System.out.println("1 - Water = 20");
System.out.println("2 - Beef Jerky = 50");
add = console.nextInt();
if (add == 1){
    water();
}
else if (add == 2){
    beef();
}
}while(choice == 2); 
fee();

public static void diesel()
{
    total = 30 * liters;    
}
public static void unleaded()
{
    total = 45 * liters;
}
public static void water()
{
    total = total + water;
}
public static void beef()
{
    total = total + beef;
}
public static void fee()
{
    System.out.println("The Total Fee Is: " + total);
}  

Answer 1

在运行diesel()或unleaded()之前，您需要询问升数。否则，该值将默认为0。

您还需要更改do-while循环，以便在他们选择No时它不会运行，并且在他们选择了Yes时它不会进入无限循环。

以下是如何更改它：

System.out.println("What Gas Brand Did You Use?");
System.out.println("1 - Diesel");
System.out.println("2 - Unleaded");
gas = console.nextInt();
System.out.println("How Many Liters Did You Cosume?");
liters = console.nextInt();
if (gas == 1) {
    diesel();
} else if (gas == 2) {
    unleaded();
}
System.out.println("Do You Want to Buy Some Snack? (1 - Yes or 2 - No)");
choice = console.nextInt();
if (choice == 1) {
    System.out.println("1 - Water = 20");
    System.out.println("2 - Beef Jerky = 50");
    add = console.nextInt();
    if (add == 1) {
        water();
    } else if (add == 2) {
        beef();
    }
}
fee();

Answer 2

首先，我想假设控制台对象声明如下：

Scanner console = new Scanner(System.in);

也就是说，你的选择变量不会在do-while循环中重新评估，即使你把提示消息放在do代码块中，如果用户因为你的条件而选择no(2(，while循环也会评估为true：

while(choice == 2);

此外，do-while循环总是在检查while条件之前评估do段中的代码块，因此无论用户在第一个实例中选择了什么，do-wile代码块都将在检查whire条件之前进行评估，因此更好的方法是使用while循环，因此您应该具有以下内容：

System.out.println("Do You Want to Buy Some Snack? (1 - Yes or 2 - No)");
choice = console.nextInt();
while(choice==1){
  System.out.println("1 - Water = 20");
  System.out.println("2 - Beef Jerky = 50");
  add = console.nextInt();
  if (add == 1){
    water();
  }
  else if (add == 2){
    beef();
  }
  System.out.println("Do You Want to Buy Some Snack? (1 - Yes or 2 - No)");
  choice = console.nextInt();
}

因此，最后的代码应该是这样的，注意在评估柴油或无铅汽油之前，你必须先询问升数：

Scanner console = new Scanner(System.in);
System.out.println("What Gas Brand Did You Use?");
System.out.println("1 - Diesel");
System.out.println("2 - Unleaded");
gas = console.nextInt();
System.out.println("How Many Liters Did You Cosume?");
liters = console.nextInt();
if (gas == 1){
    diesel();
}
else if (gas == 2){
    unleaded();
}

System.out.println("Do You Want to Buy Some Snack? (1 - Yes or 2 - No)");
choice = console.nextInt();
while(choice == 1){
  System.out.println("1 - Water = 20");
  System.out.println("2 - Beef Jerky = 50");
  add = console.nextInt();
  if (add == 1){
    water();
  }
  else if (add == 2){
    beef();
  }
  System.out.println("Do You Want to Buy Some Snack? (1 - Yes or 2 - No)");
  choice = console.nextInt();
}
fee();

public static void diesel()
{
    total = 30 * liters;    
}
public static void unleaded()
{
    total = 45 * liters;
}
public static void water()
{
    total = total + water;
}
public static void beef()
{
    total = total + beef;
}
public static void fee()
{
    System.out.println("The Total Fee Is: " + total);
}