为一个对象的类设置变量，并从该类的另一个对象访问相同的值

Question

Here are the three classes.

1. input.java
2. Middle.java
3. Output.java

In this scenario, Middle.java has a static global variable x.

I'm setting the value of x from the input.java class using setter method. and now I want to access the same value of x from the output.java using getter method. But when I try to do this, it doesn't do that. Here are the class files.

1. Input.java

     public class Input { public static void main(String[] args) { Middle m = new Middle(); m.setX(100); } } 

2.Middle.java

    public class Middle {
public static int x;

public void setX(int value)
{
    x = value;
}

public int getX()
{
    return x;
}
}   

3. Ouput.java

    public class Output {

public static void main(String[] args) {        
    Middle m = new Middle();
    int temp = m.getX();
    System.out.print(temp);
}
}

So, when I run the input.java program first and set the value to 100 and then run the output.java program, the output I must get is 100. but I don't get that.

Answer 1

As you know, values held in objects will become inaccessible after your program stops running. Therefore, you need to store the value somewhere permanently so it can be read the next time you run the program.

One way to do this is to write the value to a file on your hard drive:

try (FileWriter writer = new FileWriter("/some/path/to/a/file.txt")) {
    writer.write(yourValue);
} catch (IOException e) {
    e.printStackTrace();
}

And then you can read it like this:

try (FileReader reader = new FileReader("/Users/mulangsu/Desktop/temp.txt")) {
    System.out.println(reader.read());
} catch (FileNotFoundException e) {
    System.out.println("File not found");
} catch (IOException e) {
    e.printStackTrace();
}

Another way to do this is to save your values to a web server. This way, your value can persist over different devices.