Creating a new Random
object each time a random value is needed is inefficient and may produce numbers which are not random depending
on the JDK. For better efficiency and randomness, create a single Random
, then store, and reuse it.
The Random()
constructor tries to set the seed with a distinct value every time. However there is no guarantee that the seed will be
random or even uniformly distributed. Some JDK will use the current time as seed, which makes the generated numbers not random at all.
This rule finds cases where a new Random
is created each time a method is invoked and assigned to a local random variable.
public void doSomethingCommon() { Random rand = new Random(); // Noncompliant; new instance created with each invocation int rValue = rand.nextInt(); //...
private Random rand = SecureRandom.getInstanceStrong(); // SecureRandom is preferred to Random public void doSomethingCommon() { int rValue = this.rand.nextInt(); //...
A class which uses a Random
in its constructor or in a static main
function and nowhere else will be ignored by this
rule.