将 3 个数组列表合并为一个

使用 ArrayList.addAll（）。像这样的东西应该有效（假设列表包含对象;你应该相应地改变）。String

List<String> combined = new ArrayList<String>();
combined.addAll(firstArrayList);
combined.addAll(secondArrayList);
combined.addAll(thirdArrayList);

更新

从您的评论中可以看出，您实际上可能正在尝试创建2D列表。如果是这样，如下所示的代码应该可以正常工作：

List<List<String>> combined2d = new ArrayList<List<String>>();
combined2d.add(firstArrayList);
combined2d.add(secondArrayList);
combined2d.add(thirdArrayList);

使用java.util.Arrays.asList来简化合并怎么样？

List<String> one = Arrays.asList("one","two","three");
List<String> two = Arrays.asList("four","five","six");
List<String> three = Arrays.asList("seven","eight","nine");

List<List<String>> merged = Arrays.asList(one, two, three);