Comparing a char with multiple characters

Question

for(int j=0 ; j<str.length() ; j++) {
    if(char[j]==(a||e||i||o||u))
        count++;
}

I know the result of (a||e||i||o||u) is a Boolean so can't compare but how can we check for multiple character presence?

Answer 1

This is not doing what you want. Please use a stack switch statement:

for(int j = 0; j < str.length(); j++)
     switch(str.charAt(j)) {
         case 'a':
         case 'e':
         case 'i':
         case 'o':
         case 'u':
             count++;
     }

Or, since I'm a regex enthusiast, here's an approach using regular expressions! :)

Matcher matcher = Pattern.compile("[aeiou]").matcher(str);
while(matcher.find())
    count++;

There was a mistake in this code fixed later on, thanks to user2980077

Answer 2

If you use the classes you can try with regex or simple String

String s = "aeiouaeiou";//string to count
int count = 0;
for (int i = 0; i < s.length(); i++) {

  //One method
  if ("aeiou".indexOf( s.charAt(i) ) >= 0) {
    count++;
  }

  //Another one
  if (Character.toString( s.charAt(i) ).matches("[aeiou]")) {
    count++;
  }

}

Answer 3

If I really need to work with a char[] array and not with a String instance, I always use the Character class and regular expressions. If you don't know what regular expressions are you should learn them because they are very useful when working with strings. Also, you can practice at Regexr.

For your example I'd use this:

char[] data = "programming in Java is fun".toCharArray();
int counter = 0;

for(int i = 0; i<data.length; i++){
    if(Character.toString(data[i]).matches("[aeiou]")){
        counter++;
    }
}

System.out.println(counter); // writes: 8

What the if statement does is basically it makes a new String instance containing the current character just to be able to use the methods from the String class. The method boolean matches(String regex) checks whether your string satisfies the conditions given with the regex argument.

Answer 4

One more for Java 8:

count = str.chars()
           .filter(c -> c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u' )
           .count();

Answer 5

One of the ways to do this in using a List of Character and in java9 could be :

List<Character> vowels = List.of('a','e','i','o','u'); // pverloaded convenience factory method 
for(int j=0 ; j < str.length() ; j++) {
    if(vowels.contains(char[j])) {
        count++;
    }
}

Answer 6

One more for the clever regex department:

count = str.replaceAll("[^aeiou]","").length();