英文:
Is there a way to keep the ArrayList as a local variable?
问题
public static ArrayList<String> searchFiles(File currentFolder) throws NotDirectoryException {
ArrayList<String> result = new ArrayList<String>();
if (!currentFolder.isDirectory())
throw new NotDirectoryException("File is not a directory");
File[] direct = currentFolder.listFiles();
if (direct != null) {
for (int i = 0; i < direct.length; i++) {
if (direct[i].isDirectory())
searchFiles(direct[i]);
if (direct[i].isFile() && !direct[i].isHidden())
result.add(direct[i].getName());
}
}
return result;
}
这段代码的目的是递归地搜索所有目录和子目录，然后将符合条件的文件添加到一个 ArrayList 中。如果将 ArrayList 声明从方法中移除，改为作为全局变量，它会正确地将所有目录中的文件添加到 ArrayList 中。但如果将其保留为局部变量，它只会添加根目录中的文件，而不会添加其他内容。有没有办法在保持 ArrayList 作为局部变量的同时使代码正常工作呢？
英文:
public static ArrayList<String> searchFiles(File currentFolder) throw NotDirectoryException {
ArrayList<String> result = new ArrayList<String>();
if(!currentFolder.isDirectory())
throw new NotDirectoryException("File is not a directory");
File[] direct = currentFolder.listFiles();
if(direct!=null) {
for (int i = 0; i< direct.length; i++){
if(direct[i].isDirectory())
searchFiles(direct[i]);
if(direct[i].isFile()&&!direct[i].isHidden())
result.add(direct[i].getName());
}
}
return result;
}
The purpose of this code is to search through all directories and sub directories and then add the eligible files into an arraylist recursively. The code works fine if I remove the ArrayList declaration from the method and put it instead as a global varible, it will correctly add all files in the directories into the arraylist. If i keep it as a local variable, it only adds the files in the root folder and nothing else. Is there a way to keep the ArrayList as a local variable while making the code work?
答案1
得分: 2
你可以将 ArrayList 传递给递归调用，如下所示：
public static ArrayList<String> searchFiles(File currentFolder, ArrayList<String> result) throws NotDirectoryException {
if (!currentFolder.isDirectory())
throw new NotDirectoryException("File is not a directory");
File[] direct = currentFolder.listFiles();
if (direct != null) {
for (int i = 0; i < direct.length; i++) {
if (direct[i].isDirectory())
searchFiles(direct[i], result);
if (direct[i].isFile() && !direct[i].isHidden())
result.add(direct[i].getName());
}
}
return result;
}
注意，当您将 `result` 声明为局部变量时，在方法返回后它将被销毁。为了保留其值，您可以在递归调用方法时将其作为参数传递。
<details>
<summary>英文:</summary>
You can pass the `ArrayList` to the recrsive call as shown below:
public static ArrayList<String> searchFiles(File currentFolder, ArrayList<String> result) throw NotDirectoryException {
if(!currentFolder.isDirectory())
throw new NotDirectoryException("File is not a directory");
File[] direct = currentFolder.listFiles();
if(direct!=null) {
for (int i = 0; i< direct.length; i++){
if(direct[i].isDirectory())
searchFiles(direct[i], result);
if(direct[i].isFile()&&!direct[i].isHidden())
result.add(direct[i].getName());
}
}
return result;
}
Note that when you declare `result` as a local variable, it will be destroyed after the method will return. In order to preserve its value, you can pass it as a parameter while calling the method recursively.
</details>
# 答案2
**得分**: 1
你所需做的就是正确地在递归中使用`searchFiles`的返回值。例如，不要再使用：
searchFiles(direct[i]);
而应该使用：
result.addAll(searchFiles(direct[i]));
在其他答案中递归地传递可变的`ArrayList`更高效，但更加令人困惑，最好配合一个没有`ArrayList`参数的方法的公共重载。此外，这将违反你问题的标题，标题指明`ArrayList`应保持为局部变量。
<details>
<summary>英文:</summary>
All you need to do is properly use the return value of `searchFiles` in the recursion. For example, instead of
searchFiles(direct[i]);
write
result.addAll(searchFiles(direct[i]));
Passing the mutable `ArrayList` recursively in other answers is more efficient, but more confusing, and is best paired with a public overload of the method without the `ArrayList` parameter. Additionally, this would violate your question's title, which specifies that the `ArrayList` should remain a local variable.
</details>
# 答案3
**得分**: 0
传入这个ArrayList。原始调用者会传入一个新的ArrayList()。
<details>
<summary>英文:</summary>
Pass in the arraylist. The original caller would pass in a new ArrayList()
</details>
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