Your constructor should look something like:
public NotePad() {
setTitle("NOTEPAD");
setSize(700, 500);
setDefaultCloseOperation(EXIT_ON_CLOSE);
setLayout(new FlowLayout());
txtArea = new JTextArea();
mnuBar = new JMenuBar();
mnyFile = new JMenu("File");
mnyFormat = new JMenu("Format");
mnyEdit = new JMenu("Edit");
mnyHelp = new JMenu("Help");
openFile = new JMenuItem("Open");
saveFile = new JMenuItem("Save");
exit = new JMenuItem("Exit");
textWrap = new JMenuItem("Text Wrap");
noTextWrap = new JMenuItem("No Text Wrap");
clear = new JMenuItem("Clear");
abtNotepad = new JMenuItem("About Notepad");
mnuBar.add(mnyFile);
mnuBar.add(mnyFormat);
mnuBar.add(mnyEdit);
mnuBar.add(mnyHelp);
mnyFile.add(openFile);
mnyFile.add(saveFile);
mnyFile.add(exit);
mnyFormat.add(textWrap);
mnyFormat.add(noTextWrap);
mnyEdit.add(clear);
mnyHelp.add(abtNotepad);
setJMenuBar(mnuBar);
add(txtArea);
setVisible(true);
}
Otherwise you are overriding each component you add to BorderLayout.