Counting a certain character in a String (Java)

Question

String a="(Yeahhhh) I have finally made it to the (top)";

Given above String, there are 4 of '(' and ')' altogether.

My idea of counting that is by utilizing String.charAt method. However, this method is rather slow as I have to perform this counting for each string for at least 10000 times due to the nature of my project.

Anyone has any better idea or suggestion than using .chartAt method?????

Sorry for not explaining clearly earlier on, what I meant for the 10000 times is for the 10000 sentences to be analyzed which is the above String a as only one sentence.

Answer 1

Sounds like homework, so I'll try to keep it at the "nudge in the right direction".

What if you removed all characters NOT the character you are looking for, and look at the length of that string?

There is a String method that will help you with this.

Answer 2

You can use toCharArray() once and iterate over that. It might be faster.

Why do you need to do this 10000 times per String? Why don't you simply remember the result of the first time? This would save a lot more than speeding up a single counting.

Answer 3

StringUtils.countMatches(wholeString, searchedString) (from commons-lang)

searchedString may be one-char - "("

It (as noted in the comments) is calling charAt(..) multiple times. However, what is the complexity? Well, its O(n) - charAt(..) has complexity O(1), so I don't understand why do you find it slow.

Answer 4

You can achieve this by following method.

This method would return a map with key as the character and value as its occurence in input string.

Map countMap = new HashMap();

public void updateCountMap(String inStr, Map<Character, Integer> countMap)
    {
        char[] chars =  inStr.toCharArray();
        for(int i=0;i<chars.length;i++)
        {
            if(!countMap.containsKey(chars[i]))
            {
                 countMap.put(chars[i], 1);
            }
            countMap.put(chars[i] ,countMap.get(chars[i])+1);
        }
        return countMap;        
    }

What we can do is read the file line by line and calling the above method for every line. Each time the map would keep adding the values(number of occurences) for characters. Thus, the Character array size would never be too long and we achieve what we need.

Advantage: Single iteration over the input string's characters. Character array size never grows to high limits. Result map contains occurences for each character.

Cheers

Answer 5

You could do that with Regular Expressions:

Pattern pattern = Pattern.compile("[\\(\\)]"); //Pattern says either '(' or ')'
Matcher matcher = pattern.matcher("(Yeahhhh) I have finally made it to the (top)");
int count = 0;
while (matcher.find()) { //call find until nothing is found anymore
  count++;
}
System.out.println("count "+count);

The Pro is, that the Patterns are very flexible. You could also search for embraced words: "\\(\\w+\\)" (A '(' followed by one or more word characters, followed by ')')

The Con is, that it may be like breaking a fly on the wheel for very simple cases

See the Javadoc of Pattern for more details on Regular Expressions