"FooBar".includes("oo"); // true

"FooBar".includes("foo"); // false

"FooBar".includes("oo", 2); // false

if (your_string.indexOf('hello') > -1)
{
  alert("hello found inside your_string");
}

public static boolean containsIgnoreCase(String str, char c) {
        str = str.toLowerCase();

        for (int i = 0; i < str.length(); i++) {
            if (str.charAt(i) == Character.toLowerCase(c)) {
                return true;
            }
        }
        
        return false;
    }