访问ArrayList& lt; ArrayList& SomeObject& gt;元素 [英] Accessing ArrayList<ArrayList<SomeObject>> elements

问题描述

我有一个 ArrayList 的 ArrayList ，在这里我需要找到一种访问元素的简单方法，以使其更易于理解，我已经制定了我的目标我想实现:

I have an ArrayList of ArrayLists where i need to find a simple way of accessing the elements, to make it easier to understand i have drawn my goal of what i want to achieve:

在主 ArrayList 上方的图像中看到，由 m ArrayList 组成，我希望使用来获取元素> get 方法，它从0到 N 个元素，其中 N 是 ArrayList1 和 ArrayList2 .可能会出现更多的ArrayList.

As seen on the image above the main ArrayList consists of m ArrayList, where i wish to get an element by using a get method which goes from 0 to N elements, where N is the total elements of ArrayList1 and ArrayList2. More ArrayList's may occur.

我当然可以通过使用两个for循环来遍历元素，在这种情况下，这不是我要搜索的.

I can of course iterate through the elements by using two for-loops, which is not what im searching for in this case.

推荐答案

您基本上需要在新包装器类上具有 ArrayList 成员，并以不同的方式实现它们.我整理了一个示例，演示了在 get()中计算出的正确索引.

You would need to basically have the the ArrayList members on your new wrapper class and implement them in a different manner. I whipped up an example that demonstrates the correct index being calculated in get().

import java.util.ArrayList;

public class ListHolder<T> {
    public ArrayList<ArrayList<T>> list = new ArrayList<ArrayList<T>>();

    public int size() {
        int size = 0;
        for (int i = 0; i < list.size(); i++) {
            size += list.get(i).size();
        }
        return size;
    }

    public T get(int i) {
        if (i >= size())
            return null;

        int listIndex = 0;
        int valueIndex = i;

        while (valueIndex >= list.get(listIndex).size()) {
            valueIndex -= list.get(listIndex++).size();
        }

        return list.get(listIndex).get(valueIndex);
    }
}

我用来验证我的方法的内容:

What I used to verify my methods:

public static void main(String[] args)
{
    ListHolder<Object> listHolder = new ListHolder<Object>();

    listHolder.list.add(new ArrayList<Object>());
    listHolder.list.get(0).add("hello");
    listHolder.list.get(0).add("world");

    listHolder.list.add(new ArrayList<Object>());
    listHolder.list.get(1).add("a");
    listHolder.list.get(1).add("b");
    listHolder.list.get(1).add("c");

    System.out.println("Size: " + listHolder.size());
    System.out.println("listHolder[0]: " + listHolder.get(0)); // "hello"
    System.out.println("listHolder[1]: " + listHolder.get(1)); // "world"
    System.out.println("listHolder[2]: " + listHolder.get(2)); // "a"
    System.out.println("listHolder[3]: " + listHolder.get(3)); // "b"
    System.out.println("listHolder[4]: " + listHolder.get(4)); // "c"
    System.out.println("listHolder[5]: " + listHolder.get(5)); // "null"
}

这篇关于访问ArrayList& lt; ArrayList& SomeObject& gt;元素的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！