Hibernate findByID implementation

I found the 开发者_如何学JAVAfollowing code on net for fetching a object from DB.Now what does lock indicates?? Whe does it lock?

public T findById(ID id, boolean lock) {
        T entity;
        if (lock) {
            entity = (T) getSession().load(getPersistentClass(), id, LockMode.UPGRADE);
        } else {
            entity = (T) getSession().load(getPersistentClass(), id);
        }

        return entity;
    }

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It just uses the appropriate Hibernate LockMode. If you have a more specific question, it might be easier to answer.