Swing I - Java - page 948

Display 17.19 A Simple Calculator (part 2 of 4)

41 JPanel buttonPanel = new JPanel();

42 buttonPanel.setBackground(Color.GRAY);

43 buttonPanel.setLayout( new FlowLayout());

44 JButton addButton = new JButton("+");

45 addButton.addActionListener( this );

46 buttonPanel.add(addButton);

47 JButton subtractButton = new JButton(" − ");

48 subtractButton.addActionListener( this );

49 buttonPanel.add(subtractButton);

50 JButton resetButton = new JButton("Reset");

51 resetButton.addActionListener( this );

52 buttonPanel.add(resetButton);

53 add(buttonPanel, BorderLayout.CENTER);

54 }

55 public void actionPerformed(ActionEvent e)

56 {

57 try

58 {

59 assumingCorrectNumberFormats(e);

60 }

61 catch (NumberFormatException e2)

62 {

63 ioField.setText("Error: Reenter Number.");

64 }

65 }

A NumberFormatException does not need to be declared
or caught in a catch block.

66 //Throws NumberFormatException.

67 public void assumingCorrectNumberFormats(ActionEvent e)

68 {

69 String actionCommand = e.getActionCommand();

70 if (actionCommand.equals("+"))

71 {

72 result = result + stringToDouble(ioField.getText());

73 ioField.setText(Double.toString(result));

74 }

75 else if (actionCommand.equals(" − "))

76 {

77 result = result − stringToDouble(ioField.getText());

78 ioField.setText(Double.toString(result));