write the java code

Assume that you have created a jTextArea with the name "a1", a jTextField with the name "f1", and a jButton with the name "b1". When the button b1 is clicked, you need to take the number written in f1, if it is a multiple of 5, then append it to the end of the text area a1. If it is not, then append it to the beginning of the text area.

1. Write the code for this button handler.

2. Protect your code against any possible crashing.