java - arrayList 存储的不确定性

Question

public void openFile(){
        try {
            l = new Formatter("try.txt");
            System.out.println("Opened File");
        } catch (Exception e){
            System.out.println("Did not open file");
        }
    }
    public void addRecord(){
        l.format("%s", nameField.getText());
        System.out.println("Added Name" + " " + nameField.getText());
        }
    public void onClose(){
        l.close();
    }

/*

So I am trying to store user data, I have a gui and anytime they click sign up i want to store the namefield in an array list, is it possible that anytime I close and reopen the program and someone else puts in their name it just adds to the array list instead of overriding what the earlier person put in?
Example is in my gui i type in mike as name, I close it and reopen it and put in john as the name, would that add mike and john or would it be just john? and how do I make them co-exist?
Thank you

它会将其读取到文件中，但每次我关闭程序并再次运行它时，它都会替换第一行上的内容。

Answer 1

与 List (其中 ArrayList 是一种实现)您可以只使用 add方法。例如，如果您有一个包含单个对象(字符串“Mike”)的列表，然后执行 namesList.add("John") (其中 namesList 是 List<String> )那么列表将包含两个元素:“John”和“Mike”。

但是，您还提到了在程序执行之间保留数据。默认情况下，所有列表都纯粹内存数据存储，并且每次关闭并重新打开程序时都会被清除。为了存储它们，您需要某种形式的数据持久性。在重型方面，这将是一个完整的数据库，但对于具有简单需求的小型项目，您可以使用 SQLite - 甚至只是一个文本文件。