java - 在比较字符串时，在 Java 中将 if 与 Scanner 结合使用无法正常工作

Question

import java.util.*;

class Sept1Little {
    public static void main (String args []) {

        Scanner s = new Scanner(System.in);

        System.out.println("Hey! I'm not gonna program today o.o but I'm gonna do a little program :3");
        System.out.println("Let's play with some math!");
        System.out.println("Enter two numbers and magic will happen");
        System.out.print("Enter the first number: ");
        float a = s.nextInt();
        System.out.print("Enter the second number: ");
        float b = s.nextFloat();
        float c = (float) Math.pow( a, b);
        System.out.printf("The number is :%f\n" , c);
        System.out.println("We love Bernie Sanders!");
        System.out.println("Come on, let's push him over the line!");
        int poll1 = 30;
        System.out.println("Current poll amount: " + poll1);
        System.out.println("Let's add 7% and an extra 1%!");
        int poll2 = poll1 + 7;
        int poll3 = ++poll2;
        System.out.println("Bernie Sanders would get :" + poll3 + ". Bernie would get a better percentage than Hillo Clinto-Money");
        System.out.println("Write in the best US President Nominee: ");
        String president = Keyboard.readString();
        if (president.equals("Bernie Sanders")){
            System.out.println("You chose Bernie Sanders.");

        }
        else if (president.equals("Donald Trump")) {
            System.out.println("You chose Donald Trump");

        }
        else if (president.equals("Hillary Clinton")) {
            System.out.println("You chose Hillary Clinton ");

        }
        else {
            System.out.println("Choose someone we know...");

        }
        System.out.println("Let's calculate how much money you owe the govt by... SQUARE ROOTING IT!");
        System.out.print("Enter the amount of money you owe the govt: ");
        float debt1 = Keyboard.readFloat();
        System.out.printf("The amount is now :%f\n" , Math.sqrt(debt1));
        System.out.println("Welcome to the Euro to Dollar Convertor!");
        System.out.print("Enter the amount in US Dollars you wish to convert to Euro: ");
        float euro1 = Keyboard.readFloat();
        final float rate = (float) 1.13;
        System.out.printf("The amount in Euro is %f\n" , euro1 / rate);
    }
}

如您所见，我在请求被提名人时使用了 Keyboard.readString();。当我使用 s.readLine(); 时，它不起作用，它会跳到 else 子句，然后崩溃，因为它需要 的总统输入>float 之后的值。抱歉，这有点政治色彩，但我懒得摆弄它。当我将 "Bernie Sanders" 设为 "BernieSanders" 时，我没有收到错误消息，有人知道为什么吗？

Answer 1

我猜这是因为 s.nextFloat(); 和 s.nextInt(); 只读取 float 和 int，而不是整行，所以 Scanner 的光标在 float 或 int 之后，而不是在下一行。这里有一个例子:

如果您的输入是:

5 Bench
Prove

你的代码中有:

a= s.nextInt(); //5
b= s.nextLine(); //" Bench"

为什么它没有捕捉到 Prove 值？因为在使用 s.nextInt() 之后，Scanner 的光标在 5 之后，而不是在下一行(我们在其中的行)有证明)。为避免它，您必须阅读该行的其余部分(对您无用，因为您不想要它)但没有获得此值。像这样:

a= s.nextInt(); //5
s.nextLine(); //We go to the next line
b= s.nextLine(); //"Prove"

附注:每次使用 s.nextInt(); 或 时都必须使用 s.nextLine(); >s.nextFloat(); 作为我上面的例子。

希望对您有所帮助!