Java Static class 用于保存中间变量

Question

I create a middle class save many variables in it, example:

public static class Middle{
    public static List<Student> listStudent = new ArrayList<>();
    public static String level = 1; (this example of level of a character in the game)
}

And assign value for those variables

class A{
    Middle.listStudent = GetData();
    Middle.level++;
    
    Intent intent = new Intent(A.this, B.class);
    startActivity(intent)
}

And then in next class (or activity) we using those variables with new data

class B{
    ShowResult(Middle.listStudent);
    ShowResult(Middle.level);
}

I using this way because don't want to transfer data by Intent.

My question is, can we using this way too much in the whole application without getting any issue, and if the middle class it shut down for any reason, makes losing data?

Answer 1

1. If some static class become shutdown, maybe some serious error occurs in your application.The JVM had to exit.

2. In multithreading environment,this way can cause dirty read and brings into some strange thing.

You can try the code below. And see what's going on.

public static void main(String[] args) {

    // create three threads to run it
    for (int i = 0; i < 3; i++) {

        //simulate multi-threaded environment
        new Thread(() -> {
            for (int j = 0; j < 10; j++) {
                StaticData.listStudent.add(Thread.currentThread().getName() + ":" + j);
                StaticData.level++;
            }
        }).start();
    }

    //show the last result , in single thread ,result must be 30 31 ,but maybe not this in multi-threaded environment
    System.out.println("Total Result listStudent's size is :" + StaticData.listStudent.size());
    System.out.println("Total Result level is :" + StaticData.level);

}

public static class StaticData {
    public static List<String> listStudent = new ArrayList<>();
    public static Integer level = 1;
}