英文:
Passing in type of elements in collection to a function which initialises an ArrayList (Java)?
问题
我想要一个函数，该函数接受一个参数，然后将 E 设置为 ArrayList 中的元素类型，其中 E 是此集合中的元素类型。因此，展示我想要实现的最简代码如下，其中 E 是我不知道的内容。
private void createArray(E dataType) {
ArrayList<E> list = (ArrayList<E>) message.getArray();
}
这是否可能？我尝试查看 ArrayList 类以找到答案，但我对 Java 不太熟悉。
编辑：
我不确定我的问题是否足够清楚... 我不需要传递变量 dataType。我需要变量 dataType 成为我在初始化 ArrayList 时输入 <> 中的内容。我找到了以下答案：https://stackoverflow.com/questions/42069745/pass-class-type-as-parameter-to-use-in-arraylist，但对我并没有太大帮助。我需要使用数组列表中的元素并调用仅适用于该类的方法...
private <T> void createModel(String SQLcomm, Class<T> dataType, DefaultTableModel table) {
Parcel parc = SQLtask(SQLcomm, "array");
ArrayList<T> list = (ArrayList<T>) parc.getData();
for (T t : list) {
Vector<Object> newRow = t.getinfo(); //无法执行 t.getinfo() 吗？
table.addRow(newRow);
}
}
英文:
I would like a function which takes in a parameter that then sets E in the ArrayList where E is the type of elements in this collection. So the simplest code showing what I want to do is as such, where E is what I don't know.
private void createArray(E dataType) {
ArrayList<dataType> list = (ArrayList<dataType>) message.getArray();
}
Is this at all possible? I tried to find an answer by looking at the ArrayList class but I don't have much experience with Java.
Edit:
I am not sure if my question is clear enough... I don't need to pass the variable dataType. I need the variable dataType to be what goes into <> when I do the line where I initialise the ArrayList. I have found the following answer: https://stackoverflow.com/questions/42069745/pass-class-type-as-parameter-to-use-in-arraylist but it doesn't really work for me. I need to use the elements in the arraylist and call a method which only applies to that class...
private <T> void createModel(String SQLcomm, Class<T> dataType, DefaultTableModel table) {
Parcel parc = SQLtask(SQLcomm, "array");
ArrayList<T> list = (ArrayList<T>) parc.getData();
for (T t: list) {
Vector<Object> newRow = t.getinfo(); //can't do t.getinfo()?
table.addRow(newRow);
}
答案1
得分: 0
一个数组不是ArrayList。但你可以使用如下方法：
如果你有一个数组，你可以使用：
Arrays.asList(array);
否则：
List<E> list = new ArrayList<>();
list.add(element);
希望这回答了你的问题。
英文:
An array isn't an ArrayList. But you can use something that method:
If you have an array you can use:
Arrays.asList(array);
Otherwise:
List<E> list = new ArrayList<>();
list.add(element);
I hope this answers your question.
答案2
得分: 0
当然是“可能的” - 你可以这样编写：
private <E> void createArray(E dataType) {
ArrayList<E> list = (ArrayList<E>) message.getArray();
}
英文:
Sure it's "possible" - you can write:
private <E> void createArray(E dataType) {
ArrayList<E> list = (ArrayList<E>) message.getArray();
}
答案3
得分: 0
你可以这样做，但是你必须将数据类型作为类参数传递，这在Java中称为泛型（有关泛型的更多信息，请参阅官方Java文档中的[链接][1]）
示例：
// E 为你的数据类型
public class A<E> {
// 可能从数据库获取数据（ResultSet）
public void createArray(ResultSet message, String index) throws SQLException {
ArrayList<E> list = (ArrayList<E>) message.getArray(index);
// 其余代码...
}
}
有关处理数组的更多信息，请参阅[此处][2]的官方文档。
[1]: https://docs.oracle.com/javase/tutorial/java/generics/types.html
[2]: https://docs.oracle.com/javase/tutorial/jdbc/basics/array.html
英文:
You can, but you have to pass the data type as a class parameter, this is called genericity in java (for more info on genericity, here is a link to the official java doc)
Example :
// E your data type
public class A<E> {
//Maybe you get data from database (ResultSet)
public void createArray(ResultSet message, String index) throws SQLException {
ArrayList<E> list = (ArrayList<E>) message.getArray(index);
//the rest of the code...
}
}
For more info on handling arrays here is the official doc.
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