java - 为什么在下面的场景中会抛出不同类型的异常？

Question

我正在尝试使用 Scanner 和 DataInputStream 获取用户的输入。这是我正在使用的代码:

场景 1:

Scanner scanner = new Scanner(System.in);
System.out.print("Enter a number: ");
double d1 = scanner.nextDouble();

场景 2:

DataInputStream din = new DataInputStream(System.in);
System.out.print("Enter a number: ");
double d2 = Double.parseDouble(in.readLine());

当提供一些字符(如 abc)输入时:

在场景 1 中，我收到 InputMismatchException。在场景 2 中，我收到 NumberFormatException。

为什么Scanner抛出不同的异常？有人可以澄清一下吗？

Answer 1

Scanner.nextDouble() 的 JavaDoc 说:

Scans the next token of the input as a double. This method will throw InputMismatchException if the next token cannot be translated into a valid double value. If the translation is successful, the scanner advances past the input that matched.

Returns:

The double scanned from the input

Throws:

InputMismatchException - if the next token does not match the Float regular expression, or is out of range
NoSuchElementException - if the input is exhausted
IllegalStateException - if this scanner is closed

检查您的Scanner.class来源:

public double nextDouble() {
        // Check cached result
        if ((typeCache != null) && (typeCache instanceof Double)) {
            double val = ((Double)typeCache).doubleValue();
            useTypeCache();
            return val;
        }
        setRadix(10);
        clearCaches();
        // Search for next float
        try {
            return Double.parseDouble(processFloatToken(next(floatPattern())));
        } catch (NumberFormatException nfe) {
            position = matcher.start(); // don't skip bad token
            throw new InputMismatchException(nfe.getMessage());
    }
}

尝试解析时，如果 Double.parseDouble() 抛出 NumberFormatException (根据您的场景 2)，则 Scanner.nextDouble() 抛出 InputMismatchException (根据您的场景 1)。