Extract Variable
Problem
You have an expression that is hard to understand.
Solution
Place the result of the expression or its parts in separate variables that are self-explanatory.
Before
void renderBanner() {
if ((platform.toUpperCase().indexOf("MAC") > -1) &&
(browser.toUpperCase().indexOf("IE") > -1) &&
wasInitialized() && resize > 0 )
{
// do something
}
}
After
void renderBanner() {
final boolean isMacOs = platform.toUpperCase().indexOf("MAC") > -1;
final boolean isIE = browser.toUpperCase().indexOf("IE") > -1;
final boolean wasResized = resize > 0;
if (isMacOs && isIE && wasInitialized() && wasResized) {
// do something
}
}
Why Refactor
The main reason for extracting variables is to make a complex expression more understandable, by dividing it into its intermediate parts.
These could be:
- Condition of the
if()
operator or a part of the?:
operator in C-based languages - A long arithmetic expression without intermediate results
- Long multipart lines
Extracting a variable may be the first step towards performing Extract Method if you see that the extracted expression is used in other places in your code.
Benefits
- More readable code! Try to give the extracted variables good names that announce the variable’s purpose loud and clear. More readability, fewer long-winded comments. Go for names like
customerTaxValue
,cityUnemploymentRate
,clientSalutationString
, etc.
Drawbacks
- More variables are present in your code. But this is counterbalanced by the ease of reading your code.
How to Refactor
-
Insert a new line before the relevant expression and declare a new variable there. Assign part of the complex expression to this variable.
-
Replace that part of the expression with the new variable.
-
Repeat the process for all complex parts of the expression.