java: How to check StringBuilder charcters to see if it contains same characters as new string request from array?

Question

I want to check if a Java StringBuilder object contains a character.

For example I have a list of foods in an array {apple, pear, orange, peach, cherry} and I want to add a random number of these food types to the StringBuilder.

How would I check if StringBuilder contains a character?

Answer 1

The StringBuilder class does not have a contains() method, but it does have an indexOf() method. The indexOf() method returns -1 when the substring was not found.

Example:

stringBuilder.indexOf(charactersYouWantToCheck)!=-1 

Answer 2

The StringBuilder class does not have a contains() method, but String does. So you can use StringBuilder to build a string by using toString(). Then call contains() on it, to check if it contains that character or string.

Example:

stringBuilder.toString().contains(characterYouWantToCheck) 

Answer 3

It is of course possible to check the string by iterating through it (e.g. use indexOf()), but I would use a Set in this particular instance to add the fruits (if it already exists it will not be added again), once you're done adding fruits convert the Set into a String, e.g.

Set<String> fruits = new HashSet<String>();
for (String fruit: fruitSource) {
    fruits.add(fruit);
}
StringBuilder sb = new StringBuilder();
for (String fruit: fruits) {
    sb.append(fruit);
    sb.append(", ");
}
return sb.toString();

Answer 4

A different option is to create a List<String> of all of the options, and use Collections.shuffle to randomly permute the list. You can then join together the first n elements.

Since both Collections.shuffle and joining together the first n elements takes linear time, the entire process should take linear time.