The GUI form should have three text fields on the form for data entry. One of the fields should be numeric.
Please find attached a solution (547243.java) that demonstrates the features you wanted in your program. Java version 1.7.0_21 was used during development ...
Data read from the file is appended after the existing entries in the table. Solution also suggests what changes to make in the code, in case you want to start with an empty table each time you read data from the file.