Instead of using JTextArea.setText(String text), use JTextArea.append(String text).
Appends the given text to the end of the document. Does nothing if the model is null or the string is null or empty.
This will add text on to the end of your JTextArea.
Another option would be to use getText() to get the text from the JTextArea, then manipulate the String (add or remove or change the String), then use setText(String text) to set the text of the JTextArea to be the new String.
When you want to create a new line or wrap in your TextArea you have to add \n (newline) after the text.
TextArea t = new TextArea();
t.setText("insert text when you want a new line add \nThen more text....);
setBounds();
setFont();
add(t);
This is the only way I was able to do it, maybe there is a simpler way but I havent discovered that yet.
Are you using JTextArea's append(String) method to add additional text?
JTextArea txtArea = new JTextArea("Hello, World\n", 20, 20);
txtArea.append("Goodbye Cruel World\n");
Source: Stackoverflow.com