Owl Sams Teach Yourself Java 2 in 24 Hours

Hour 24: Making Your Knowledge Add Up


  • One solution to the calculator assignment is contained in MiniCalc.java, MiniCalc.class, CalcApplet.java, CalcApplet.class and CalcApplet.html.
  • This project uses a MiniCalc component that can be added to applets or applications as needed. The CalcApplet files contain a simple applet that's used to display MiniCalc as part of the applet's interface. This is handled by making MiniCalc a subclass of JPanel, the most basic Swing container.
  • The MiniCalc class contains three instance variables, which are defined in the following statements:
    • char operator = 0;
    • float storedValue = 0;
    • boolean clearNext = false;

    The operator variable is used to keep track of the current mathematical operation: addition, subtraction, multiplication, or division. It does this by storing the text of the key that was pressed: '+', '-', '*', or '/'. The storedvalue variable is used to keep track of the first number involved in an operation (if you pressed the '5', '+', and '7' keys, storedvalue would equal 5 when the equals key was pressed. The clearNext variable is used to indicate when the display should be cleared after the next key is pressed. This is needed after every operation so that a new calculation can be performed.

  • No other variables are needed for the class itself. The class stores the current calculation and the final result in the text field at the top of the interface.
  • If you have questions about this solution, contact the author. I hope you'll publish the source code to your own solution for this project, so I can offer a link to it on this site. I look forward to seeing what readers are able to create.


  • None