java - 如何防止在内部存储中存储重复的字符串

Question

我尝试了两天但没有成功。我在 fragment 的 onStop 方法中将 arraylist 保存在内部存储中，然后在 onresume 方法中从内部存储中获取此数据。我正在检查字符串是否存在于内部存储的数组列表中，以防止在内部存储中存储重复的字符串，但这似乎不起作用。它每次都会在内部存储中存储重复的字符串。我不明白我在这里做错了什么。我将非常感谢您的帮助。

 public void saveTitleList (){
    try {
        FileOutputStream fileOutputStream= mContext.openFileOutput("radiotitle2.txt",MODE_PRIVATE);
        DataOutputStream dataOutputStream=new DataOutputStream(fileOutputStream);
        dataOutputStream.writeInt(stationName2.size());
        ArrayList<String> titletest=getTitleList();
        for(String line:stationName2){
            if(!titletest.contains(line)){//here i am checking for duplicate strings in intenal file
                dataOutputStream.writeUTF(line);
                Log.d("title2 saved",line);
            }

        }
        dataOutputStream.flush();
        dataOutputStream.close();
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
}
public ArrayList<String> getTitleList(){
    ArrayList<String> titleList= new ArrayList<>();
    try {
        FileInputStream fileInputStream= mContext.openFileInput("radiotitle2.txt");
        DataInputStream dataInputStream= new DataInputStream(fileInputStream);
        int size=dataInputStream.readInt();
        for(int i =0;i<size;i++){
            String line=dataInputStream.readUTF();
            titleList.add(line);
            Log.d("title2 from storage",line);
        }
        dataInputStream.close();
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
    return titleList;
}

Answer 1

ArrayList 允许重复，而 HashSet 不允许重复。您应该使用 HashSet .

The important feature of Set interface is it does not allow the elements in duplicates; stores unique elements.

 HashSet <String> titleList= new HashSet <String>();

    try {
    FileInputStream fileInputStream= mContext.openFileInput("radiotitle2.txt");
    DataInputStream dataInputStream= new DataInputStream(fileInputStream);
    int size=dataInputStream.readInt();
    for(int i =0;i<size;i++){
        String line=dataInputStream.readUTF();
        titleList.add(line);
        Log.d("title2 from storage",line);
    }
   ......