Collections. Instance parsing of shuffle () method

This paper mainly studies collections Shuffle () method. Let's see the details below.

Java. util. There is a static shuffle () method under the collections class, as follows:

1) Static void shuffle (list list) uses the default random source to replace the list. All replacement possibilities are approximately equal.

2) Static void shuffle (list list, random Rand) replaces the specified list with the specified random source. The probability of all substitutions is approximately equal. It is assumed that the random source is fair.

Generally speaking, it's like shuffling cards, randomly disrupting the original order.

Note: if an integer array is given, use arrays The aslist () method converts it into a collection class in two ways:

1) Use list < integer > List = ArrayList (arrays. Aslist (IA)), and shuffle () will not change the order of the underlying array.

2) Use list < integer > List = arrays Aslist (IA), and then shuffle () will change the order of the underlying array. Code examples are as follows:

The operation results are as follows:

In the first case, arrays The output of aslist () is passed to the constructor of ArrayList (), which will create an ArrayList that references the elements of IA, so disrupting these references will not modify the array. However, if you directly use arrays As a result of aslist (IA), this disorder will modify the order of IA. It is important to realize that the list object generated by arrays. Aslist () will use the underlying array as its physical implementation. As long as the operation you perform will modify the list and you don't want the original array to be modified, you should create a copy in another container.

summary

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