weixin_40436179
野原新之楠
2019-04-06 15:53

Java 关于如何override hashcode的问题

  • java
  • intellij-idea
  • eclipse

3个练习里分别要定义3中ADT(abstract data type)
1. FList (定义一个list)
2. FSet (定义一个set)
3. FMap(定义一个map)

在改写hashcode时候遇到了困难。前两个练习没有做关于hashcode的说明
我直接 return FList.size() 和 FSet.size() ps:我知道这样不对。。。。。

第3个练习里有了规定 瞬间不懂了。。。

If m1 and m2 are values of the FMap ADT, and

    ! (m1.equals(m2))



then m1.hashCode() is unlikely to be equal to m2.hashCode().

Note: The word "unlikely" will be interpreted as follows. For every type K and V, if both m1 and m2 are selected at random from a set of FMap values such that for every non-negative integer n and int value h the probability of a randomly selected FMap m having

n == m.size() is

P(n) = 1/(2^(n+1))

and for each key k such that m.containsKey(k) the probability that

     h == k.hashCode() is at most 1/5

and for each value v such that v.equals(m.get(k)) the probability that

     h == v.hashCode() is at most 1/5

and the three probabilities above are independent

then the probability of m1.hashCode() == m2.hashCode() when m1 and m2 are not equal is less than 40%.

这里面是要求我设计hashcode m1和m2相等概率小于40%?

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