java Simple for loop，初学者

Question

当你看到我的问题时，你就会知道我是Java新手。 我想：

• 用转换菜单提示用户
• 例如，如果他们选择5，请他们输入一个要转换为千克的输入
• 继续给他们菜单，直到他们输入7退出

我的代码的问题是 -无论最初点击哪个数字，上面的第2步都不会出现。它仅在输入第二个数字后出现 -当7英寸进入时，它实际上并没有退出

我也是这个网站的新手，如果我问的问题不恰当，我深表歉意

这是密码

class Test
{
    public static void main(String[] args)
    {
        int number;
        int index;
        int input;
        Double conversion;

        index = 1;

        System.out.println("Enter 1 for Fahrenheit to Celius ");
        System.out.println("Enter 2 for Celius to Fahrenheit ");
        System.out.println("Enter 3 for Inches to Centimetres ");
        System.out.println("Enter 4 for Centimetres to Inches ");
        System.out.println("Enter 5 for Pounds to Kg ");
        System.out.println("Enter 6 for Kg to Pounds ");
        System.out.println("Enter 7 to quit ");
        number = EasyIn.getInt();

        for (index=1; index <=6; index++)

        {
            System.out.println("Enter 1 for Fahrenheit to Celsius ");
            System.out.println("Enter 2 for Celsius to Fahrenheit ");
            System.out.println("Enter 3 for Inches to Centimetres ");
            System.out.println("Enter 4 for Centimetres to Inches ");
            System.out.println("Enter 5 for Pounds to Kg ");
            System.out.println("Enter 6 for Kg to Pounds ");
            System.out.println("Enter 7 to quit ");
            number = EasyIn.getInt();

        if (number == 1)
            {
                System.out.print("Input an amount to convert to Celsius ");
                input = EasyIn.getInt();
                conversion = (5.0/9.0) * (input - 32);
                System.out.println("Your input to Celsius is " + conversion);
                System.out.println("Press 7 to quit");
            }

        if (number == 2)
            {
                System.out.print("Input an amount to convert to Fahrenheit ");
                input = EasyIn.getInt();
                conversion = input * 2.8;
                System.out.println("Your input to Fahrenheit is " + conversion);
                System.out.println("Press 7 to quit");
            }

        if (number == 3)
            {
                System.out.print("Input an amount to convert to Centimetres ");
                input = EasyIn.getInt();
                conversion = input * 2.54;
                System.out.println("Your input to Centimtres is " + conversion);
                System.out.println("Press 7 to quit");
            }

        if (number == 4)
            {
                System.out.print("Input an amount to convert to Inches ");
                input = EasyIn.getInt();
                conversion = input * 0.393701;
                System.out.println("Your input to Inches is " + conversion);
                System.out.println("Press 7 to quit");
            }

        if (number == 5)
            {
                System.out.print("Input an amount to convert to Kg ");
                input = EasyIn.getInt();
                conversion = input * 0.453592;
                System.out.println("Your input to Kgs is " + conversion);
                System.out.println("Press 7 to quit");
            }

        if (number == 6)
            {
                System.out.print("Input an amount to convert to Pounds ");
                input = EasyIn.getInt();
                conversion = input * 2.20462;
                System.out.println("Your input to pounds is " + conversion);
                System.out.println("Press 7 to quit");
            }
        }
    }
}

Answer 1

如果在四个循环中使用索引，可以这样修改循环：

while (number != 7) {
    // ...
}

在第一次迭代中，您将显示两次菜单。循环前一个，循环内另一个。您可以删除循环前显示菜单的代码，并初始化循环值，或使用do while bucle

do {
    // Show menu code
    // Read user action
    // Selected action code
} while (number != 7)

Answer 2

System.out.print("Input an amount to convert to Celsius ");

在System.out流被显式刷新或打印新行之前，该输出不会到达显示器。在这两种情况发生之前，您会继续期待用户输入，因此不会看到提示

这是因为一般来说，当大量数据通过输出流发送时，输出流被缓冲以优化性能PrintStream有自动刷新行为，这使得这个问题在大多数情况下不可见。它的工作原理是在行的每一端刷新标记，而不是用print发送