inputverificationdemo.java

java tutorial.sun公司官方出品。java入门书籍。最新版

                return true; //shouldn't happen
            }
        }
        
        //Checks that the amount field is valid.  If it is valid,
        //it returns true; otherwise, returns false.  If the
        //change argument is true, this method reigns in the
        //value if necessary and (even if not) sets it to the
        //parsed number so that it looks good -- no letters,
        //for example.
        
        protected boolean checkAmountField(boolean change) {
            boolean wasValid = true;
            double amount = DEFAULT_AMOUNT;
            
            //Parse the value.
            try {
                amount = moneyFormat.parse(amountField.getText()).
                        doubleValue();
            } catch (ParseException pe) {
                wasValid = false;
            }
            
            //Value was invalid.
            if ((amount < MIN_AMOUNT) || (amount > MAX_AMOUNT)) {
                wasValid = false;
                if (change) {
                    if (amount < MIN_AMOUNT) {
                        amount = MIN_AMOUNT;
                    } else { // amount is greater than MAX_AMOUNT
                        amount = MAX_AMOUNT;
                    }
                }
            }
            
            //Whether value was valid or not, format it nicely.
            if (change) {
                amountField.setText(moneyFormat.format(amount));
                amountField.selectAll();
            }
            
            return wasValid;
        }
        
        //Checks that the rate field is valid.  If it is valid,
        //it returns true; otherwise, returns false.  If the
        //change argument is true, this method reigns in the
        //value if necessary and (even if not) sets it to the
        //parsed number so that it looks good -- no letters,
        //for example.
        protected boolean checkRateField(boolean change) {
            boolean wasValid = true;
            double rate = DEFAULT_RATE;
            
            //Parse the value.
            try {
                rate = percentFormat.parse(rateField.getText()).
                        doubleValue();
            } catch (ParseException pe) {
                wasValid = false;
                pe.printStackTrace();
            }
            
            //Value was invalid.
            if (rate < MIN_RATE) {
                wasValid = false;
                if (change) {
                    rate = MIN_RATE;
                }
            }
            
            //Whether value was valid or not, format it nicely.
            if (change) {
                rateField.setText(percentFormat.format(rate));
                rateField.selectAll();
            }
            
            return wasValid;
        }
        
        //Checks that the numPeriods field is valid.  If it is valid,
        //it returns true; otherwise, returns false.  If the
        //change argument is true, this method reigns in the
        //value if necessary and (even if not) sets it to the
        //parsed number so that it looks good -- no letters,
        //for example.
        protected boolean checkNumPeriodsField(boolean change) {
            boolean wasValid = true;
            int numPeriods = DEFAULT_PERIOD;
            
            //Parse the value.
            try {
                numPeriods = decimalFormat.parse(numPeriodsField.getText()).
                        intValue();
            } catch (ParseException pe) {
                wasValid = false;
                pe.printStackTrace();
            }
            
            //Value was invalid.
            if ((numPeriods < MIN_PERIOD) || (numPeriods > MAX_PERIOD)) {
                wasValid = false;
                if (change) {
                    if (numPeriods < MIN_PERIOD) {
                        numPeriods = MIN_PERIOD;
                    } else { // numPeriods is greater than MAX_PERIOD
                        numPeriods = MAX_PERIOD;
                    }
                }
            }
            
            //Whether value was valid or not, format it nicely.
            if (change) {
                numPeriodsField.setText(decimalFormat.format(numPeriods));
                numPeriodsField.selectAll();
            }
            
            return wasValid;
        }
        
        public void actionPerformed(ActionEvent e) {
            JTextField source = (JTextField)e.getSource();
            shouldYieldFocus(source); //ignore return value
            source.selectAll();
        }
    }
    
    public static void main(String[] args) {
        
        /* Use an appropriate Look and Feel */
        try {
            //UIManager.setLookAndFeel("com.sun.java.swing.plaf.windows.WindowsLookAndFeel");
            //UIManager.setLookAndFeel("com.sun.java.swing.plaf.gtk.GTKLookAndFeel");
            UIManager.setLookAndFeel("javax.swing.plaf.metal.MetalLookAndFeel");
        } catch (UnsupportedLookAndFeelException ex) {
            ex.printStackTrace();
        } catch (IllegalAccessException ex) {
            ex.printStackTrace();
        } catch (InstantiationException ex) {
            ex.printStackTrace();
        } catch (ClassNotFoundException ex) {
            ex.printStackTrace();
        }
        /* Turn off metal's use of bold fonts */
        UIManager.put("swing.boldMetal", Boolean.FALSE);
        
        //Schedule a job for the event-dispatching thread:
        //creating and showing this application's GUI.
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI();
            }
        });
    }
    
    /**
     * Create the GUI and show it.  For thread safety,
     * this method should be invoked from the
     * event-dispatching thread.
     */
    private static void createAndShowGUI() {
        //Create and set up the window.
        JFrame frame = new JFrame("InputVerificationDemo");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        
        //Create and set up the content pane.
        JComponent newContentPane = new InputVerificationDemo();
        newContentPane.setOpaque(true); //content panes must be opaque
        frame.setContentPane(newContentPane);
        
        //Display the window.
        frame.pack();
        frame.setVisible(true);
    }
    
    //Compute the monthly payment based on the loan amount,
    //APR, and length of loan.
    double computePayment(double loanAmt, double rate, int numPeriods) {
        double I, partial1, denominator, answer;
        
        numPeriods *= 12;        //get number of months
        if (rate > 0.01) {
            I = rate / 100.0 / 12.0;         //get monthly rate from annual
            partial1 = Math.pow((1 + I), (0.0 - numPeriods));
            denominator = (1 - partial1) / I;
        } else { //rate ~= 0
            denominator = numPeriods;
        }
        
        answer = (-1 * loanAmt) / denominator;
        return answer;
    }
    
    //Create and set up number formats. These objects are used
    //for both parsing input and formatting output.
    private void setUpFormats() {
        moneyFormat = (NumberFormat)NumberFormat.getNumberInstance();
        
        percentFormat = NumberFormat.getNumberInstance();
        percentFormat.setMinimumFractionDigits(3);
        
        decimalFormat = (DecimalFormat)NumberFormat.getNumberInstance();
        decimalFormat.setParseIntegerOnly(true);
        
        paymentFormat = (DecimalFormat)NumberFormat.getNumberInstance();
        paymentFormat.setMaximumFractionDigits(2);
        paymentFormat.setNegativePrefix("(");
        paymentFormat.setNegativeSuffix(")");
    }
}