Java 你如何创建一个整数 ArrayList？
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How do you create an integer ArrayList?
提问by Tomek
I am trying to create an array of Arraylists in Java. I have declared it in the following way:
我正在尝试用 Java 创建一个数组列表。我已通过以下方式声明它：
ArrayList[][][] arrayQ = new ArrayList[90][13][18];
for (int i = 0; i < 90; i++) {
for (int j = 0; j < 13; j++) {
for (int k = 0; k < 18; k++) {
arrayQ[i][j][k] = new ArrayList<int>();
}
}
}
However, adding the <int>inside the while loop throws an error (the IDE I'm using unfortunately doesn't give me a very good error message).
但是，<int>在 while 循环中添加内部会引发错误（不幸的是，我正在使用的 IDE 并没有给我一个很好的错误消息）。
What's the proper way to create an integer ArrayList?
创建整数 ArrayList 的正确方法是什么？
回答by joschi
回答by Andy White
It looks like you're mixing the non-generic and generic ArrayLists. Your 3D array of ArrayListuses the non-generic, but you are trying to assign a generic ArrayList<int>. Try switching one of these to match the other.
看起来您正在混合 non-generic 和 generic ArrayLists。您的 3D 数组ArrayList使用非泛型，但您正在尝试分配泛型ArrayList<int>. 尝试切换其中一个以匹配另一个。
回答by Andy Dvorak
joschi and Cristian are correct. Change new ArrayList<int>()to new ArrayList<Integer>()and you should be fine.
joschi 和 Cristian 是正确的。更改new ArrayList<int>()到new ArrayList<Integer>()，你应该罚款。
If at all possible, I would recommend using Eclipseas your IDE. It provides (usually) very specific, detailed, and generally helpful error messages to help you debug your code.
如果可能的话，我建议使用Eclipse作为您的 IDE。它提供（通常）非常具体、详细且通常有用的错误消息，以帮助您调试代码。
回答by EboMike
The problem is that an ArrayListrequires Objects- you cannot use primitive types.
问题是ArrayList需要Objects- 您不能使用原始类型。
You'll need to write arrayQ[i][j][k] = new ArrayList<Integer>();.
你需要写arrayQ[i][j][k] = new ArrayList<Integer>();.
回答by robertmoggach
Here's a complete example:
这是一个完整的例子：
ArrayList<Integer>[] foo = new ArrayList[3];
foo[0] = new ArrayList<Integer>();
foo[1] = new ArrayList<Integer>();
foo[2] = new ArrayList<Integer>();
foo[0].add(123);
foo[0].add(23);
foo[1].add(163);
foo[1].add(23789);
foo[2].add(3);
foo[2].add(2);
for (ArrayList<Integer> mylist: foo) {
for (int bar : mylist) {
println(bar);
}
}
