有没有办法用java递归检查字符串是否包含至少一个大写字母？

Question

I get IndexOutOfBoundsException exceptions probably because of the charAt method but I'm stuck. I know I have to use isUpperCase but I'm not sure exactly where.

public static boolean hasCapitals(String s) {
    if(Character.isUpperCase(s.charAt(0))) {
        return true;
    } else {
        return hasCapitals(s.substring(1));
    }
}

public static void main( String[] args ){
    System.out.println( hasCapitals( "New Hampshire" ) ); // returns true
    System.out.println( hasCapitals( "word" ) ); // returns false
    System.out.println( hasCapitals( "I" ) ); // returns true
    System.out.println( hasCapitals( "" ) ); // returns false
}

Answer 1

You must have a breaking condition in recursion to finally come out. That condition is missing in your code and you are getting the exception when length of your string is 1.

Try checking String's length before calling isUpperCase.

public static boolean hasCapitals(String s) {
    if(s == null || s.length() == 0) {
        return false;
    }
    if(Character.isUpperCase(s.charAt(0))) {
        return true;
    } else if(s.length() > 1){
        return hasCapitals(s.substring(1));
    } else {
        return false;
    }
}

Answer 2

try like this, does exactly what you need

public static void main(String[] args) {
    System.out.println( hasCapitals( "New Hampshire", 0 ) );
    System.out.println( hasCapitals( "word", 0 ) );
    System.out.println( hasCapitals( "I", 0 ) );
    System.out.println( hasCapitals( "", 0 ) );
    System.out.println( hasCapitals( "hamPshire", 0 ) );
}

private static boolean hasCapitals(String value, int index) {
    if(value.isEmpty()) {
        return false;
    }

    if(Character.isUpperCase(value.charAt(index))) {
        return true;
    } else if(value.length() > (index + 1)) {
        return hasCapitals(value, index + 1);
    } 

    return false;

}