====== java Random ======
  * [[https://docs.oracle.com/en%2Fjava%2Fjavase%2F21%2Fdocs%2Fapi%2F%2F/java.base/java/util/Random.html|java.util.Random]]
  * 랜덤 값 생성.
  * see [[https://docs.oracle.com/en%2Fjava%2Fjavase%2F21%2Fdocs%2Fapi%2F%2F/java.base/java/util/concurrent/ThreadLocalRandom.html|java.util.concurrent.ThreadLocalRandom]]
  * [[https://docs.oracle.com/en%2Fjava%2Fjavase%2F21%2Fdocs%2Fapi%2F%2F/java.base/java/security/SecureRandom.html|java.security.SecureRandom]]

===== 주의 =====
  * ''java.util.Raandom''은 Thread Safe 하다.
  * 하지만 대신 공유해서 사용할 경우 ''synchronized''로 인해 성능이 매우 떨어진다.
  * 가급적 [[https://docs.oracle.com/en%2Fjava%2Fjavase%2F21%2Fdocs%2Fapi%2F%2F/java.base/java/util/concurrent/ThreadLocalRandom.html|java.util.concurrent.ThreadLocalRandom]] 을 사용한다.

<note warning>
Instances of java.util.Random are threadsafe. However, the concurrent use of the same java.util.Random instance across threads may encounter contention and consequent poor performance. Consider instead using ThreadLocalRandom in multithreaded designs. 
</note>