hashcode的实现

1. ThinkinJava中给出了Effective Java的实现。
1. 给出int变量result赋予某个非零值常量，例如17.
2. 为对象内每个有意义的域f（即每个可以坐equals()操作的域）计算一个int的码c：
1. boolean --- c=(f?0:1)
2. byte, char, short, int --- c=(int)f
3. long --- c = (int) (f ^ (f >>> 32))
4. float --- c = Float.floatToIntBits(f);
5. double --- long l Double.doubleToLongBits(f); c = (int) (l ^ l >>>32))
6. Object --- c=f.hashCode()
7. Array --- every element do it.
3. result = 37 * result + c；