Singleton class that is thread, reflection and serialization safe

Singleton.java

import java.io.Serializable;

public class Singleton implements Serializable {
    
    private static volatile Singleton sInstance;
    
    private Singleton() {
        if (sInstance != null) {
            throw new RuntimeException("Use getInstace() method to instantiate.")
        }
    }
    
    public static synchronized Singleton getInstance() {
        if (sInstance == null) {
            synchronized (Singleton.class) {
                if (sInstance == null) {
                    sInstance = new Singleton();
                }
            }
        }
        return sInstance;
    }
    
    public Singleton readResolve() {
        return getInstance();
    }
}