nextBytes(byte bytes) – fills the specified byte array with random bytes.nextDouble() – returns a random double number greater than or equal to 0.0 and less than 1.0 (this method is called from Math.random(), as described in the previous section).nextFloat() – returns a random float number greater than or equal to 0.0 and less than 1.0.nextBoolean() – returns a random boolean value, i.e., true or false.nextLong() – generates a random long value.nextInt(int bound) – generates a random number greater than or equal to 0 and less than the specified upper bound.Other methods for generating random values are: Int i = random.nextInt() Code language: Java ( java ) With it, you can generate a random int number as follows: Random random = new Random() Java Random ClassĪlso present since Java 1.0 is the class. Internally, Math.random() calls the nextDouble() method of a static instance of the Random class held in the Math class, which is discussed in the next section.įor more details on Math.random()'s internal functionality and thread safety, see the chapter on implementing this method. If you work with one of these versions, you must not call Math.random() from different threads. However, synchronization is broken from Java 1.3 up to and including Java 7. Math.random() is thread-safe according to the documentation. More precisely: a double floating-point number greater than or equal to 0.0 and less than 1.0. The call returns a random number between 0 and 1. One of the oldest methods (it has existed since Java 1.0) to generate a random double number is to call Math.random(): double d = Math.random() Code language: Java ( java ) This chapter shows the fundamental classes and methods for generating a random number in Java and what to consider when using them in terms of thread safety. You can find the code samples for this article in this GitHub repository. and how the implementation of the various methods has changed throughout Java versions.Įxperienced Java developers familiar with the various ways to create random values can skip directly to the "Pseudorandom Number Generation" or "Changes in Implementations Over Time" section.
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