java.awt.TextField provides the ability to set an echo character.
This echo character is typically used in password entry fields to hide
the actual text typed in.

The method setEchoChar(char) is called to define the echo character.
The API does not prevent a programmer from calling setEchoChar multiple
times.
On win32 you can change the echo character as often as you like since
the win32 textfield native peer supports this.

On Solaris the Motif textfield provides no direct support for this, and an
Xt callback is installed to intercept and modify the text.

This callback is installed when the echo character is set.

On Solaris this has a bad effect since the previous callback is not
removed. We then have two callbacks each noting the characters being
typed and competing to enter their echo character.