Java 将 ArrayList 中的所有整数元素加 1
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Increment all integer elements by 1 in a ArrayList
提问by Sravan2023
I need to increment the values for certain part of a ArrayList by a given number.
我需要按给定数字增加 ArrayList 某些部分的值。
like [ 1 2 3 4 5 6 7 8 9 1 1 1 ]lets say i need to increment last 3 elements by 2
so that the result would be
像[ 1 2 3 4 5 6 7 8 9 1 1 1 ]可以说，我需要通过2递增最后3个元素，这样的结果将是
[ 1 2 3 4 5 6 7 8 9 3 3 3 ]
how can i do this ?
我怎样才能做到这一点 ？
采纳答案by Erik Kaplun
Assuming arrayListcontains the ArrayList<Integer>instance:
假设arrayList包含ArrayList<Integer>实例：
int startFrom = arrayList.size() - 3;
int upTo = arrayList.size();
int incrBy = 2;
for (int i = startFrom; i < upTo && i < arrayList.size(); i += 1) {
int oldValue = arrayList.get(i);
int newValue = oldValue + incrBy;
arrayList.set(i, newValue);
}
or, more compactly (i.e. inlining the variables oldValueand newValue):
或者，更简洁（即内联变量oldValue和newValue）：
for (int i = startFrom; i < upTo && i < arrayList.size(); i += 1) {
arrayList.set(i, arrayList.get(i) + incrBy);
}
回答by Ravi Thapliyal
Hint :ArrayListprovides indexed access to its members. You can easily loop over the required elements. For incrementing last nelements make use of a forloop and list's size().
提示：ArrayList提供对其成员的索引访问。您可以轻松地遍历所需的元素。为了增加最后一个n元素，请使用for循环和列表的size().
回答by MaD
Assuming that the part that needed to be incremented in known [from, to]. You just loop on the ArrayList and add the number you wish: (remember that you can access the items in the ArrayList by index)
假设需要在已知[from, to] 中递增的部分。您只需在 ArrayList 上循环并添加您想要的数字：（请记住，您可以通过索引访问 ArrayList 中的项目）
arr - is ArrayList
arr - is ArrayList
number- is the number you wish to increment by
number- 是您希望增加的数字
for (int i = from; i < to; i++){
int item = arr.get(i);
arr.set(i,item+number);
}
- I assume here that
fromandtoare valid indexes for the ArrayList but you should always check if they are within the array bounds
- 我这里假设
from和to是ArrayList的有效指标，但您应经常检查，如果他们是在阵列范围内
