java random seed 使用

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        Random random = new Random(50);
        for (int j = 0; j < 8; j++) {
            System.out.print(" " + random.nextInt(100) + ", ");
        }
        System.out.println();
        for (int j = 0; j < 8; j++) {
            System.out.print(" " + random.nextInt(100) + ", ");
        }
        System.out.println();
        Random random2 = new Random(50);
        for (int j = 0; j < 8; j++) {
            System.out.print(" " + random2.nextInt(100) + ", ");
        }
        System.out.println();
        for (int j = 0; j < 8; j++) {
            System.out.print(" " + random2.nextInt(100) + ", ");
        }
        System.out.println();

        System.out.println("-----------------------------------");
        Random random3 = new Random();
        for (int j = 0; j < 8; j++) {
            System.out.print(" " + random3.nextInt(100) + ", ");
        }
        System.out.println();
        Random random4 = new Random();
        for (int j = 0; j < 8; j++) {
            System.out.print(" " + random4.nextInt(100) + ", ");
        }
        System.out.println();

 17,  88,  93,  12,  51,  61,  36,  58, 
 16,  8,  0,  12,  0,  55,  28,  92, 
 17,  88,  93,  12,  51,  61,  36,  58, 
 16,  8,  0,  12,  0,  55,  28,  92, 
-----------------------------------
 5,  15,  5,  57,  89,  12,  54,  74, 
 95,  3,  95,  96,  23,  77,  57,  62, 

带种子的随机数生成器，每次生成的随机数可能不同；但每一遍生成的随机数是相同的；

不带种子的随机数生成器每次生成的随机数可能不同；但每一遍生成的随机数也可能不同；

    /**
     * Creates a new random number generator. This constructor sets
     * the seed of the random number generator to a value very likely
     * to be distinct from any other invocation of this constructor.
     */
    public Random() {
        this(seedUniquifier() ^ System.nanoTime());
    }

  /**
     * Creates a new random number generator using a single {@code long} seed.
     * The seed is the initial value of the internal state of the pseudorandom
     * number generator which is maintained by method {@link #next}.
     *
     * <p>The invocation {@code new Random(seed)} is equivalent to:
     *  <pre> {@code
     * Random rnd = new Random();
     * rnd.setSeed(seed);}</pre>
     *
     * @param seed the initial seed
     * @see   #setSeed(long)
     */
    public Random(long seed) {
        if (getClass() == Random.class)
            this.seed = new AtomicLong(initialScramble(seed));
        else {
            // subclass might have overriden setSeed
            this.seed = new AtomicLong();
            setSeed(seed);
        }
    }

    private static long initialScramble(long seed) {
        return (seed ^ multiplier) & mask;
    }

    /**
     * Sets the seed of this random number generator using a single
     * {@code long} seed. The general contract of {@code setSeed} is
     * that it alters the state of this random number generator object
     * so as to be in exactly the same state as if it had just been
     * created with the argument {@code seed} as a seed. The method
     * {@code setSeed} is implemented by class {@code Random} by
     * atomically updating the seed to
     *  <pre>{@code (seed ^ 0x5DEECE66DL) & ((1L << 48) - 1)}</pre>
     * and clearing the {@code haveNextNextGaussian} flag used by {@link
     * #nextGaussian}.
     *
     * <p>The implementation of {@code setSeed} by class {@code Random}
     * happens to use only 48 bits of the given seed. In general, however,
     * an overriding method may use all 64 bits of the {@code long}
     * argument as a seed value.
     *
     * @param seed the initial seed
     */
    synchronized public void setSeed(long seed) {
        this.seed.set(initialScramble(seed));
        haveNextNextGaussian = false;
    }

以上基于java1.8

随机数是种子经过计算生成的。

• 不含参的构造函数每次都使用当前时间作为种子，随机性更强
• 而含参的构造函数其实是伪随机，更有可预见性