Singleton instantiation

Below show is the creation on the singleton object.

public class Map_en_US extends mapTree {

    private static Map_en_US m_instance;

    private Map_en_US() {}

    static{
        m_instance = new Map_en_US();
        m_instance.init();
    }

    public static Map_en_US getInstance(){
        return m_instance;
    }

    @Override
    protected void init() {
        //some code;
    }
}

My question is what is the reason for using a static block for instantiating. i am familiar with below form of instantiation of the singleton.

public static Map_en_US getInstance(){
    if(m_instance==null)
      m_instance = new Map_en_US();
}