Rule Definition
While disabling debug logging level in production, it still impacts performance of your application because the method invocation involves the hidden cost of parameter construction. For example: << cat.debug("Entry number: " + i + " is " + String.valueOf(entry[i])) >> incurs the cost of constructing the message parameter that is converting both integer i and entry[i] to a String and concatenating intermediate strings, regardless of whether the message will be logged or not.

Remediation
Add a if condition with a call to isDebugEnabled() before calling any .debug().

Violation Code Sample

import org.apache.log4j.*;

public class MyClass {
    Category cat = Category.getInstance(MyClass.class.getName());
    String entry [];

    public static void aMethod(int i) {

        cat.debug("Entry number: " + i + " is " + String.valueOf(entry[i])); // VIOLATION
   }

Fixed Code Sample

import org.apache.log4j.*;

public class MyClass {
    Category cat = Category.getInstance(MyClass.class.getName());
    String entry [];

    public static void aMethod(int i) {

        if (cat.isDebugEnabled()) { //FIXED
            cat.debug("Entry number: " + i + " is " + String.valueOf(entry[i])); 
        }
   }

http://www.javaworld.com/jw-11-2000/jw-1122-log4j.html http://burtbeckwith.com/blog/?cat=8