if语句Java：如何测试输入是double还是int

Question

我有一个做循环。检查x是否在两个值之间。现在，我应该接受一个int值，但是如果用户键入一个double，我就会得到异常。我如何在同一if语句中输入一个检查，以便如果用户键入double，它将打印类似“x必须是介于10和150之间的整数”：

            do {
            x = sc.nextInt();
            if ( x < 10 || x > 150 ) {
                System.out.print("x between 10 and 150: ");
            } else {
                break;
            }

Answer 1

您可以捕获异常并处理它，使用while (true)允许用户重试

这是我的密码：

Scanner sc = new Scanner(System.in);
do {
    System.out.print("\nInsert a number >>> ");
    try {
        int x = sc.nextInt();
        System.out.println("You inserted " + x);
        if (x > 10 && x < 150) {
            System.out.print("x between 10 and 150: ");
        } else {
            break;
        }
    } catch (InputMismatchException e) {
        System.out.println("x must be an int between 10 and 150");
        sc.nextLine(); //This line is really important, without it you'll have an endless loop as the sc.nextInt() would be skipped. For more infos, see this answer http://stackoverflow.com/a/8043307/1094430
    }
} while (true);

Answer 2

public class SomeClass {                                                         
    public static void main(String args[]) {                                     
        double x = 150.999; // 1
        /* int x = (int) 150.999; */ // 2                                          
        if ( x >= 10 && x <= 150 ) { // The comparison will still work                                             
            System.out.print("x between 10 and 150: " + x + "\n");               
        }                                                                        
    }                                                                            
}

1. 将x声明为double，double和int之间的比较仍然有效
2. 或者，强制转换数字，任何十进制值都将被丢弃

Answer 3

您不需要额外的支票。异常就在那里，因此您可以在程序中相应地执行操作。毕竟，输入错误的程度并不重要。只需捕获异常（我想是NumberFormatException吧？）捕获后，打印一条错误消息：

while (true) try {
    // here goes your code that pretends only valid inputs can occur
    break;   // or better yet, put this in a method and return
} catch (NumberFormatException nfex) {  // or whatever is appropriate
    System.err.println("You're supposed to enter integral values.");
    // will repeat due to while above
}