1.5 Itse1359-1030-variables and identifiers  (Page 7/7)

Why did this happen ?

The problem arose in the fifth line of text in Figure 8 . In this line, the programmer intended to assign a value of 16 to the existing variable named xypdq. However, because of a spelling error, the programmerinadvertently created a new variable named xyppq and assigned the new value of 16 to the new variable insteadof assigning it to the existing variable.

As a result, the value stored in the original variable named xypdq wasn't changed. When that variable was used later in an expression, the result did not meet theprogrammer's expectations.

The code visualizer

This error is illustrated in the diagram for the code visualizer in Figure 9 .

Figure 9. Visualizer showing result of a spelling error.

The code in the code window in Figure 9 is similar to the interactive code in Figure 8 .

The diagram on the right in Figure 9 shows a variable named xyppq (not xypdq) that exists solely because of a spelling error when writing the code. That variable should not exist. In addition, that variable points toan object of type int containing a value 16. That object also should not exist. (The computer does exactly what you tell it to do, even if what you tell it to do is wrong.)

Spelling errors can be dangerous

This is one of the greatest dangers of using a programming language that doesn't require the declaration of variables. This type of spelling error iseasy to make (as a result of a simple typing error) , and can be extremely difficult to find and fix.

Defending against spelling errors

The best defense against this kind of error is to make all of your variable names meaningful. Then if you make a typing error (that results in a spelling error) , you might have a better chance of finding it later.

Meaningful variable names

Some meaningful variable names follow. Note the judicious use of upper and lower case to visually break the variable name into separate recognizable words. This is anaming convention that has become very popular, particular among Java programmers. It is commonly referred to as camelCase as in thisCamelHasFourHumps .

• myUpperLimit
• yourUpperLimit
• theOverheadRate
• theFinalPrice

Remember, case is significant in variable names

The variable named MyUpperLimit is not the same variable as the one named myUpperLimit .

Miscellaneous

This section contains a variety of miscellaneous information.

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