如何创建二维数组列表? [英] How to create a 2D ArrayList?

问题描述

我正在尝试使用 Java 创建一个二维数组.行的大小是已知的，而列的大小是未知的.这是我的代码，但它不起作用.谁能给我一些想法?

I'm trying to use Java to create a 2-dimensional array. The size of rows is known, while the size of columns is unknown. Here is my code and it doesn't work. Could anyone give me some idea?

ArrayList<Integer> paths[];
paths = new ArrayList[2]；// 2 paths
for (int i=0; i<2; ++i)
    paths[i].add(1); // add an element to each path

推荐答案

在添加之前初始化数组元素.将初始化放入 for 循环中:

Initialize the array element before adding to it. Put the initialization into the for loop:

@SuppressWarnings("unchecked")
ArrayList<Integer>[] paths = new ArrayList[2];

for (int i=0; i<2; ++i) {
    paths[i] = new ArrayList<Integer>();
    paths[i].add(1);
}

这样可以避免NullPointerException.

这篇关于如何创建二维数组列表?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！