sc.hasNextLine() 无限循环

Question

我正在尝试使用输入，但我遇到了麻烦...如果我使用下面的代码，它还没有结束...所以我处于无限循环中。它写了类似的东西，即使我的输入有文件结尾：

...
A number has not been parsed from line n
A number has not been parsed from line n+1
A number has not been parsed from line n+2
... (infinite)

但我想用这个代替：

...
End of input detected!

输入看起来像这样：

double[] numbers = new double[10];
int counter_number = 0;
while (sc.hasNextLine()) {
        ...
        line++;
        if(sc.hasNextDouble()) {
            numbers[counter_number] = sc.nextDouble();
            counter_number++;
        }
        else{
            System.out.println("A number has not been parsed from line "+ line);
            continue;
        }
        if (sc.hasNextLine() == false) {
            System.err.println("End of input detected!");
        }
        if (((counter_number)==10) || ((sc.hasNextLine() == false) 
                ...
            counter_number = 0;
        }
    }

虽然这个循环永远不会结束？我看到他们使用 "while (sc.hasNextLine())" 的教程并完成了。我是 java.

的初学者

Answer 1

您唯一执行 reader 的执行是 sc.nextDouble()，但这仅在 sc.hasNextDouble() returns 为真时才会发生。这意味着如果你的代码遇到非双重输入，它将永远卡住

一般说明 - sc.hasNextLine() == false 应替换为 !sc.hasNextLine()

Answer 2

static Scanner sc = new Scanner(System.in);
public static void main(String[] args) {
    double[] numbers = new double[10];
    int counter_number = 0;
    int line = 0;

    while (sc.hasNextLine()){

        line++;

        String thisLine = sc.nextLine();
        // this is what i wrote.

        if(thisLine.trim().isEmpty()) {
            // if the line is empty, will exit the loop.

            System.out.println("lines: "+line); // lines
            System.out.println("End of input detected!"); // end.
            break;
        }

        try {
            // if the input is a double
            numbers[counter_number] = Double.parseDouble(thisLine);
            counter_number++;

        } catch (NumberFormatException e) {
            // if not
            System.out.println("A number has not been parsed from line "+ line);
            continue;
        }

        // idk
        if (counter_number == numbers.length) {
            counter_number = 0;
        }
    };

}

修复。我不会关闭扫描器而且...你试试这个。当我键入一个空行时，此代码结束。

sc.hasNextLine() 无限循环

Infinite loop with sc.hasNextLine()

java

loops

input

infinite-loop

output