Why is char[] preferred over String for passwords?

Question

In Swing, the password field has a getPassword() (returns char[]) method instead of the usual getText() (returns String)

Answer 1

Character arrays (char[]) can be cleared after use by setting each character to zero and Strings not. If someone can somehow see the memory image, they can see a password in plain text if Strings are used, but if char[] is used, after purging data with 0's, the password is secure.