HackersEarth - Reverse primes
Just a simple idea: From each pair, you generate both the smaller and the bigger prime. You're using a Set in order to assure that you don't output both. But this can be done much simpler:

Instead of

            long revrse = reversePrime(prime);
            if ((!(prime == revrse))
                    &amp;&amp; (!reversedCheckedPrime.contains(revrse))
                    &amp;&amp; (reversedCheckedPrime.size() &lt;= MAXLISTSIZE)) {
                reversedCheckedPrime.add(prime);
            }


use

            long revrse = reversePrime(prime);
            if (prime &lt; revrse) {
                reversedCheckedPrime.add(prime);
            }


You simply add the smaller one only (which also handles the case of -self-reversed numbers). The test

 reversedCheckedPrime.size() &lt;= MAXLISTSIZE


was both wrong (should be &lt;) and useless (as there's a break later).

Now you can replace the Set by a List and gain some speed. You can gain even more, if you use a long[] of length MAXLISTSIZE (which should be called MAX_LIST_SIZE) as you avoid autoboxing.