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Fundamentals of Java Programming Lab 11.7.2 

Copyright 

 2003, Cisco Systems, Inc. 

Lab 11.7.2  Calculator    

 
Estimated Time: 30 minutes  
 
Learning Objective:  

•  In this lab activity, the student will create a GUI using a grid layout to position 

components. 

 
Description/Scenario: 

•  This lab will create the following: 

o  A class called Calculator that has methods that will add, subtract, divide, and 

multiply.  

o  A class called CalculatorGUI that displays the calculator user interface and 

instantiates Calculator class that performs the number crunching. 

o  A class called CalculatorApp that creates a frame to display the calculator. 
o  A class called CalculatorApplet that displays the calculator in the appletviewer or 

a browser. 

 
File Management 

Open BlueJ. Click on Project from the BlueJ main menu and select New. In the New 
Project window and in the Look in: list box select c:\. Now, double click the javacourse 
folder listed in the text window and a different New Project window opens with javacourse 
in the Look in: list box. Now, double click the chap11 folder listed in the text window and a 
different New Project window opens with chap11 in the Look in: list box. Type lab11.7.2 
in the File name text box and click on Create to create a lab11.7.2 subfolder in the 
chap11 folder.  

 
Tasks: 

Step 1 Create CalculatorGUI 

a.  Create the class CalculatorGUI that uses the following design: 

 

 

b.  In the CalculatorGUI class, create buttons for 0 to 9 digits and six buttons for the 

period, equal, plus, minus, multiply, and divide. Use a 4 x 4 grid layout for the 
buttons.  

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Fundamentals of Java Programming Lab 11.7.2 

Copyright 

 2003, Cisco Systems, Inc. 

c.  Use panels and layout managers that will assist you in the CalculatorGUI design.  
d.  Add a constructor that instantiates the Calculator class and creates all attributes.  
e. Add 

a 

getContentPanel() method that returns a panel that has all necessary 

buttons and action listeners added to it.  

f.  Now, add two nested classes, OpButtonHandler & NumberButtonHandler. The 

OpButtonHandler class contains an actionPerformed() method that uses the 

Calculator class methods to compute answer to math operations. 

g.  The NumberButtonHandler class contains an actionPerformed() method that 

assigns text to the label or textfield named answer. Use the following code to create 
the CalculatorGUI class but modify the code that creates 12 separate buttons to code 
that creates an array of buttons. Use a for loop and the button array to create the 
buttons, add them to the buttonArea panel and to add the correct action listener. 

 
 Sample 

Code: 

 

private class NumberButtonHanlder implements ActionListener 
{ 
   public void actionPerformed(ActionEvent event) 
{ 
   if ( readyForNextNumber ) 
{ 
   answer.setText(event.getActionCommand()); 
   readyForNextNumber = false; 
} 
else 
} 
   answer.setText(answer.getText() + 

event.getActionCommand().charAt(0)); 
 
} 
 
}//end of if 
} 
}//end of class

 

 

 

Step 2 Create class Calculator 

a.  Create a class named Calculator that follows the UML listed below. Use the main 

method to test the math operations of the class. Use the following data for the test: 
 

Calculator calc = new Calculator(); 

System.out.println("2.0 + >> " + calc.opAdd("2.0")); 

System.out.println("3.0 = >> " + calc.opEquals("3.0")); 

   System.out.println("15.3 * >> " + calc.opMultiply("15.3")); 

   System.out.println("2.0 / >> " + calc.opDivide("2.0")); 

 
Step 3 Create class CalculatorApp 

a.  Create a class named CalculatorApp that follows the UML listed below. Have this 

class create a frame to display the CalculatorGUI class. Have the main method 
launch the frame.  

b.  Now test the operation of the calculator using the frame. 

 
Step 4 Create class CalculatorApplet 
       

a.  Create a class named CalculatorApplet that extends Applet and follows the UML 

diagram listed below. Have this class instantiate the CalculatorGUI.  

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Fundamentals of Java Programming Lab 11.7.2 

Copyright 

 2003, Cisco Systems, Inc. 

b.  Launch this applet using the appletviewer or the browser option after selecting run 

from the menu in response to the right clicking of the CalculatorApplet class in the 
BlueJ IDE.  

c.  Now test the operation of the calculator using the applet. 
d.  Which launches faster the frame or the applet?