Just use a TableModel implementation (often a (anonymous) DefaultTableModel subclass) that overrides getColumnClass to return Integer.class for columns 3 and 5. JTable has built-in support for numbers, so there will be validation upon input.
I need to popup an alert message for the user to key-in numeric values.
This system is a questionnaire targeting for the public to give their feedback.
So, it will be more informed if the system prompt an alert message rather than the red line.
please help how can i make an alert instead the red bolder?
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