Swing I - Absolute Java - page 1003

Display 17.19 A Simple Calculator (part 2 of 4)

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));
79 }
80 else if (actionCommand.equals("Reset"))
81 {
82 result = 0.0;
83 ioField.setText("0.0");
84 }
85 else
86 ioField.setText("Unexpected error.");
87 }

(continued)