指同一个人前后差别很大like two different people

• 所有人对张彦撞人后的举动都觉得很惊愕，这与她平时表现判若两人。

  Everybody was shocked at Zhang Yan's actions after she knocked into someone. It was so different from her normal self.

• 现在的琳琳和过去简直判若两人。

  The Linlin of today and the Linlin of the past are like two different people.