(Tip Calculator Modification) The Tip Calculator app from Section 25.5 does not

ID: 3777261 • Letter: #

Question

(Tip Calculator Modification) The Tip Calculator app from Section 25.5 does not need a Button to perform its calculations. Reimplement this app to use property listeners to perform the calculations whenever the user modifies the bill amount or changes the custom tip percentage. Also use a property binding to update the Label that displays the tip percentage.

// TipCalculator.java
// Main application class that loads and displays the Tip Calculator's GUI.
import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.stage.Stage;

public class TipCalculator extends Application
{
@Override
public void start(Stage stage) throws Exception
{
Parent root =
FXMLLoader.load(getClass().getResource("TipCalculator.fxml"));

Scene scene = new Scene(root); // attach scene graph to scene
stage.setTitle("Tip Calculator"); // displayed in window's title bar
stage.setScene(scene); // attach scene to stage
stage.show(); // display the stage
}

public static void main(String[] args)
{
// create a TipCalculator object and call its start method
launch(args);
}
}

/**************************************************************************
* (C) Copyright 1992-2014 by Deitel & Associates, Inc. and *
* Pearson Education, Inc. All Rights Reserved. *
* *
* DISCLAIMER: The authors and publisher of this book have used their *
* best efforts in preparing the book. These efforts include the *
* development, research, and testing of the theories and programs *
* to determine their effectiveness. The authors and publisher make *
* no warranty of any kind, expressed or implied, with regard to these *
* programs or to the documentation contained in these books. The authors *
* and publisher shall not be liable in any event for incidental or *
* consequential damages in connection with, or arising out of, the *
* furnishing, performance, or use of these programs. *
*************************************************************************/

// TipCalculatorController.java
// Controller that handles calculateButton and tipPercentageSlider events
import java.math.BigDecimal;
import java.math.RoundingMode;
import java.text.NumberFormat;
import javafx.beans.value.ChangeListener;
import javafx.beans.value.ObservableValue;
import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.scene.control.Label;
import javafx.scene.control.Slider;
import javafx.scene.control.TextField;

public class TipCalculatorController
{
// formatters for currency and percentages
private static final NumberFormat currency =
NumberFormat.getCurrencyInstance();
private static final NumberFormat percent =
NumberFormat.getPercentInstance();

private BigDecimal tipPercentage = new BigDecimal(0.15); // 15% default

// GUI controls defined in FXML and used by the controller's code
@FXML
private TextField amountTextField;

@FXML
private Label tipPercentageLabel;

@FXML
private Slider tipPercentageSlider;

@FXML
private TextField tipTextField;

@FXML
private TextField totalTextField;

// calculates and displays the tip and total amounts
@FXML
private void calculateButtonPressed(ActionEvent event)
{
try
{
BigDecimal amount = new BigDecimal(amountTextField.getText());
BigDecimal tip = amount.multiply(tipPercentage);
BigDecimal total = amount.add(tip);

tipTextField.setText(currency.format(tip));
totalTextField.setText(currency.format(total));
}
catch (NumberFormatException ex)
{
amountTextField.setText("Enter amount");
amountTextField.selectAll();
amountTextField.requestFocus();
}
}

// called by FXMLLoader to initialize the controller
public void initialize()
{
// 0-4 rounds down, 5-9 rounds up
currency.setRoundingMode(RoundingMode.HALF_UP);

// listener for changes to tipPercentageSlider's value
tipPercentageSlider.valueProperty().addListener(
new ChangeListener()
{
@Override
public void changed(ObservableValue ov,
Number oldValue, Number newValue)
{
tipPercentage =
BigDecimal.valueOf(newValue.intValue() / 100.0);
tipPercentageLabel.setText(percent.format(tipPercentage));
}
}
);
}
}

Explanation / Answer

package com.deitel.tipcalculator;

import android.os.Bundle; // for saving state information

import android.support.v7.app.AppCompatActivity; // base class

import android.text.Editable; // for EditText event handling

import android.text.TextWatcher; // EditText listener

import android.widget.EditText; // for bill amount input

import android.widget.SeekBar; // for changing the tip percentage

import android.widget.SeekBar.OnSeekBarChangeListener; // SeekBar listener

import android.widget.TextView; // for displaying text

import java.text.NumberFormat; // for currency formatting

public class MainActivity extends Activity {

private static final NumberFormat currencyFormat =

NumberFormat.getCurrencyInstance();

private static final NumberFormat percentFormat =

NumberFormat.getPercentInstance();

private double billAmount = 0.0; // bill amount entered by the user

private double percent = 0.15; // initial tip percentage

private TextView amountTextView; // shows formatted bill amount

private TextView percentTextView; // shows tip percentage

private TextView tipTextView; // shows calculated tip amount

private TextView totalTextView; // shows calculated total bill amount

// called when the activity is first created

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState); // call superclass's version

setContentView(R.layout.activity_main); // inflate the GUI

// get references to programmatically manipulated TextViews

amountTextView = (TextView) findViewById(R.id.amountTextView);

percentTextView = (TextView) findViewById(R.id.percentTextView);

tipTextView = (TextView) findViewById(R.id.tipTextView);

totalTextView = (TextView) findViewById(R.id.totalTextView);

tipTextView.setText(currencyFormat.format(0)); // set text to 0

totalTextView.setText(currencyFormat.format(0)); // set text to 0

// set amountEditText's TextWatcher

EditText amountEditText =

(EditText) findViewById(R.id.amountEditText);

amountEditText.addTextChangedListener(amountEditTextWatcher);

// set percentSeekBar's OnSeekBarChangeListener

SeekBar percentSeekBar =

(SeekBar) findViewById(R.id.percentSeekBar);

percentSeekBar.setOnSeekBarChangeListener(seekBarListener);

}

// calculate and display tip and total amounts

private void calculate() {

// format percent and display in percentTextView

percentTextView.setText(percentFormat.format(percent));

// calculate the tip and total

double tip = billAmount * percent;

double total = billAmount + tip;

// display tip and total formatted as currency

tipTextView.setText(currencyFormat.format(tip));

totalTextView.setText(currencyFormat.format(total));

}

// listener object for the SeekBar's progress changed events

private final OnSeekBarChangeListener seekBarListener =

new OnSeekBarChangeListener() {

// update percent, then call calculate

@Override

public void onProgressChanged(SeekBar seekBar, int progress,

boolean fromUser) {

percent = progress / 100.0;// set percent based on progress

calculate(); // calculate and display tip and total

}

@Override

public void onStartTrackingTouch(SeekBar seekBar) { }

@Override

public void onStopTrackingTouch(SeekBar seekBar) { }

};

// listener object for the EditText's text-changed events

private final TextWatcher amountEditTextWatcher = new TextWatcher() {

// called when the user modifies the bill amount

@Override

public void onTextChanged(CharSequence s, int start,

int before, int count) {

try { // get bill amount and display currency formatted value

billAmount = Double.parseDouble(s.toString()) / 100.0;

amountTextView.setText(currencyFormat.format(billAmount));

}

catch (NumberFormatException e) { // if s is empty or non-numeric

amountTextView.setText("");

billAmount = 0.0;

}

calculate(); // update the tip and total TextViews

}

@Override

public void afterTextChanged(Editable s) { }

@Override

public void beforeTextChanged(

CharSequence s, int start, int count, int after) { }

};

}

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(Tip Calculator Modification) The Tip Calculator app from Section 25.5 does not

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