Create Singleton

Singleton is a design pattern that keeps the instance one and only one forever.

With dependency injection, you won't need to create a static instance for singleton:

public class TesterSingleton {

    private final Map<String, String> collection = new HashMap<>();

    public void setKey(String key, String value){
        this.collection.put(key, value);
    }

    public String getString(){
        return this.collection.toString();
    }
}

then register it in main class

   @Override
    public void bindServices(ServiceCollection serviceCollection) {
        serviceCollection.addSingleton(TesterSingleton.class);
    }

then you can use it with injectable instances

(spigot for example)

public class TesterLifeCycle implements ELDLifeCycle {

    @Inject
    private TesterSingleton singleton;

    @Inject
    private TestConfig config;

    @Override
    public void onEnable(JavaPlugin javaPlugin) {
        singleton.setKey("abc", "xya");
        singleton.setKey("xyz", "abc");
        javaPlugin.getLogger().info(singleton.getString());
        javaPlugin.getLogger().info(config.toString());
    }

    @Override
    public void onDisable(JavaPlugin javaPlugin) {
        javaPlugin.getLogger().info(singleton.getString());
        javaPlugin.getLogger().info(config.toString());
    }
}