Java Random contains the difference between participating in a non-parametric constructor

# #Random is commonly used as a random number generator, it has two construction methods:

        Random random = new Random();        Random random2 = new Random(50);

1. No parameter construction method:

public Random() {    setSeed(System.nanoTime() + seedBase);    ++seedBase;}

2. Construction method with parameters:

public Random(long seed) {    setSeed(seed);}

The Setseed method is called:

public synchronized void setSeed(long seed) {    this.seed = (seed ^ multiplier) & ((1L << 48) - 1);    haveNextNextGaussian = false;}

# # #可以看到, the non-parametric construction method uses the current time as a seed each time, and the method with the parameter construction is a fixed value as the seed

# #什么是种子 seed?

Seed is the parameter used when random numbers are generated:

The most important thing in Random is the next (int) method, which is calculated using seed:

protected synchronized int next(int bits) {    seed = (seed * multiplier + 0xbL) & ((1L << 48) - 1);    return (int) (seed >>> (48 - bits));}

The other nextxxx methods are called Next ().

such as Nextint (int):

public int nextInt(int n) {    if (n <= 0) {        throw new IllegalArgumentException("n <= 0: " + n);    }    if ((n & -n) == n) {//调用 next()        return (int) ((n * (long) next(31)) >> 31);    }    int bits, val;    do {        bits = next(31);        val = bits % n;    } while (bits - val + (n - 1) < 0);    return val;}

Again such as Nextboolean ():

//也是调用的 next()public boolean nextBoolean() {    return next(1) != 0;}

# #举个栗子:

@Testpublic void testRandomParameter(){    System.out.println("Random 不含参构造方法：");    for (int i = 0; i < 5; i++) {        Random random = new Random();        for (int j = 0; j < 8; j++) {            System.out.print(" " + random.nextInt(100) + ", ");        }        System.out.println("");    }    System.out.println("");    System.out.println("Random 含参构造方法：");    for (int i = 0; i < 5; i++) {        Random random = new Random(50);        for (int j = 0; j < 8; j++) {            System.out.print(" " + random.nextInt(100) + ", ");        }        System.out.println("");    }}

The 5 random generator objects are created by using the method of constructing with the parameter and without the parameter, and each random generator reproduces 8 random numbers, and compares the results:

Run once more:

# #总结:

From the above examples, we can find:

A random number is a seed that is generated by calculation.

• Constructors with no parameters use the current time as a seed each time, more randomness
• The constructors with parameters are pseudo-random and more predictable.

Java Random contains the difference between participating in a non-parametric constructor