Unused variable
Why is this an issue?
A local variable that is declared and then never read is dead code. It makes the method harder to follow, and it is often the leftover of a half-finished edit where a value was meant to be used and never was.
If the declaration has an initializer, that work still runs at execution time, including a SOQL query whose result is thrown away.
Examples
Example of incorrect code:
public Integer compute() {
Integer a = 1; // never read
Integer b = 2;
return b;
}
Example of correct code:
public Integer compute() {
Integer b = 2;
return b;
}
How can I fix violations?
Delete the declaration. If the initializer has a side effect you need to keep, such as a DML statement or a method call that changes state, keep the call and drop the assignment.
Configuration options
You can configure whether variables whose name starts with an underscore (for example _unused) are allowed. This is enabled by default.
When should I disable this rule?
Only declarations inside a method body, a constructor body or a trigger body are considered, so fields, constants, catch variables and managed package classes are never reported.
Dismiss individual issues where a variable is consumed somewhere the analyzer cannot see. The most common case is a dynamic SOQL bind (:variableName) whose query text is assembled in another class.
Resources