4. Write a program called UserLoginApp, user interface as shown below,

- the size is 250*180,

- username and password is stored within the file user.txt, with contents (format: username password):

Zhangsan 123456

Lisi 654321

Wangwu 123123

- OK button clicked to check the username and password, if the username is not in the list, display username not exited!; if the password is not correct, display password not correct!,

- Cancel button clicked to remove user input, and set prompt info back to Plz enter username and password.,

- Exit button clicked to exit the program.

0 O Login Username: Password: OK Cancel Exit Plz enter username and password