Package com.puppycrawl.tools.checkstyle.checks.coding

Class UnusedLocalVariableCheck

  • All Implemented Interfaces:
    Configurable, Contextualizable
    public class UnusedLocalVariableCheck
extends AbstractCheck

    Checks that a local variable is declared and/or assigned, but not used. Doesn't support pattern variables yet. Doesn't check array components as array components are classified as different kind of variables by JLS.

    To configure the check: 

     <module name="UnusedLocalVariable"/>

    Example: 

     class Test {

     int a;

     {
         int k = 12; // violation, assigned and updated but never used
         k++;
     }

     Test(int a) {   // ok as 'a' is a constructor parameter not a local variable
         this.a = 12;
     }

     void method(int b) {
         int a = 10;             // violation
         int[] arr = {1, 2, 3};  // violation
         int[] anotherArr = {1}; // ok
         anotherArr[0] = 4;
     }

     String convertValue(String newValue) {
         String s = newValue.toLowerCase(); // violation
         return newValue.toLowerCase();
     }

     void read() throws IOException {
         BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
         String s; // violation
         while ((s = reader.readLine()) != null) {
         }
         try (BufferedReader reader1 // ok as 'reader1' is a resource and resources are closed
                                     // at the end of the statement
             = new BufferedReader(new FileReader("abc.txt"))) {
         }
         try {
         } catch (Exception e) {     // ok as e is an exception parameter
         }
     }

     void loops() {
         int j = 12;
         for (int i = 0; j < 11; i++) { // violation, unused local variable 'i'.
         }
         for (int p = 0; j < 11; p++)   // ok
             p /= 2;
     }

     void lambdas() {
         Predicate<String> obj = (String str) -> { // ok as 'str' is a lambda parameter
             return true;
         };
         obj.test("test");
     }
 }

    Parent is com.puppycrawl.tools.checkstyle.TreeWalker

    Violation Message Keys:

    • unused.local.var
    Since:
    9.3