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The java. util. Random. nextBytes() method generates random bytes and provides it to the user defined byte array.
rand(): rand() function is a predefined method of C++. It is declared in <stdlib. h> header file. rand() is used to generate random number within a range.
If we want to determine the size of array, means how many elements present in the array, we have to write calculation with the help of sizeof() operator. Sizeof(arr[]) / sizeof(arr[0]) ; Here, the size of arr[] is 5 and each float takes memory 8 bytes. So, the total memory is consumed = (5 * 8) bytes.
random_bytes(int $length ): string. Generates an arbitrary length string of cryptographic random bytes that are suitable for cryptographic use, such as when generating salts, keys or initialization vectors.
Try the Random.nextBytes method:
byte[] b = new byte[20];
new Random().nextBytes(b);
If you want a cryptographically strong random number generator (also thread safe) without using a third party API, you can use SecureRandom.
Java 6 & 7:
SecureRandom random = new SecureRandom();
byte[] bytes = new byte[20];
random.nextBytes(bytes);
Java 8 (even more secure):
byte[] bytes = new byte[20];
SecureRandom.getInstanceStrong().nextBytes(bytes);
If you are already using Apache Commons Lang, the RandomUtils makes this a one-liner:
byte[] randomBytes = RandomUtils.nextBytes(20);
Note: this does not produce cryptographically-secure bytes.
Java 7 introduced ThreadLocalRandom which is isolated to the current thread.
This is an another rendition of maerics's solution.
final byte[] bytes = new byte[20];
ThreadLocalRandom.current().nextBytes(bytes);
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