Java 比较值时没有这样的元素异常？

Question

我正在创建一个提示用户输入 3 个数字的应用程序，它会对输入的这些数字进行平均。但是当我到达那里时，它立即抛出一个 noSuchElementException。

    int i1,i2;
    int sum;
    double d1, d2, d3;//declares values input by the user
    double avg; //variable for calculating final result

    System.out.println("Hello out there. \n" //displays information to the user
            + "I will add two numbers for you. \n"
            + "Enter two whole numbers on a line:");

    Scanner keyboardInt = new Scanner(System.in); //Scans for keyboard input
    i1 = keyboardInt.nextInt();
    i2 = keyboardInt.nextInt();
    sum = (i1+i2);
    System.out.println("The sum of those 2 numbers is: \n" + sum + "\n" + 
    "Now enter 3 decimal numbers on a line:");
    keyboardInt.close();

    Scanner keyboardDouble = new Scanner(System.in); //Scans for keyboard input
    d1 = keyboardDouble.nextDouble();//-\ THIS LINE THROWS THE EXCEPTION. ID ASSUME THE OTHER WILL DO THE SAME
    d2 = keyboardDouble.nextDouble();//stores values entered by the user
    d3 = keyboardDouble.nextDouble();//-/
    avg = ((float) (d1+d2+d3)/3.0);//adds the sum of the values entered and calculates the average
    keyboardDouble.close();//closes scanner

    DecimalFormat df = new DecimalFormat("###,###,###.00");//formats the inputed number to 2 decimal places

    System.out.println("The average of those three numbers is:");//displays the average of the numbers
    System.out.println(df.format(avg));                         //entered by the user

这就是问题所在:

Scanner keyboardDouble = new Scanner(System.in); //Scans for keyboard input
d1 = keyboardDouble.nextDouble();//-\ THIS LINE THROWS THE EXCEPTION. ID ASSUME THE OTHER WILL DO THE SAME
d2 = keyboardDouble.nextDouble();//stores values entered by the user
d3 = keyboardDouble.nextDouble();//-/
avg = ((float) (d1+d2+d3)/3.0);//adds the sum of the values entered and calculates the average
keyboardDouble.close();//closes scanner     

Answer 1

删除 keyboardInt.close() 语句。它关闭底层 InputStream，即 System.in。因此，当您创建 keyboardDouble 时，它无法再读取，因为 System.in 已关闭。

因此，要解决这个问题，请使用一个 Scanner，同时用于两个目的:

Scanner keyboard = new Scanner(System.in);
...
i1 = keyboard.nextInt();
i2 = keyboard.nextInt();
...
d1 = keyboard.nextDouble();
d2 = keyboard.nextDouble();
d3 = keyboard.nextDouble();