Hour 24: Making Your Knowledge Add Up

NOTES AND CORRECTIONS

• One solution to your boss Ashley Judd's calculator assignment is contained in MiniCalc.java, MiniCalc.class, and CalcApplet.class (along with the two source files below). If you're working on this project and you've reached a sticking point, the following hints offer some guidance:
  • A look at the MiniCalc graphical user interface along with some information on how it was designed.
  • The full source code for the MiniCalc graphical user interface, which has been developed according to Ashley's specifications.
  • More information about the author's version of MiniCalc.

SOURCE FILES

• CalcApplet.java
• CalcApplet.html

READER QUESTIONS

• Question: In the MiniCalc solution, I am a little confused with how part of the program works. More specifically, I would like to know more about the following lines:
  • if (newText.indexOf(".") == -1)
  •     newText += ".";
• Answer: The indexOf() method of the String class searches for text inside the string -- such as a "." character in the above example. If the text is found, indexOf() returns an integer indicating the position where it was found. If it is not found, indexOf() returns -1. The above lines make sure that there isn't a "." character in newText before adding one to the string. You can find out more from Sun's official documentation for the java.lang.String class.

ACTIVITIES

• Solution #1: MiniCalc2.java, MiniCalc2.class, CalcApplet2.java, CalcApplet2.class, and CalcApplet2.html.
• Solution #2: Visit Developer.Com's Java directory. One of the categories in the Tools and Utilities section is devoted to Calculators.