首页 \ 问答 \ 如何在TreeSet或TreeMap中添加ArrayList元素(How to add ArrayList elements in TreeSet or TreeMap)

如何在TreeSet或TreeMap中添加ArrayList元素(How to add ArrayList elements in TreeSet or TreeMap)

 众所周知，我们需要实现Comparable接口，并在使用TreeSet时添加compareTo（）。 不这样做会抛出ClassCastException。 现在我有一个TreeSet，我需要添加ArrayLists作为TreeSet的元素。  
 如果我们写：  
ArrayList al = new ArrayList();
ArrayList al2 = new ArrayList();
ArrayList al3 = new ArrayList();
TreeSet ts = new TreeSet();
ts.add(al);
ts.add(al2);
ts.add(al3);
 
 它抛出ClassCastException。  
 问题 ：如何将ArrayList istances（不是它们的元素）添加到TreeSet或TreeMap？ 

As we all know, we need to implement Comparable interface and add compareTo() when we work with TreeSet. Not doing so will throw ClassCastException. Now I have a TreeSet and I need to add ArrayLists as elements of TreeSet. 
if we write: 
ArrayList al = new ArrayList();
ArrayList al2 = new ArrayList();
ArrayList al3 = new ArrayList();
TreeSet ts = new TreeSet();
ts.add(al);
ts.add(al2);
ts.add(al3);
 
It throws ClassCastException. 
Question: How can I add ArrayList istances (not their elements) to a TreeSet or TreeMap?

原文：https://stackoverflow.com/questions/35613475

更新时间：2023-03-31 09:03

最满意答案

 我会从另一个答案重复一遍：  
 
  从API级别8（Android 2.2）开始，如果将应用程序构建为可调试的，可以使用shell run-as命令将命令或可执行文件作为特定用户/应用程序运行，或者切换到应用程序的UID ，以便您可以访问其数据目录。  
 
 因此，如果您希望从设备中拉出应用程序数据库，则应运行应用程序的调试版本，连接到adb shell并运行以下命令：  
run-as com.yourpackage sh -c "cat ~/databases/db-file" > /sdcard/db-file.sqlite
 
 这将将您的db-file复制到SD卡/外部存储的根目录。 现在，您可以使用文件管理器， adb pull或其他任何您喜欢的方式轻松获取。 请注意，通过这种方法，您的应用程序不需要具有WRITE_EXTERNAL_STORAGE权限，因为复制由可以永久写入外部存储的shell用户完成。  
 在Linux / Mac系统上，可以使用以下命令将数据库直接复制到您的计算机，而无需输入adb shell：  
adb shell 'run-as com.yourpackage sh -c "cat ~/databases/db-file"' > db-file.sqlite
 
 然而，由于CR / LF符号转换，Windows将无法正常工作。 在那里使用以前的方法。 

I'll repeat myself from another answer: 
 
 Starting from API level 8 (Android 2.2), if you build the application as debuggable, you can use the shell run-as command to run a command or executable as a specific user/application or just switch to the UID of your application so you can access its data directory. 
 
So if you wish to pull your application database from the device you should run the debug build of the application, connect with adb shell and run the following command: 
run-as com.yourpackage sh -c "cat ~/databases/db-file" > /sdcard/db-file.sqlite
 
This will copy your db-file to the root of your SD card / external storage. Now you can easily get it from there by using file manager, adb pull or whatever else you like. Note that with this approach, there is NO need for your app to have WRITE_EXTERNAL_STORAGE permission, as the copying is done by the shell user who can always write to the external storage. 
On Linux/Mac systems there is a possibility to copy a database directly to your computer with the following command one can use without entering the adb shell: 
adb shell 'run-as com.yourpackage sh -c "cat ~/databases/db-file"' > db-file.sqlite
 
This however will not work correctly on Windows because of CR/LF symbols conversion. Use the former method there.

如何在TreeSet或TreeMap中添加ArrayList元素(How to add ArrayList elements in TreeSet or TreeMap)

最满意答案

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