java - 请问这个变量如何初始化？

Question

初学java。

 ArrayList<Integer>[] g;

Answer 1

If you want to create an ArrayList array, you can write it like this

ArrayList<Integer>[] array = new ArrayList[3];
        System.out.println(array.length);

Answer 2

I also suspect[]符号多加了，你应该不会是要一个list的数组。
那么，ArrayList<Integer> g = new ArrayList<Integer>();如果list的大小确认，可写成：ArrayList<Integer> g = new ArrayList<Integer>(size);Generally, there is no need to specify it. The performance impact is not significant and can be completely ignored.

Answer 3

Hello! It is recommended to learn more about Java. ArrayList is originally a collection. A collection can be seen as a dynamic array, so there is no need to add [] at the end.

ArrayList<Integer> g = new ArrayList<Integer>(0);

Answer 4

ArrayList<Integer>[] array = new ArrayList<Integer>[Integer.MAX_VALUE];