CodeQL documentation

Unread local variable

ID: java/local-variable-is-never-read
Kind: problem
Severity: recommendation
Precision: high
Tags:
   - maintainability
   - useless-code
   - external/cwe/cwe-561
Query suites:
   - java-security-and-quality.qls

Click to see the query in the CodeQL repository

A local variable that is never read is useless.

As a matter of good practice, there should be no unused or useless code. It makes the program more difficult to understand and maintain, and can waste a programmer’s time.

Recommendation

This rule applies to variables that are never used as well as variables that are only written to but never read. In both cases, ensure that no operations are missing that would use the local variable. If appropriate, simply remove the declaration. However, if the variable is written to, ensure that any side-effects in the assignments are retained. (For further details, see the example.)

Example

In the following example, the local variable oldQuantity is assigned a value but never read. In the fixed version of the example, the variable is removed but the call to items.put in the assignment is retained.

// Version containing unread local variable
public class Cart {
	private Map<Item, Integer> items = ...;
	public void add(Item i) {
		Integer quantity = items.get(i);
		if (quantity = null)
			quantity = 1;
		else
			quantity++;
		Integer oldQuantity = items.put(i, quantity);  // AVOID: Unread local variable
	}
}

// Version with unread local variable removed
public class Cart {
	private Map<Item, Integer> items = ...;
	public void add(Item i) {
		Integer quantity = items.get(i);
		if (quantity = null)
			quantity = 1;
		else
			quantity++;
		items.put(i, quantity);
	}
}

References