Thank you for the reply. However, it(Oracle manual) didn't help, though.
In fact, I created another project to
test the JTextField editable property operation.
The result is "it worked very normal as I expected." And I compared the two JTextFields(problematic one and the later version of working perfect version) property by property.
Here I attached the fine version. I bet the wrong JTextField has the same value for each property. Phew,...
(Only the caret position was different. The other JTextField has '0' for it.
I appreciate your effort anyway.