I cannot understand the code below. but i keep trying

Question

// Is the passed string a number?
public static boolean isNumber(String s) {
if (s.length() == 0) {
return false;
}

char[] chars = s.toCharArray();
for (int i = 0; i < chars.length; i++) {
char c = chars[i];
if (i != 0 && c == '-') { // the string contains a hyphen
return false;
}
if (!Character.isDigit(c) && c != '-') { // not a number and doesn't start with a hyphen
return false;
}
if (i == 0 && c == '-' && chars.length == 1) { // not a hyphen
return false;
}
}
return true;
}
Or
Plis give me a string or number that satisfy each of the last 3 if statements.
Besides i believe the second last if statement will never be satisfied because c cannot have two values at the same time.
Am i correct please help.

Answer 1

stephen haokip

When c = '-' than .isDigit(c) would return false but it could be a minus so you need to make sure that you only return false when c is a letter or another special character(+, &, ? ...)

Answer 2

Hello stephen haokip

if s.length() == 0 means if the string is empy. Should be clear that you return false here.

Now you create an char array.

if(i != 0 && c == '-')
Negative numbers like -4 contains a minus at i = 0.
If "-" somewhere else return false
e.g. s = "1-2", '-' is at i = 1

if(!Character.isDigit(c) && c!='-')
c is not a digit and not a minus -> something else (e.g. a letter) so return false
e.g. s = "12&45", s = "hello"
But if the first char is '-' don't return false because it could be a negative number.

if(i==0 && c == '-' && chars.length() == 1)

The first char is a minus but your char array contains only one char -> return false.
e.g. s = "-"
A negative number would have at least a length of 2

So your code works for positive numbers and negative numbers.

Answer 3

Denise thank you

Answer 4

Denise but i still have doubt

Answer 5

stephen haokip

Just ask.

Answer 6

Denise ...IsDigit part... HoW can c have two values at the same time