Java: Thread safe singleton

gistfile1.java

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

    public Object clone() throws CloneNotSupportedException {
        throw new CloneNotSupportedException();
    }

    private YourSingletonClass() {
        // construct your class
    }
    private static YourSingletonClass instance;
}