How to save variable value of the last session(program exit)

Question

How can i save the value of a variable in my program and then reuse it at the next program run ? I don't want to do it with file write/read.

Answer 1

Use the Java Preferences API.

import java.util.prefs.*;

public class Example {
    // Preference key
    private static final String FRUIT = "fruit";

    public void savePreference(String favoriteFruit) {
        Preferences prefs = Preferences.userNodeForPackage(Example.class);

        prefs.put(FRUIT, favoriteFruit);
    }

    public String readPreference() {
        Preferences prefs = Preferences.userNodeForPackage(Example.class);

        return prefs.get(FRUIT, "default");
    }
}

The data is stored based on the fully-qualified name of your class, so your package name and class name are relevant. From the documentation for the Preferences class:

This class allows applications to store and retrieve user and system preference and configuration data. This data is stored persistently in an implementation-dependent backing store. Typical implementations include flat files, OS-specific registries, directory servers and SQL databases. The user of this class needn't be concerned with details of the backing store.

Answer 2

One can store settings using java.util.prefs.Preferences. For two target groups: normally user settings, and less often application/system settings. They can use the platform settings, like under Windows.

There exists however also the possibility to store the settings as XML, which is a cleaner way, as it does not touch the Windows registry, which might be protected. Then a customary location would be inside a directory like ".myapp" under the directory System.getProperty("user.home").

Answer 3

You can use an in-memory key-value store like Redis, or an in-memory database like H2. But this may be overkill depending on your needs.