java - 开关盒内的字符串返回null

所有变量均已正确初始化，并且仅在此方法内定义，将day调用为整数，然后设置为可读取的字符串，然后拆分为字符以创建单词格式。
另外，使用dayL（整数）的数学有时会返回StringIndexOutOfBounds异常，我理解这是由于使用.length（）创建的不等式导致的错误所致。
感谢您的任何帮助。

    public static void bday()
{
    s_day = Integer.toString(day);
    dayL = s_day.length();

    switch (dayL)
    {
    case 1:
        if(s_day.charAt(0) == 1)
        {
            word_day = "first";
        }
        else if(s_day.charAt(0) == 2)
        {
            word_day = "second";
        }
        else if(s_day.charAt(0) == 3)
        {
            word_day = "third";
        }
        else if(s_day.charAt(0) == 4)
        {
            word_day = "fourth";
        }
        else if(s_day.charAt(0) == 5)
        {
            word_day = "fifth";
        }
        else if(s_day.charAt(0) == 6)
        {
            word_day = "sixth";
        }
        else if(s_day.charAt(0) == 7)
        {
            word_day = "seventh";
        }
        else if(s_day.charAt(0) == 8)
        {
            word_day = "eighth";
        }
        else if(s_day.charAt(0) == 9)
        {
            word_day = "ninth";
        }
        break;

    case 2:
        //teens

        if(s_day.charAt(0) == 1 && s_day.charAt(1) == 0)
        {
            word_day = "tenth";
        }
        else if(s_day.charAt(0) == 1 && s_day.charAt(1) == 1)
        {
            word_day = "eleventh";
        }
        else if(s_day.charAt(0) == 1 && s_day.charAt(1) == 2)
        {
            word_day = "twelfth";
        }
        else if(s_day.charAt(0) == 1 && s_day.charAt(1) == 3)
        {
            word_day = "thirteenth";
        }
        else if(s_day.charAt(0) == 1 && s_day.charAt(1) == 4)
        {
            word_day = "fourteenth";
        }
        else if(s_day.charAt(0) == 1 && s_day.charAt(1) == 5)
        {
            word_day = "fifteenth";
        }
        else if(s_day.charAt(0) == 1 && s_day.charAt(1) == 6)
        {
            word_day = "sixteenth";
        }
        else if(s_day.charAt(0) == 1 && s_day.charAt(1) == 7)
        {
            word_day = "seventeenth";
        }
        else if(s_day.charAt(0) == 1 && s_day.charAt(1) == 8)
        {
            word_day = "eighteenth";
        }
        else if(s_day.charAt(0) == 1 && s_day.charAt(1) == 9)
        {
            word_day = "ninteenth";
        }

        //twenties

        if(s_day.charAt(0) == 2 && s_day.charAt(1) == 0)
        {
            word_day = "twentieth";
        }
        else if(s_day.charAt(0) == 2 && s_day.charAt(1) == 1)
        {
            word_day = "twenty-first";
        }
        else if(s_day.charAt(0) == 2 && s_day.charAt(1) == 2)
        {
            word_day = "twenty-second";
        }
        else if(s_day.charAt(0) == 2 && s_day.charAt(1) == 3)
        {
            word_day = "twenty-third";
        }
        else if(s_day.charAt(0) == 2 && s_day.charAt(1) == 4)
        {
            word_day = "twenty-fourth";
        }
        else if(s_day.charAt(0) == 2 && s_day.charAt(1) == 5)
        {
            word_day = "twenty-fifth";
        }
        else if(s_day.charAt(0) == 2 && s_day.charAt(1) == 6)
        {
            word_day = "twenty-sixth";
        }
        else if(s_day.charAt(0) == 2 && s_day.charAt(1) == 7)
        {
            word_day = "twenty-seventh";
        }
        else if(s_day.charAt(0) == 2 && s_day.charAt(1) == 8)
        {
            word_day = "twenty-eighth";
        }
        else if(s_day.charAt(0) == 2 && s_day.charAt(1) == 9)
        {
            word_day = "twenty-ninth";
        }

        //thirties

        if(s_day.charAt(0) == 3 && s_day.charAt(1) == 0)
        {
            word_day = "thirtieth";
        }
        else if(s_day.charAt(0) == 3 && s_day.charAt(1) == 1)
        {
            word_day = "thirty-first";
        }
        break;
    }
    System.out.println("Your birthday is: " + s_month + " "+ word_day);
}

最佳答案

每次比较字符时，您做错了。

s_day.charAt(0) == 1

应该

s_day.charAt(0) == '1'

但这甚至比需要的还要复杂。您在变量int中将日期作为day，对吗？那么，为什么不基于此做出一个if语句呢？

if (day == 1) {
  word_day = "first";
}else if (day == 2)
//and so on