Why not use random

Standard JDK implementations of java.util.Random use a Linear Congruential Generator (LCG) algorithm for providing random numbers. The problem with this algorithm is that it’s not cryptographically strong. In other words, the generated values are much more predictable, therefore attackers could use it to compromise our system.

Random and Secure Random

Random r1 = new Random(165);
 Random r2 = new Random(165);

int n ,n2;

for (int i = 0; i < 5; i++) {
    n = r1.nextInt();
    n2 = r2.nextInt();
    System.out.println(n + " " + n2);
}
Output -> 
-1120472427 -1120472427
1501130588 1501130588
-807469490 -807469490
-1259549308 -1259549308
-1115179331 -1115179331

as you can see Pseudo-random gives us the same values

Now let’s try the same work with SecureRandom

byte[] s = new byte[] { (byte) 0xA5 };
SecureRandom sr1 = new SecureRandom(s);
SecureRandom sr2 = new SecureRandom(s);
if(sr1.nextInt() == sr2.nextInt()) {
    System.out.println("Same seed");
} else {
    System.out.println("Different seed");
}
Output -> Different seed