Notes on Session J4: Boolean Expressions and Conditionals

Experiment J4.6, Step 4. It is likely that you failed in your attempt. Java only lets you switch on selected primitive types, and not on strings and other objects.

Experiment J4.7, Step 5. Hopefully, you've observed that the capitalization used within the param tag does not affect the passing of the parameter to the applet. In fact, the Java specification says that parameters are case-insensitive.

Experiment J4.7, Step 6. Hopefully, you've observed that the capitalization of the string used with getParameter tag does not affect the passing of the parameter to the applet. In both cases (param tag and getParameter), the Java specification says that parameters are case-insensitive.

Experiment J4.7, Step 7. It may seem confusing that the parameter is called greeting in the HTML file, but is stored in the variable message within the applet. However, Java does not require you to use the same name for the variable that stores a parameter that you've used for naming the parameter. We'll take advantage of this ability to choose a different internal name in the next experiment.

Experiment J4.7, Step 8. As you may have surmised, there is no longer a parameter tag for the greeting parameter that the applet expects. Hence, the call getParameter("greeting") returns null. The drawString method is unhappy with the null string and gives an error.

Experiment J4.8, Step 1. Since the applet does not yet read these new parameters, they have no effect.

Experiment J4.8, Step 4. While the name of the parameter is case-insensitive, the value of the parameter is case-sensitive. Java treats "white" and "WHITE" as different strings. Hence, none of the strings match the applet never changes fontColor from Color.red (which it was set to at the start of the paint method).

Experiment J4.8, Step 10. As suggested earlier, the try/catch permits us to specify a default value. More imporantly, it stops the program from reporting an error when we use values that Java does not know how to convert.