Roll back to use the simple Class constructor to support class lock. Fix a bug for...

Roll back to use the simple Class constructor to support class lock.  Fix a bug for static field initialization: the initialization of a static field was invoked each time the field is used. The initialization of a static field should be invoked only once and be invoked before it is used. To simplify the implementation, we create a static block to contain the initializations of all the static fields of a class and invoke this static block at the beginning of the main method.