读取char输入中的多个字符并转换为double

Question

    public static void main(String[] args) 
{
    char ch;

    ch = JOptionPane.showInputDialog("").charAt(0);

    if (Character.isLetter(ch))
    {
        System.out.println(Character.toUpperCase(ch));
    }

    if (Character.isDigit(ch))
    {
        Math.sqrt(ch);
        System.out.println(ch);
    }

    if (Character.isWhitespace(ch))
    {
        int code = ch;
        System.out.println (code);
    }
}

If I input more than one character, it only recognises the first character. How do I make the program see multiple characters that a user inputs as a char?

Answer 1

You are taking only the first character with this:-

 ch = JOptionPane.showInputDialog("").charAt(0);

The charAt(0) gives you the character with the index of 0 , which is always the first character.

If you want to treat your input as a Whole and not only the First character, try using a String as follows

String s = JOptionPane.showInputDialog("");

Also note that your Charater.isLetter(ch) won't work now, as you can't do that with a String . However, you can convert the whole String to UpperCase if you want. Also, you can't easily look whether String is a valid Double or not. It requires exception handling and may be confusing. I am including it anyway, so if you are confused,feel free to ask.

The Final Program looks like this:-

String s;
s = JOptionPane.showInputDialog("");
try{
    double d = Double.parseDouble(s);
}catch(Exception e){
    //Not a Double as it comes inside catch
    //Therefore String must be empty or contain Characters

    //Checking for Empty

    if(s.trim().length()<1){
    //String is empty 
    //Do what you want
    System.out.println("String is whitespace");
    }else {
       //String must contain Characters.
       System.out.println(s.toUpperCase());
    }
}

Please ask, if you are stuck at anything.