如何正确创建ArrayLists的ArrayList? [英] How to correctly create an ArrayList of ArrayLists?

问题描述

我正在尝试创建一个ArrayLists的ArrayList.我想创建25个ArrayList，并让这些ArrayList拥有不同的值.目的是创建按字长排序的字典.

I am trying to create an ArrayList of ArrayLists. I want to create 25 ArrayLists and have those ArrayList hold different values. The goal being to create a sorted dictionary by word length.

我的代码看起来像

    for(int i = 0; i < 25; i++)
         list2D.add(list);
    for(int i = 0; i < stringList; i++)
         list2D.get(stringList.get(i).length()).add(stringList.get(i))

问题在于，每个列表在完成后都包含相同的值.

The problem is that every list contains the same values after it finishes.

我知道为什么会这样. 列表"是一个ArrayList，ArrayList是对象，如果您编辑一个对象，则包含该对象的所有内容都会被编辑.

I know why the problem is happening. "list" is an ArrayList, ArrayList's are objects and if you edit an object then everything containing that object will be edited.

要解决我尝试过的问题

    for(int i = 0; i < 25; i++){
        list = new ArrayList<String>();
        for(int i2 = 0; i2 < stringList.size(); i2++){
            if(stringList.get(i).length() == i)
                list.add(stringList.get(i2));
        }
        list2D.add(list);
    }

但是当我测试我的"list2D"

But when I test my "list2D"

    for(int i = 0; i < 25; i++)
         System.out.print(list2D.get(i).size()+" ");

我知道

0 0 0 0 0 58110 0 58110 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 58110 0 58110 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

我不知道为什么...

and I have no idea why...

另外，可能有必要注意stringList包含58110个值.

Also it might be relevant to note that stringList contains 58110 values.

我也不想创建25个不同的ArrayList！

Also I don't want to have to make 25 different ArrayLists!

推荐答案

我将尝试以下操作对stringList进行一次遍历

I would try the following to do a single pass of the stringList

List<List<String>> dict = new ArrayList<>();
for(string s: stringsList) {
    int len = s.length();
    // add new array lists as required, could be any length, assuming << 100
    while(dict.size() <= len) dict.add(new ArrayList<String>());
    // add the string to the right list.
    dict.get(len).add(s);
}

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