java - 为什么程序在读取下一行之前就运行了？

Question

这个问题已经有答案了:

Scanner is skipping nextLine() after using next() or nextFoo()? (25 个回答)

已关闭 6 年前。

public class Solution {

    public static void main(String[] args) {
        int i = 4;
        double d = 4.0;
        String s = "HackerRank ";

        Scanner scan = new Scanner(System.in);
        /* Declare second integer, double, and String variables. */
        /* Read and save an integer, double, and String to your variables.*/
        int sec = scan.nextInt(); 
        double db = scan.nextDouble(); 
        String newWord = scan.nextLine(); 

        /* Print the sum of both integer variables on a new line. */
        System.out.println(i + sec);
        /* Print the sum of the double variables on a new line. */
        System.out.println(d + db);
        /* Concatenate and print the String variables on a new line; 
            the 's' variable above should be printed first. */
        System.out.println(s + newWord);
        scan.close();
    }
}

如果String newWord = scan.nextLine();位于 int sec = scan.nextInt(); 之前不过它工作得很好。

Answer 1

只需将 String newWord = scan.nextLine(); 替换为 String newWord = scan.next();

这里:

    double db = scan.nextDouble(); 
    String newWord = scan.nextLine(); 

scan.nextDouble() 不会读取所有行，仅读取 double 行。
因此，scan.nextLine()将当前行的其余部分分配给newWord变量，即一个空的String:"".

If String newWord = scan.nextLine(); is placed before int sec = scan.nextInt(); it works fine though.

确实是因为 "" 是字符串的有效值。因此，当您执行此操作时，newWord 具有 "" 值。

<小时/>

编辑评论

尽量避免将 nextInt()、nextDouble() 等与 nextLine() 方法混合使用。
您可以执行 nextLine() 来读取空字符串，然后再次执行另一个 nextLine() 来读取用户的输入。

或者，即使对于数字类型，您也只能使用 nextLine() 并从 String 输入创建数值。这是您的代码的示例:

public static void main(String[] args) {
    int i = 4;
    double d = 4.0;
    String s = "HackerRank ";

    Scanner scan = new Scanner(System.in);
    /* Declare second integer, double, and String variables. */
    /* Read and save an integer, double, and String to your variables.*/
    int sec = Integer.valueOf(scan.nextLine()); 
    double db = Double.valueOf(scan.nextLine()); 
    String newWord = scan.nextLine(); 

    /* Print the sum of both integer variables on a new line. */
    System.out.println(i + sec);
    /* Print the sum of the double variables on a new line. */
    System.out.println(d + db);
    /* Concatenate and print the String variables on a new line; 
        the 's' variable above should be printed first. */
    System.out.println(s + newWord);
    scan.close();
}