[英]add ArrayList to multiple ArrayList in java
Hi i have problem with ArrayLists i have 3 lists 嗨,我有ArrayLists的问题,我有3个列表
ArrayList1<Integer>=[1,2,3]
ArrayList2<Integer>=[]
ArrayList3<ArrayList<Integer>>=[]
ArrayList1 elements are used for adding values to ArrayList2 for example ArrayList1元素用于向ArrayList2添加值
for(int i:ArrayList1)
{
for(int a=0;a<i;a++)
{
ArrayList2.add(a);
}
}
and that works fine no problem there but now i want to for every element in ArrayList1 to add ArrayList2 to ArrayList3 this is what I have come up with but it does not work 并且工作正常,没有问题,但是现在我想为ArrayList1中的每个元素添加ArrayList2到ArrayList3,这是我想出的,但它不起作用
for(int i:ArrayList1)
{
for(int a=0;a<i;a++)
{
ArrayList2.add(a);
}
ArrayList3.add(ArrayList2);
}
Simply use addAll
, and Collections.fill
. 只需使用
addAll
和Collections.fill
。
Example 例
list2.addAll(list1);
list3 = new ArrayList<ArrayList<Integer>>(list1.size());
Collections.fill(list3, list2);
Note that list3
will be filled with the same instance of list2
. 请注意,
list3
将使用相同的list2
实例填充。
This means that every change to list2
will be reflected in each element of list3
. 这意味着对
list2
每次更改都会反映在list3
每个元素中。
If this is not the behavior you're expecting, iterate over the length of list1
and add a new ArrayList<Integer>(list2)
. 如果这不是您期望的行为,请遍历
list1
的长度并添加一个new ArrayList<Integer>(list2)
。
for(int a=0;a<i;a++)
is wrong. 是错的。 You must not stop at
a < i
, it makes no sense! 您一定不要在
a < i
处停下来,这没有任何意义! You want to add the whole arrayList2 to ArrayList3, not a number of integers equal to the value of the int i in ArrayList1. 您想将整个arrayList2添加到ArrayList3,而不是等于ArrayList1中int i值的整数。
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