// calc-ui-model/Calc.java -- Fred Swartz // Level : Intermediate. // Structure : Three files: main, GUI (subclass of JFrame), logic. // Components: JButton, JTextField (right justified). // Containers: JFrame, several JPanels. // Layouts : BorderLayout to put the other panels together. // Two GridLayout panels for the buttons. // Listeners : One ActionListener which is shared by all // numeric key buttons. Similarly share // an ActionListener for all operator buttons. //