Singleton - Posts - OneCompiler

public class Singleton {
private static volatile Singleton instance;

private Singleton() {

    if (instance != null) {
        throw new RuntimeException("Use getInstance() method to get the single instance");
    }
}

public static Singleton getInstance() {
    if (instance == null) {
        synchronized (Singleton.class) {
            if (instance == null) {
                instance = new Singleton();
            }
        }
    }
    return instance;
}

public void showMessage() {
    System.out.println("Hello from Singleton! Instance hash: " + this.hashCode());
}
}