single instance

single_instance.java

class User{
    static public function instance(){
        static my_user = User()
        return my_user;
    }

    public function setToken(token){
        this.token = token
    }

    public function getAvatar(){
        return this.avatar;
    }

    private token;
    private avatar;
}

class LoginActivity{
    public function login_success(token){
        user = User.instance();
        user.setToken(token);
    }
}

class MainActivity{
    public function onupdate(){
        user = User.instance();
        avatar_widget = this.avatar();
        avatar_widget.setImage(user.getAvatar());
    }
}